Many records of Eupanthalis kinbergi in the Mediterranean actually belong to Euarche tubifex Ehlers, 1887, including the description by Fauvel (1923) (Pettibone 1989). Arvanitidis (2000a) reports both Euarche tubifex and Eupanthalis kinbergi in his checklist of Aegean polychaetes, re-assigning all records of Eupanthalis kinbergi that were probably identified using the key by Fauvel (1923) to Euarche tubifex, but no primary records of Euarche tubifex from Greece exist.

Questionable status. In the Mediterranean only reported from Greece (Bogdanos and Satsmadjis 1983, Bogdanos and Satsmadjis 1987, NCMR 1989). Commonly distributed in the Greater Caribbean Region.

Type locality: Mediterranean.

Type locality: Mediterranean (Croatia).

Originally described from the Hellenic Trench (Matapan Deep; 35°49'48''N, 22°20'42''E; 4690 m depth), no other records from Greece.

Reported from Greece by Simboura and Zenetos (2005). Type locality: Mediterranean (Banyuls-sur-Mer, France).

Questionable status. In the Mediterranean, only reported from Greece (Kisseleva 1961). Record doubted by Arvanitidis (1994) and Çınar et al. (2014) based on the species' ecology: Alkmaria romijni is typically a brackish water species but has been reported from a depth of 65–100 m in the open waters of the Aegean Sea.

Type locality: Mediterranean (Adriatic).

Questionable status. Mediterranean records of Ampharete acutifrons in the Mediterranean are doubted by several authors (e.g. Parapar et al. 1993a, Mikac 2015) based on the species' boreal distribution. Specimens of Ampharete acutifrons from the Adriatic were shown to belong to Ampharete lindstroemi Hessle, 1917 (Mikac 2015), thus Ampharete acutifrons may actually be absent from the region. Jirkov (2001) considers Ampharete acutifrons to probably constitute a species complex, based on observed differences between Atlantic and Pacific species.

Ampharete grubei had long been considered a junior synonym of Ampharete acutifrons (Grube, 1860) and was reinstated by Jirkov (2001). Primary literature records from Greece under the name Ampharete grubei exist but were subsequently reported by Arvanitidis (2000a) and Simboura and Nicolaidou (2001) as Ampharete acutifrons.

Reported from worldwide locations but probably restricted to circumpolar areas; specimens from other regions may belong to other species (Jirkov 2008).

Questionable status. Few records from the Mediterranean outside Greece (e.g. Spain: Nebra et al. 2011; France: Guérin and Massé 1976) otherwise known from the European Atlantic coasts. Arvanitidis (1994) regards its presence in the Mediterranean as doubtful.

Originally described from the Hellenic Trench (Matapan Deep; 36°01'48''N, 22°24'36''E; 3174 m depth), no other records from Greece. Considered endemic to the type locality (Paterson et al. 2009).

Reported from Greece by Arvanitidis (1994). In the Mediterranean also reported from the western basin (Fauvel and Rullier 1959), otherwise distributed in the Caribbean and tropical Atlantic. Chloeia viridis is the name prevailing in literature, with Chloeia candida as a synonym (referred to synonymy by Hartman (1948), although Barroso and Paiva (2011) stress that this synonymy should be re-evaluated). The publication year of Kinberg's species is sometimes cited as 1910, but the species was in fact described in 1857 (Kinberg 1857) and thus the name Chloeia candida takes priority.

Type locality: Mediterranean (Sicily).

Böggemann (2009) examined the syntypes of Chloenopsis atlantica and postulated a possible synonymy of Chloenopsis atlantica with Bathychloeia sibogae Horst, 1910. However, Kudenov and Borda (2013), having studied the types of the monotypic genera Chloenopsis and Bathychloeia, consider both genera distinct.

Species complex. Reported from Greece by Chatzigeorgiou et al. (2016) based on a single specimen (identified using Day (1967) and Barroso et al. (2010)). Eurythoe complanata is a complex of cryptic and pseudo-cryptic species (Barroso et al. 2010, Arias et al. 2013a), containing two cryptic forms of Eurythoe complanata and the species Eurythoe laevisetis Fauvel, 1914, which differs from Eurythoe complanata sensu stricto by the absence of harpoon-shaped notochaetae (Arias et al. 2013a). In the Mediterranean, two of the species in this species complex occur: Eurythoe laevisetis in the central and western basin, and Eurythoe complanata in the eastern basin and the Alboran Sea. Both species are native to the Caribbean and tropical Atlantic and non-native to the Mediterranean, but their exact pathways of introduction to the Mediterranean and thus the identity of the species occurring in the eastern basin are yet unknown (Arias et al. 2013a).

The identity of the circumtropical species Hermodice carunculata has been the subject of several investigations during the last years. Yáñez-Rivera and Salazar-Vallejo (2011), based on morphological investigations of fixed and living specimens, resurrected Hermodice nigrolineata Baird, 1868 for the Eastern Atlantic and Mediterranean populations of the species. Ahrens et al. (2013) found no genetic differences between Hermodice carunculata populations of the Caribbean and the Eastern Atlantic and Mediterranean and placed Hermodice nigrolineata again into synonymy with Hermodice carunculata. The findings of Chatzigeorgiou et al. (2014) concerning the phylogenetic relationships of the eastern Mediterranean populations of Hermodice carunculata support the results of Ahrens et al. (2013).

Reported from Greece by Chatzigeorgiou et al. (2016). Atlantic species, considered alien to the Mediterranean (Çınar 2009). Known from Turkey and Cyprus (Çınar 2009), Italy (Cosentino and Giacobbe 2010) and Egypt (Dorgham et al. 2014).

Questionable status. The Greek records of Notopygos megalops probably belong to a different species. Notopygos megalops was originally described based on a juvenile specimen from the Caribbean Sea and used to be considered a synonym of Notopygos crinita (Grube, 1855) before it was re-described by Yáñez-Rivera and Carrera-Parra (2012) from the Caribbean Sea based on adult characters. This re-description of Notopygos megalops differs from the description by Fauvel (1923) (which was probably used for the identification of the Greek specimens) in the following characters: Branchiae from chaetiger 6 (Yáñez-Rivera and Carrera-Parra 2012) instead of chaetiger 7 (Fauvel 1923); anterior branchiae with main stem and seven branchial filaments, in median chaetigers branching into four stems with five to seven filaments each (Yáñez-Rivera and Carrera-Parra 2012) vs. small tufts of 2–4 filaments anteriorly and only a single papilliform filament anteriorly Fauvel (1923). Yáñez-Rivera and Carrera-Parra (2012) define the start of the branchiae on chaetiger 6 as characteristic for the species; this seems to be invariable in juvenile individuals, too (McIntosh 1895). Thus, the species described by Fauvel (1923) and any specimens identified based on his description probably belong to a different species.

Questionable status. Reported from Greece by Kisseleva (1983). Distributed in the boreal Atlantic, in the Mediterranean reported from the western basin (e.g. Jacquotte 1963, Bellan 1964a). The species' presence in Greece is doubtful, as it has not been reported from the Mediterranean for over three decades and is usually distributed in colder waters.

Specimens of Aphrodita aculeata from the Adriatic and Aegean may have been confused with Aphrodita alta Kinberg, 1865 or Aphrodita perarmata Roule, 1898 (Barnich and Fiege 2000b). In addition, the description of Aphrodita aculeata by Fauvel (1923) contains elements of both Aphrodita aculeata and Aphrodita alta, thus specimens identified using Fauvel's key may belong to either species.

Questionable status. Reported from Greece by Marinov (1959), otherwise only known from the type locality in the North-East Atlantic. Aphrodita perarmata, Aphrodita aculeata Linnaeus, 1758 and Aphrodita alta Kinberg, 1865 are easily confused and all records require verification (Barnich and Fiege 2000b).

Reported from Greece by Arvanitidis (2000a) based on a single specimen; in the Mediterranean also known from France (Bellan 1964a), Spain (Campoy 1982), Cyprus (Çınar 2005), Italy (Castelli et al. 2008) and the Adriatic (Mikac 2015), otherwise distributed in the North Atlantic.

Type locality: Mediterranean.

Type locality: Mediterranean.

Type locality: Mediterranean.

Questionable status. Reported from Greece by Antoniadou et al. (2006) from rocky shores. The record is considered questionable on the basis of habitat and geographic distribution (the species occurs in tidal mudflats of the European Atlantic coast and North Sea).

Reported from Greece by Arvanitidis (1994) and Chatzigeorgiou et al. (2016). In the Mediterranean also known from Israel (Ben-Eliahu 1976b), Tunisia (Cantone et al. 1978), Spain (Alós 1990), Italy (Castelli et al. 2008), Egypt (Abd-Elnaby 2009), Turkey (Çınar et al. 2014) and the Adriatic (Mikac 2015), otherwise distributed in the East Atlantic (Gravina 1991).

Originally described from Greece as parasitic on the starfish species Sclerasterias richardi (Perrier in Milne-Edwards 1882) and Sclerasterias neglecta (Perrier, 1891) collected near Santorini, Kythira and Samos; no other records from Greece. Almost nothing is known of the species' distribution; the extensive description of its anatomy by Stummer-Traunfels (1903) is based on specimens provided by Marenzeller, presumably from the same collection as the type material.

Questionable status. Species complex. Several sibling species have been separated from Capitella capitata sensu lato worldwide since Grassle and Grassle (1976) showed it to constitute a complex of species. Blake (2009) restricts Capitella capitata sensu stricto to Arctic areas and considers Mediterranean specimens, including the description by Fauvel (1927), to show significant differences to Capitella capitata and thus to belong to other species. In Greece, there is evidence so far of at least another sibling species population (Gamenick et al. 1998). However, because of the high morphological similarity of the various sibling species, they cannot be reliably distinguished in routine investigations (Blake 2000). See also notes under Capitella teleta Blake, Grassle & Eckelbarger, 2009.

Reported from Greece by Maidanou et al. (2017). Capitella teleta is one of the sibling species which used to be referred to as Capitella sp. I in laboratory and genetic studies (Blake et al. 2009). In the Mediterranean also known from France (Blake et al. 2009) and Turkey (Çınar et al. 2017). Present in the adjacent Sea of Marmara (Çinar et al. 2015) and Black Sea (Kurt-Şahin et al. 2017). Otherwise distributed in the North Atlantic and Pacific Ocean.

Questionable status. Listed by Arvanitidis (2000a), subsequently included in the checklist by Simboura and Nicolaidou (2001) but in fact based on a record from the Turkish Aegean, which is considered questionable by Çınar et al. (2014). The actual first record of the species from Greece is by Akoumianaki (2004). However, this species can be confused with several species of Notomastus Sars, 1851, based only on the thoracic chaetal formula which was traditionally used for identification. Green (2002) clarified some inaccuracies in previous descriptions of Capitellethus and used the teeth pattern in hooks as a reliable differentiating character between these two genera. If the presence of this species in Greece can be confirmed, it should be regarded as a non-native species. Originally described from New Zealand.

Type locality: Mediterranean.

Type locality: Mediterranean (Gulf of Naples).

Questionable status. In the Mediterranean only reported from Greece (Akoumianaki 2004). Distributed in the Eastern Pacific, the Greater Caribbean and questionably in the Red Sea (Wehe and Fiege 2002).

Frequently reported from Greece and other parts of the Mediterranean; type locality: Mediterranean (Port-Vendres, France). Green (2002) clarified confusions that had arisen from typographic errors in the genus designation made by Hutchings and Rainer (1981). However, a number of problems concerning the correct identification of the species still exist. Juvenile specimens can be confused with adults of Mediomastus species, since chaetigers four and five initially carry hooks which are replaced by capillaries with age (Capaccioni-Azzati and El-Haddad 2015). In addition, different opinions regarding the presence and location of abdominal gills exist in literature (Capaccioni-Azzati and El-Haddad 2015).

Bellan (1964a) proposed the synonymy of Leiocapitella glabra (type locality California) with Leiocapitella dollfusi (originally described from the Moroccan coasts) based on the overlapping variability in the chaetal formula of the two species. Ben-Eliahu and Fiege (1995), probably unaware of Bellan (1964a), proposed a possible synonymy of Leiocapitella dollfusi with Leiocapitella glabra on the basis of the identical hook dentition, in addition to the chaetal formula (Capaccioni-Azzati and El-Haddad 2015). However, it is noteworthy that the presence of branchiae in posterior segments, a character reported by Fauvel (1936a) for Leiocapitella dollfusi, has not been confirmed in material previously identified as Leiocapitella glabra (Hartman 1947, Ben-Eliahu and Fiege 1995), due to lack of posterior parts. In the present study, in agreement with Bellan (1964a), and Capaccioni-Azzati and El-Haddad (2015), we consider the older name Leiocapitella dollfusi as having priority over Leiocapitella glabra.

Reported from Greece by Akoumianaki (2004) and Neofitou et al. (2014). In the Mediterranean also known from Egypt (Abd-Elnaby 2009). Originally described from the Red Sea.

Questionable status. In the Mediterranean only reported from Greece (Akoumianaki 2004). Commonly distributed in the Pacific. Worldwide, records of this genus are rare and uncertain (e.g. Hilbig and Blake 2006, Probert et al. 2009). However, as species of Leiochrides can key out as Leiochrus in Fauchald (1977), the presence of the former genus in Greece is possible if the key by Fauchald has been used.

Type locality: Mediterranean (Gulf of Naples).

Reported from Greece by Maidanou et al. (2017). Originally from South Africa, in the Mediterranean also known from Italy (Castelli et al. 2008), Cyprus (Çınar 2005), Spain (Capaccioni-Azzati and El-Haddad 2015) and the Adriatic (Mikac 2015). Zenetos et al. (2005) and Zenetos et al. (2010) question the identification of the species in the Mediterranean, but without providing specific information.

Questionable status. In the Mediterranean only reported from Greece (Akoumianaki 2004). Commonly distributed in the East Pacific.

In the Mediterranean only reported from Greece, by Dando et al. (1995) from shallow hydrothermal vents and by Simboura and Zenetos (2005) from a depth of 1250 m. Commonly distributed in deep sea habitats of the East Pacific, the Chukchi Sea and possibly the Bay of Biscay (Simboura and Zenetos 2005), thus the record by Dando et al. (1995) is considered questionable as it is from a shallow-water habitat.

Questionable status. Reported from Greece by NCMR (1992), Simboura (1996) and Katsiaras and Simboura (2015). In the Mediterranean also known from Italy (Gravina and Somaschini 1990), Spain (Capaccioni-Azzati et al. 1992), Cyprus (Çınar 2005), Turkey (Çınar et al. 2014) and the Adriatic (Mikac 2015). Originally described from Brazil. However, Capaccioni-Azzati and El-Haddad (2015) list some noteworthy inconsistencies amongst Mediterranean records and the original description regarding the presence of chaetae on the peristomium and the last setiger with capillaries present. Therefore, it is likely that the Mediterranean records belong to an undescribed species.

Natively distributed in East Africa and the Red Sea, first Mediterranean record from Greece (Harmelin 1968), nowadays distributed throughout the Mediterranean (Capaccioni-Azzati and El-Haddad 2015).

Type locality: Mediterranean (Gulf of Naples).

Morphologically very similar to Notomastus profundus (Eisig, 1887), therefore some authors have suggested a possible synonymy between the two species (Capaccioni-Azzati and El-Haddad 2015; references within).

Reported from Greece by Koukouras (1979) and Papazacharias (1991). Type locality: Mediterranean (Gulf of Naples).

Type locality: Mediterranean (Gulf of Naples).

Originally described from specimens collected in Marseilles and the Greek islands of Crete and Santorini.

Type locality: Mediterranean (French Riviera).

Type locality: Mediterranean (Gulf of Lion).

Type locality: Mediterranean.

Type locality: Mediterranean (Gulf of Naples).

Reported from Greece by Pérès (1959). Type locality: Mediterranean (Adriatic).

Type locality: Mediterranean (Gulf of Naples).

Species complex. Spiochaetopterus costarum was long believed to be a cosmopolitan species but in fact the name has been applied to a number of pseudo-cryptic species (e.g. Bhaud 1998, Bhaud et al. 2003). Mediterranean specimens are currently considered to belong to Spiochaetopterus costarum sensu stricto, as the type locality of the species is in the Gulf of Naples.

Reported from Greece by Makra and Nicolaidou (2000) and Tselepides (1992). In the Mediterranean also reported from France (Guille and Laubier 1966) and the Adriatic (Mikac 2015). Bhaud (1998) restricts the species' distribution to the boreal Atlantic and considers it absent from the temperate waters of the Mediterranean, but the report by Tselepides is from deep waters (500 m and 700 m) off Crete, where environmental conditions could be more favourable for the species. Other boreal species have been shown to occur in deep Mediterranean waters (Fiege et al. 2000a).

Type locality: Mediterranean (Adriatic).

Type locality: Mediterranean (Villfranche-sur-Mer, France).

Recently identified from Greece (Watson and Chatzigeorgiou, submitted) based on two specimens from Crete (for details see Record 1; Record 2).

In the Mediterranean only reported from Greece (Simboura 1996, as Aphelochaeta cf. monilaris). Commonly distributed along the Pacific coast of North America. The Greek material differs from Hartman's original description mainly in the number of thoracic chaetigers (11 vs. 15 in the species described by Hartman 1960) and in the absence of eyespots (two eyespots in Hartman's material) and may belong to a different taxon (Simboura 1996).

Type locality: Mediterranean.

Mediterranean records could also comprise specimens of the recently described Caulleriella mediterranea Lezzi, 2017 which differs from Caulleriella alata mainly in having a biannulate instead of triannulate prostomium (Lezzi 2017).

Reported from Greece by Maidanou et al. (2017). The only other Mediterranean record is an unconfirmed record from Corsica (Ifremer 2016) and neither of the two Mediterranean reports is accompanied by a taxonomic description. Originally described from Madeira, little is known on its distribution range. If its presence is confirmed, the species should probably be considered non-native to the Mediterranean.

Reported from Greece by Simboura et al. (2010), found several times afterwards (HCMR, unpublished data). In the Mediterranean also known from Turkey (Çınar et al. 2014) and the Adriatic Sea (Munari et al. 2017). Chambers et al. (2011) doubt the validity of the Mediterranean records and the presence of the species in the Mediterranean (mainly on the basis of its Pacific distribution) but Le Garrec et al. (2016) present evidence of a wide distribution of the species in the Bay of Biscay, indicating that Chaetozone corona is an established alien species along the coasts of Europe and was probably introduced via shipping from its native distribution.

Reported from Greece by Simboura et al. (2010) and Katsiaras and Simboura (2015). In the Mediterranean also known from Tunisia (Zaâbi et al. 2012), Turkey (Çınar et al. 2014) and the Adriatic (Mikac 2015); otherwise distributed around the British Isles and along the European Atlantic coasts. Chambers et al. (2011) remark that records of Chaetozone gibber from the Mediterranean could in fact belong to other species, as the Mediterranean environment differs significantly from conditions in the species' native distribution range.

Questionable status. Species complex. Chaetozone setosa is a complex of pseudo-cryptic species, with at least five species in northern Europe alone (Chambers and Woodham 2003). Several authors (e.g. Simboura 1996, Çınar and Ergen 2007, Mikac 2015) doubt the validity of Mediterranean records, as the species has likely been confused with Chaetozone gibber Woodham & Chambers, 1994, Chaetozone corona Berkeley & Berkeley, 1941 or Chaetozone carpenteri McIntosh, 1911 and probably does not occur in the Mediterranean.

Chambers et al. (2011) remark that records of Chaetozone zetlandica might be misidentifications, as the Mediterranean environment differs significantly from conditions in the species' native distribution range in the North Atlantic.

Species complex. Often considered cosmopolitan, but ecological, morphological and genetic differences have been found in specimens from different geographical locations (Petersen 1999, Carr et al. 2011, Weidhase et al. 2014).

In the Mediterranean only reported from Greece (e.g. Bogdanos and Satsmadjis 1983, Bogdanos and Satsmadjis 1987, Simboura 1996; full reference list in Suppl. material 2). Known from South Africa. Identification of several Greek specimens confirmed by P. H. Gibson (pers. comm. in Simboura 1996).

Questionable status. Castelli et al. (2008) and Mikac (2015) consider the presence of the species in the Mediterranean uncertain as it may have been confused with Dodecaceria saxicola (Grube, 1855), Dodecaceria sextentaculata (Delle Chiaje, 1822), Dodecaceria fimbriata (Verrill, 1880) or Dodecaceria joubini Gravier, 1905. Several Greek specimens were examined by P.H. Gibson and differ from the northern European species; instead, different species (e.g. Dodecaceria joubini) could be present in Greece (P.H. Gibson, pers. comm. in Simboura 1996). The identification of Dodecaceria species depends on reproductive characteristics (Gibson 1978) but it is unknown which form was described by Ørsted. Thus, identity of Dodecaceria concharum is confused and Ørsted's original species is probably not valid due to an insufficient original description and loss of type material (Gibson 2015). Neotypes were designated by Gibson and Heppell (1995), but it is unclear whether these correspond to the original species of Ørsted.

Reported from Greece by Chatzigeorgiou et al. (2016). Type locality: Mediterranean (Villefranche-sur-Mer, France). As the species had long been treated as a synonym of Dodecaceria concharum Ørsted, 1843 it may be underreported.

A species reported from worldwide locations, partly caused by inaccurate descriptions in the past; therefore Blake (2016) considers the presence of Kirkegaardia dorsobranchialis in the Mediterranean uncertain and possibly restricted to West and South Africa. Many Greek records of Kirkegaardia dorsobranchialis belong in fact to Kirkegaardia heterochaeta (Laubier, 1961), as Blake (1991) had synonymised Monticellina heterochaeta with Monticellina dorsobranchialis. The distinction between the two species is difficult. Kirkegaardia heterochaeta has a longer peristomium than Kirkegaardia dorsobranchialis and posesses a mid-dorsal ridge within the dorsal channel which is absent in Kirkegaardia dorsobranchialis. The most reliable factor for their separation is the methyl green staining pattern (Blake 2016).

Possibly underreported, as the species was considered a synonym of Kirkegaardia dorsobranchialis (Kirkegaard, 1959) by Blake (1991) and reported under the latter name until Blake (1996) revoked the synonymy. Type locality: Mediterranean (France).

Questionable status. Reported from Greece by Koulouri et al. (2015). In the Mediterranean also reported from Spain (Desbruyères et al. 1973) and Turkey (Çınar et al. 2014). Çınar (2005) reports morphological differences in chaetal features between specimens from Cyprus and the original description of Kirkegaardia tesselata, concluding that the material might belong to an undescribed species. Blake (2016), having examined a specimen of Kirkegaardia from France, refers this specimen and the literature references of Monticellina tesselata by Çınar et al. (2014) and Çınar (2005) to an undescribed Kirkegaardia species (Kirkegaardia sp. A). He restricts the distribution of Kirkegaardia tesselata to California. Greek specimens possibly do not belong to Kirkegaardia tesselata but the material would require re-examination to confirm its identity.

Questionable status; species complex. Reported from Greece by NCMR (1989). Reported from worldwide locations but the species constitutes a complex of pseudo-cryptic species (Petersen 1991). Originally described from the Gulf of Naples and the only known species of the genus in the Mediterranean until the recent description of Protocirroneris purgamentorum Lezzi, Çınar & Giangrande, 2016. While it is possible that the species occurs in Greece, it has so far only been reported in grey literature and has not been found in almost three decades, therefore its presence in Greece is here considered questionable.

Species complex. Timarete filigera has been recorded from worldwide locations, but many of these records probably belong to different species. Specimens from West Atlantic localities identified as Timarete filigera were re-examined morphologically and genetically by Magalhães et al. (2014) and shown to belong to undescribed species or to species previously treated as synonyms of Timarete filigera. Mediterranean specimens are currently considered to belong to Timarete filigera sensu stricto, as the type locality of the species is in the Gulf of Naples.

Species complex. Timarete punctata, originally described from the Caribbean, constitutes a complex of cryptic species. Molecular analyses of specimens morphologically identified as Timarete punctata by Seixas et al. (2017) revealed that samples from the West Atlantic and the Pacific comprise two cryptic species, one of them widely distributed and exhibiting a low genetic diversity, the other restricted to a single location. The authors hypothesise that the low genetic diversity of the widely distributed cryptic species could be attributed to a recent human-mediated introduction at these sites. In the Mediterranean reported from Greece (Maidanou et al. 2017) and Turkey (Çınar et al. 2014).

Questionable status. Arvanitidis (1994) questions the presence of the species in the area, as the description of the specimen found by Bogdanos and Fredj (1983) shows differences both to the species described by Kitamori (1960) and to Cossura soyeri Laubier, 1964. Without re-examination of the Mediterranean specimens referred to Cossura coasta, the status of the species in the area remains doubtful.

Type locality: Mediterranean (Banyuls-sur-Mer, France)

Reported from Greece by Makra and Nicolaidou (2000), also found by Papageorgiou et al. (2006) (unpublished dataset). Type locality: Mediterranean.

Type locality: Mediterranean (Adriatic). Considered cosmopolitan. However, Jumars (1974) notes differences between populations and suggests the possibility of more than one species existing under the name of Dorvillea rubrovittata.

Reported from Greece by Corsini-Foka et al. (2015). In the Mediterranean also known from Turkey (Çınar 2009), natively distributed in the Indo-Pacific Ocean and Red Sea.

Species complex. Reported from Greece by Åkesson (1984). Neotype from the Gulf of Naples. At least 15 sibling species have been reported under the Ophryotrocha labronica group worldwide (Åkesson and Paxton 2005), four of which have been recently described from areas including the Mediterranean by Paxton and Åkesson (2010): Ophryotrocha japonica, Ophryotrocha macrovifera, Ophryotrocha robusta and Ophryotrocha rubra.

Species complex. Neotype from Genoa, Italy. Simboura and Nicolaidou (2001) report Ophryotrocha puerilis from Greece at species level, as it is reported on other parts of the Mediterranean as well (Castelli et al. 2008, Çınar et al. 2014, Núñez et al. 2013, Mikac 2015). However, Taboada et al. (2017) provide molecular evidence of at least two cryptic species under the name Ophryotrocha puerilis in the Mediterranean Sea.

Reported from Greece by Eleftheriou et al. (1990) and Dando et al. (1995). In the Mediterranean also known from Italy (Gambi et al. 1998) and Turkey (Çınar et al. 2014); otherwise distributed in the North Atlantic and the North-East Pacific.

Type locality: Mediterranean (Águilas, Spain).

Questionable status. Reported from Greece by Vamvakopoulou (1991). In the Mediterranean also known from Tunisia (Zaâbi et al. 2009) and the Adriatic (Mikac 2015). Originally described from deep waters off the Azores (Atlantic); as the Greek record is from a lagoonal habitat, it must be considered questionable.

In the Mediterranean reported from Greece (Bogdanos and Satsmadjis 1983, Bogdanos and Diapoulis 1984, Simboura et al. 1995b) and Egypt (Abd-Elnaby and Gab-Alla 2007), otherwise distributed in the Indo-Pacific, South Africa and Brazil.

Type locality: Mediterranean (Gulf of Naples).

One specimen from Greece in the collections of the Senckenberg Museum (SMF 15256, 35°52'58.2"N, 27°42'49.2"E, 115 m depth, coll. date 2005-09-05, det. D. Fiege). Type locality: Mediterranean (Adriatic).

Questionable status. Reported from Greece by Simboura (1987) and Zenetos et al. (1997). Type locality: Mediterranean (Adriatic). The original description by Pettibone (1986) is based on juveniles and needs to be completed with adult characters; Grubeulepis katzmanni may turn out to be a juvenile of Grubeulepis augeneri Pettibone, 1969 (Pettibone 1986).

Questionable status. Fauvel (1923) recorded Eunice roussaei Quatrefages, 1866 in the Adriatic Sea, but the species was later synonymised with Eunice aphroditois by Hartman (1944). Subsequently, several records of large-sized eunicids in the Mediterranean were assigned to the latter. After the resurrection of Eunice roussaei by Fauchald (1992), many authors suggested that literature records of Eunice aphroditois in the Mediterranean actually belong to Eunice roussaei (Parapar and Harto 2001, Zanol and Bettoso 2006, Çınar et al. 2014, Mikac 2015). Two specimens of Eunice aphroditois from the collections of the Aristotle University of Thessaloniki were re-examined by the first author and identified as Eunice roussaei (Faulwetter et al. 2013); it is likely that all Greek records belong to Eunice roussaei.

Questionable status. Reported from Greece by Kisseleva (1983). In the Mediterranean also known from the western basin (e.g. Bellan 1959, Fredj 1974), Cyprus (Argyrou et al. 1999) and the Adriatic (Casellato and Stefanon 2008). Otherwise distributed in the Greater Caribbean (Fauchald et al. 2009). Commonly occurs in coralligenous habitats (Casellato and Stefanon 2008), which are little studied in Greece. However, no clear description based on Mediterranean material exists. Fauvel (1923), considers Leodice gunneri (Storm, 1880) a synonym of Eunice floridana. Day (1967) lists Eunice floridana sensu Fauvel (1923) as a synonym of Eunice norvegica (Linnaeus, 1767) and Fauchald (1992) considers Leodice gunneri a synonym of the latter. Clear differentiating characters between Eunice floridana and Eunice norvegica can be found in Fauchald (1992) and Carrera-Parra and Salazar-Vallejo (1998) (which were, however, not published at the time the species was recorded from Greece).

Questionable status. Reported from Greece by NCMR (1989). In the Mediterranean also known from the western basin (e.g. Danovaro et al. 2010, Taviani et al. 2015), Tunisia (Ayari et al. 2009), the Italian coasts of the Ionian Sea (e.g. Tursi et al. 2004, Vertino et al. 2010) and the Adriatic (D'Onghia et al. 2015), otherwise distributed in the North Atlantic. Often associated with deep-water corals (Danovaro et al. 2010), which are little studied in Greece. The species has so far only been reported in grey literature and has not been found in almost three decades, therefore its presence in Greece is pending confirmation. See also notes under Eunice floridana on the confusion regarding the species concept in early works and keys.

Reported from Greece by Arvanitidis (1994) and Kitsos (2003). Type locality: Mediterranean (Adriatic). Arvanitidis (1994) notes some differences in the individuals he examined compared to the description provided by Fauchald (1992). Fauvel (1917) regards Eunice purpurea as junior synonym of Eunice roussaei Quatrefages, 1866 and the species has since then been part of the confusion concerning large eunicids in the Mediterranean (see remarks under Eunice aphroditois Pallas, 1788). Fauchald (1992) considers it a valid species by investigating material from the Adriatic and Zanol and Bettoso (2006) highlight specific differences that do not occur in Eunice roussaei.

Reported from Greece by Kisseleva (1983). Probably underreported, as records of Eunice aphroditois (Pallas, 1788) from Greece likely belong to Eunice roussaei (see notes under Eunice aphroditois).

Questionable status. Reported from Greece by NCMR (1992). Type locality: Mediterranean (Gulf of Naples). Commonly occurs in coralligenous habitats (Casellato and Stefanon 2008), which are little studied in Greece. While it is possible that the species occurs in Greece, it has so far only been reported in grey literature and has not been found in over two decades, therefore its presence in Greece is here considered questionable.

Type locality: Mediterranean (Gulf of Naples).

Records of Leodice harassii could include specimens of Eunice rubrocincta Ehlers, 1868, a Mediterranean species which Fauvel (1923) considered synonymous with Leodice harassii. Leodice rubrocincta was resurrected by Fauchald (1992) and is included as a valid species in the key by Carrera-Parra and Salazar-Vallejo (1998).

The species resembles Leodice laurillardi (Quatrefages, 1866) in a number of diagnostic characters. The latter was synonymised with Leodice torquata by Pruvot and Racovitza (1895); this was accepted by Fauvel (1923) and later authors. However, Fauchald (1992) resurrected Leodice laurillardi as a valid species and Arias et al. (2015) re-described the species based on type material and new specimens from the Mediterranean. They suggest that Leodice laurillardi could be much more widespread than previously thought but was possibly being overlooked in the Mediterranean due to the confusion with Leodice torquata.

Questionable status. Frequently reported from Greece and other parts of the Mediterranean (Martín 1987, Sardá 1991, Giangrande et al. 2003, Mikac 2015). However, Çınar (2005) and Kurt Şahin and Çınar (2009) suggest that the species closely resembles the native species Lysidice margaritacea Claparède, 1868 and question the presence of Lysidice collaris in the Eastern Mediterranean. Type locality in the Red Sea, but reported from circumtropical locations.

Species complex. Frequently reported from Greece. However, Iannotta et al. (2006) and Iannotta et al. (2009) investigated molecular markers and provided evidence of sibling species within the Lysidice ninetta complex. Two morphotypes (dark and light), differentiated by colour patterns in anterior body and acicular chaetae, were identified. Although the dark type matches well the original description, it is still unresolved whether one or both morphotypes are new species or belong to previously described species.

The genus Nematonereis Schmarda, 1860 was synonymised with Lysidice Lamarck, 1818 by Zanol et al. (2013). Type locality: Mediterranean (Adriatic).

In the Mediterranean only reported from Greece (Katsiaras et al. 2014) from Posidonia oceanica meadows, a little studied habitat in Greece. Distributed in the Indo-Pacific. The authors note that data are currently insufficient to draw conclusions on the species' native or alien distribution.

Several Greek specimens reported by Simboura et al. (2010) as Marphysa disjuncta Hartman, 1961 were re-examined by Kurt Şahin (2014) and assigned to Marphysa cinari. Type locality: Sea of Marmara.

Type locality: Mediterranean (Marseille).

Species complex. Considered cosmopolitan in the past, but Marphysa sanguinea actually comprises a complex of numerous pseudo-cryptic species (Zanol et al. 2016). Hutchings and Karageorgopoulos (2003) designated a neotype based on pectinate chaetae distribution instead of branchiae and Hutchings et al. (2012) encourage re-examination of all material outside the English Channel and North Sea. Recent studies have described several new species similar to Marphysa sanguinea or resurrected species from synonymy with the latter (Lewis and Karageorgopoulos 2008, Molina-Acevedo and Carrera-Parra 2015, Zanol et al. 2016, Liu et al. 2017). Wijnhoven and Dekker (2010) question the presence of Marphysa sanguinea in the Mediterranean Sea and encourage comparisons of specimens with the neotype.

Type locality: Mediterranean (Palermo, Sicily, Italy).

Questionable status. Reported from Greece by Bogdanos and Satsmadjis (1983). In the Mediterranean also reported from the Levantine Basin (Ben-Eliahu 1995) and questionably from the Adriatic (Mikac 2015), otherwise distributed in the Indo-Pacific. It might either be an overlooked alien species in the area or a misidentification.

Questionable status. In the Mediterranean only reported from Greece (Kisseleva 1961, Diapoulis and Bogdanos 1983). Both Greek records are from a fully marine environment and therefore considered questionable by Arvanitidis (1994), as the species usually occurs in brackish waters. However, Harris (1970) reports the species from non-brackish environments in the British Isles and assumes that it can tolerate full salinity at least during certain stages of its life cycle. Based on the geographic range of Manayunkia aestuarina, the Greek records must nevertheless be considered uncertain. Undescribed species of Manayunkia exist in Greece (Chintiroglou et al. 2004) and the genus needs further study in the region.

New record for Greece. Eleven specimens, Lesvos Island, 38°59'54''N, 26°32'26''E, 6 m depth, Posidonia oceanica meadow, collected in the framework of the PhD of N. Katsiaras. Literature used for identification: Licciano and Giangrande (2006). Type locality: Mediterranean (Italy).

Reported from Greece by Simboura and Zenetos (2005). Type locality: Mediterranean (Sicily).

Specimens of Fabricia filamentosa Day 1963 from Greece (Simboura 1990) and the Adriatic (Giangrande and Castelli 1986) were re-examined by Fitzhugh et al. (1994) who described two new species based on this material: Pseudofabriciola analis from the Adriatic and Pseudofabriciola longipyga Fitzhugh, Giangrande & Simboura, 1994 from Greece. Pseudofabriciola analis was subsequently reported from Greece by Simboura (1996).

Originally described from Greece by Fitzhugh et al. (1994). See remarks under Pseudofabriciola analis Fitzhugh, Giangrande & Simboura, 1994.

Questionable status. Species complex. Salazar-Vallejo (2017) revised the genus Brada and transferred a large number of species (including Brada villosa) to Bradabyssa Hartman, 1967. Previous descriptions of Bradabyssa villosa by e.g. Fauvel (1927), comprise a wide variety of characters and probably comprise more than one species under this name (Salazar-Vallejo 2017). Likewise, molecular analyses by Carr et al. (2011) revealed at least two putative cryptic species in Canadian waters (one in the Arctic, another in the Pacific Ocean) which were initially identified as Bradabyssa villosa. Salazar-Vallejo (2017) restricts Bradabyssa villosa sensu stricto to the North Atlantic Ocean and European and Russian Arctic and re-instates Bradabyssa parthenopeia (Lo Bianco, 1893) from the Mediterranean (Gulf of Naples) – a species previously considered a synonym of Bradabyssa villosa. It is highly likely that Bradabyssa villosa is absent from the Mediterranean and specimens from this region belong to other species such as Bradabyssa parthenopeia.

Questionable status. One specimen from Greece in the collections of the Senckenberg Museum (SMF 11285, 39°09'46.8"N, 19°26'21.6"E, 1008 m depth, coll. date 1993-05-19, det. D. Fiege). In the Mediterranean also reported from the Adriatic, but records are considered doubtful by Mikac (2015) based on the Arctic and Subarctic distribution of the species.

Species complex. Consists of at least two different putative cryptic species in the Arctic Ocean (Carr et al. 2011), specimens from other locations could belong to either of these or to a different cryptic species. Salazar-Vallejo (2012) considers the distribution of Flabelligera affinis to be restricted to “Arctic to cold and temperate, boreal localities” and questions the identity of specimens reported under this name from warm water localities such as Africa or Panama. Whether the Mediterranean is considered here temperate or warm water and whether the species occurs in the Mediterranean is unknown; it is considered here to be present in the Greek waters pending further information.

Type locality: Mediterranean.

Questionable status. Salazar-Vallejo (2014) revised the genus Pherusa and re-instated a number of species, many of which were previously considered synonyms of Pherusa plumosa. He restricts Pherusa plumosa in its diagnosis and distribution; currently it is believed to occur in the Arctic and temperate Atlantic Ocean and to be absent from the Mediterranean. The three currently known species of Pherusa occurring in the Mediterranean Sea – previously all grouped under the name Pherusa plumosa – are Pherusa incrustans Quatrefages, 1866, Pherusa mikacae Salazar-Vallejo, 2014 and Pherusa obscura Quatrefages, 1849. As the description by Fauvel (1927) is very general and includes a large range of characters which correspond to Pherusa plumosa sensu stricto, Pherusa obscura and Pherusa incrustans (Salazar-Vallejo 2014), all specimens identified using Fauvel’s key are questionable.

Type locality: Mediterranean (Gulf of Naples)

Salazar-Vallejo (2011) revised the genus Stylarioides and reinstated Stylarioides hirsutus Lo Bianco, 1893, which Fauvel (1927) had synonymised with Stylarioides monilifer. Thus, specimens identified using the publication by Fauvel (1927) or works based on it (e.g. Castelli 1990) could belong to either of the two species. Type locality: Mediterranean (Gulf of Naples).

Questionable status. Salazar-Vallejo (2013) restricts Therochaeta flabellata to the North-East Atlantic Ocean and Arctic waters and assigns Mediterranean material, including the description by Fauvel (1927) to an undescribed species (informally named Therochaeta cf. flabellata “Mediterranean”, formal description pending). The Mediterranean form differs from the original description mainly in the size of the much larger sediment particles and in the lack of fusion of the first two chaetigers.

Böggemann (2002) distinguishes the species from Glycera tridactyla Schmarda, 1861, mainly on the basis of the shape of the proboscidial papillae and ailerons; although the separation was judged problematic by Worsfold (2007). Parapar and Moreira (2015) agree in separating the two species on the basis of the above two characters.

Frequently reported from the Mediterranean (e.g. Castelli et al. 2008, Ayari et al. 2009, Çınar et al. 2014, Mikac 2015), but Böggemann (2002) and Böggemann (2015) restricts its distribution to Arctic, Antarctic, cold temperate areas and deep sea down to 5655m (Böggemann 2015). The Mediterranean material could possibly be Glycera lapidum Quatrefages, 1866 or Glycera noelae Böggemann, Bienhold & Gaudron, 2012 (Böggemann, pers. comm.)

Böggemann (2002) synonymised Glycera dayi O' Connor, 1987 with Glycera celtica but this synonymy has not been accepted unanimously (Worsfold 2007, Parapar and Moreira 2015).

O'Connor (1987) reports at least four varieties amongst the examined material from the North-East Atlantic, although these correspond in fact to different species (Böggemann, pers. comm.).

Böggemann (2002) considers Glycera rouxii a synonym of Glycera unicornis Lamarck, 1818 (based on comparisons with original description as the holotype is lost). He considers the shape of the retractable branchiae (reported as bifid in Glycera unicornis) not to be a diagnostic character, since variations were found in the same populations (Böggeman, pers. comm.). However, Worsfold (2007) and Parapar and Moreira (2015) debate this synonymy and highlight differences in parapodial lobes besides those of the branchiae, although parapodial lobes were found to change between juvenile and adult specimens by Böggemann (2002). They propose that the branchial shape remains a diagnostic character, which should however be used with caution due to retractability. Despite the available evidence for the synonymy, two recent works consider both species as valid. Therefore, the past records of Glycera rouxii in Greece (see Supplementary material) are currently retained as separate, until a response to the arguments of Parapar and Moreira (2015) is available. Type locality: Mediterranean (Marseille).

Type locality: Mediterranean (Croatia).

Böggemann (2002) considers Glycera convoluta a synonym of Glycera tridactyla based on comparisons with the original description and illustrations. A number of authors support this synonymy (e.g. Worsfold 2007, Parapar and Moreira 2015).

See notes under Glycera rouxii Audouin & Milne Edwards, 1833.

Reported from Greece by Simboura (2008). In the Mediterranean also known from Israel (Böggemann 2005), Egypt (Ben-Eliahu 1972a) and Turkey (Çınar et al. 2014). Originally described from Bonhoure (Djibuti).

Type locality: Mediterranean (Nice, France).

Reported from Greece by Böggemann (2005) from material collected by E. Marenzeller in 1894 on the Cyclades plateau (as Goniada emerita Audouin & Milne Edwards, 1833). In the Mediterranean also known from Spain and France (Böggemann 2005). Otherwise reported from the West and East Atlantic and North-East Pacific (Böggemann 2005).

Reported from Greece by Böggemann (2005) from the abyssal zone (3848 m) off the Peloponnese. In the Mediterranean also known from Spain, Italy and Israel (Böggemann 2005), otherwise reported from the Eastern Atlantic and the Indian Ocean (Böggemann 2005).

In the Mediterranean only reported from Greece (Arvanitidis 2000a). Commonly distributed in the Black Sea (Annenkova 1929) and around the North-East Atlantic (Wolff and Stegenga 1975, Kirkegaard 2001).

Reported from Greece by Bogdanos and Satsmadjis (1983) and Bogdanos and Satsmadjis (1987). In the Mediterranean also known from Israel (Böggemann 2005), otherwise reported from the North-West Atlantic, East Atlantic and South-West Indian Ocean (Böggemann 2005).

Type locality: Mediterranean (France).

Hesione species display a high colour variability and it is currently unknown whether these are colour morphs of the same species or belong to different species (Mikac 2015, Jimi et al. 2017). For this reason, the status of Hesione pantherina, Hesione splendida and similar species is still unclear; here we follow the opinion of F. Pleijel (pers. comm. to Mikac 2015) and list occurrences of Hesione pantherina under Hesione splendida.

Schmidt and Westheide (2000) assess the genetic differentiation of worldwide Hesionides arenaria populations. Specimens from Crete group with those from near the type locality in the North Sea, indicating the presence of Hesionides arenaria sensu stricto in Greece.

Species complex. Schmidt and Westheide (1999) recover three genetic lineages from worldwide localities which could correspond to cryptic species. Specimens from Crete group with those from near the type locality in the Red Sea, indicating the presence of Hesionides gohari sensu stricto in Greece.

Frequently reported from Greece, considered cosmopolitan (Pleijel 2004). Simboura (1996) notes morphological differences between specimens of Hesiospina similis from the Mediterranean and from the native range (Japan). Specifically, Mediterranean material exhibits a stronger serration of the blades of the compound chaetae and neuropodial aciculae with rounded instead of tapering tips.

Reported by von Marenzeller (1902) from deep waters (808 m) off Milos. Marenzeller's two specimens (Natural History Museum Vienna, Inv. No. 599, Acq. No. 15503) were examined by S. Faulwetter. One specimen was confirmed as Leocrates atlanticus; in the second specimen the jaws could not be observed without dissection and its identity is not confirmed.

Synonymised by Hartman (1965a) with Leocrates chinensis Kinberg, 1866, Leocrates claparedii was reported under the former name for several years (see also remarks in Table 1), therefore listed in inventories of non-native species in the Mediterranean (e.g. Zenetos et al. 2010). Pleijel (1998), in his revision of the Hesionidae, considers the two species distinct. Type locality: Mediterranean (Gulf of Naples).

Questionable status. Reported from Greece by Akoumianaki and Hughes (1997), also found by Papageorgiou et al. (2006) (unpublished data), but Microphthalmus aberrans is a taxonomically confused species. Riser (2000) revised the species and found the slides of the type material to be comprised of two different species. He assigned specimens previously assigned to Microphthalmus aberrans to three species: Microphthalmus aberrans, Microphthalmus pettiboneae Riser, 2000 and Microphthalmus aggregatus Riser, 2000. However, the species re-described as Microphthalmus aberrans by Riser does not resemble previously available descriptions of the species, as those were mostly copied from a re-description by Southern (1914), which was based on the wrong microscope slide. The specimen on this slide was re-described as Microphthalmus pettiboneae by Riser, causing confusion in the application of the name Microphthalmus aberrans. All specimens reported under this name would need to be re-investigated to clarify their identity.

Reported from Greece by Koukouras (1979), also found by Papageorgiou et al. (2006) (unpublished data). In the Mediterranean also known from Italy (Castelli et al. 2008), otherwise distributed in the Black and North Seas.

Reported from Greece by NCMR (1995) and NCMR (2000a). In the Mediterranean also known from Spain (Capaccioni-Azzati and Torres-Gavila 1989), otherwise distributed along the Atlantic coast of the Iberian Peninsula.

Reported from Greece by Dando et al. (1995). In the Mediterranean also known from Egypt (Dorgham et al. 2013), otherwise distributed in the Black Sea, North Sea and East coast of North America.

New record for Greece. One specimen, Elafonisi, Crete, 35°16'20.7"N, 23°32'15.9"E, 1 m depth, fine sand, collected in the framework of the MEDCORE project (unpublished data from Papageorgiou et al. 2006). Literature used for identification: Zunarelli (1967), Sordino (1990). Type locality: Mediterranean (Leghorn coast, Italy).

Reported from Greece by Chatzigeorgiou et al. (2016). Type locality: Mediterranean (Banyuls-sur-Mer, France).

Questionable status. Pleijel et al. (2012) consider the status of the species in the Mediterranean doubtful, as no specimens could be recovered from typical habitats despite intense sampling. Based on examination of other specimens, the authors conclude that the species is probably restricted to boreal regions. Records from the Adriatic and the Sea of Marmara are likewise considered questionable by Mikac (2015) and Çınar et al. (2014) respectively.

Questionable status. Reported from Greece by Nicolaidou et al. (1990). Type locality: Mediterranean (Martinscica, Adriatic). While it is possible that the species occurs in Greece, it has so far only been reported in grey literature and has not been found in over three decades, therefore its presence in Greece is here considered questionable.

Type locality: Mediterranean (Gulf of Naples).

Type locality: Mediterranean (Port-Vendres, France).

May have been confused with Podarkeopsis galangaui Laubier 1961 or Podarkeopsis arenicolus (La Greca, 1946), both native to the area but not included in any keys for the region and therefore probably underreported (Pleijel 2005). Reported from the Mediterranean, European Atlantic coasts and South Africa, considered questionable in Turkey by Çınar et al. (2014).

Reported from Greece by Arvanitidis (1994) based on a single specimen. Type locality: Mediterranean (Banyuls-sur-Mer, France). Pleijel (1998) considers the species a junior synonym of Podarkeopsis arenicolus (La Greca, 1946) but does not provide details and does not formalise the synonymy. As Rizzo and Salazar-Vallejo (2014) list both species in their key and recognise difference in the size of the eyes, length of the median antenna and chaetal details, the species is therefore treated as valid here, pending further information.

Questionable status. Reported from Greece by Antoniadou and Chintiroglou (2005) from a benthic sample of hard substrates at 3–15 m depth collected via SCUBA diving. No description or further information was provided for the taxon. Iospilidae are holopelagic and easily confused with benthic juvenile forms of other species (Jiméz-Cueto et al. 2006). Thus the record is considered doubtful here.

Originally described from the Hellenic Trench (Matapan deep; 35°49'48"N, 22°20'42"E; 4690 m depth), no other records from Greece.

Type locality: Mediterranean (Gulf of Marseille).

Type locality: Mediterranean (Algiers Bay).

Reported from Greece by Wesenberg-Lund (1939a). Widely distributed in the Mediterranean (Wesenberg-Lund 1939a).

Reported from Greece by Wesenberg-Lund (1939a); three additional specimens in the Senckenberg collection management system (Cat. No. 11278, 34°26'41.4"N, 26°06'34.2"E, 4255–4308 m; Cat. No. 11279, 35°48'57.6"N, 25°15'46.8"E, 1875–1877 m, Cat. No. 11280, 35°50'23.4"N, 25°16'08.4"E, 1876 m, all det. D. Fiege). Type locality: Mediterranean.

Reported from Greece by Wesenberg-Lund (1939a); one additional specimen from Greece in the collections of the Natural History Museum London (NHM 1968.52, 37°49'02"N, 19°45'06"E, 0-500 m depth, det. N. Tebble). Type locality: Mediterranean (Gulf of Naples).

Reported from Greece by Wesenberg-Lund (1939a). Lopadorrhynchus nationalis is often listed in the literature as a synonym of Lopadorrhynchus brevis Grube, 1855, but Dales and Peter (1972) point out differences between the two species and consider them distinct. Widely distributed in the Mediterranean (Wesenberg-Lund 1939a).

Reported from Greece by Wesenberg-Lund (1939a). In the Mediterranean also known from Italy (Castelli et al. 2008) and the Adriatic (Mikac 2015), otherwise cosmopolitan in pelagic waters (Dales and Peter 1972).

Reported from Greece by NCMR (1989). Type locality: Mediterranean (Bay of Algiers).

One specimen from Greece in the collections of the Senckenberg Museum (SMF 11264, 35°50'40.8"N, 22°19'49.8"E, 4754–4766 m, coll. date 1993-05-25, det. D. Fiege). In the Mediterranean also known from Italy (Castelli et al. 2008) and the Adriatic (Mikac 2015). Present in the adjacent Sea of Marmara (Çınar et al. 2014). Otherwise cosmopolitan in pelagic waters (Dales and Peter 1972).

Reported from Greece by Katsiaras et al. (2017). In the Mediterranean also known from the central and western basins (Bertasi et al. 2014, Gómez et al. 2015, Mikac 2015, D’Alessandro et al. 2016). Its presence in the region was probably overlooked until its description.

Type locality: Mediterranean (Adriatic).

Type locality: Mediterranean (Adriatic). Carrera-Parra (2004) redefined the genus, including Lumbricalus adriatica, using the maxillary apparatus in combination with chaetal types for differentiating species.

Questionable status. Reported from Greece by Dounas (1986). The record refers to Lumbrinerides acuta sensu Ramos 1976. The original description by Verrill (1875) is not detailed, but the redescription by Perkins (1979) based on specimens collected in the type locality (Rhode Island, USA) includes an accessory tooth on maxillary pair MI. The absence of an accessory tooth, as it is described in Ramos (1976), may indicate an undescribed species (Gómez et al. 2015). In the Mediterranean also known from Spain (Sardá et al. 1999), Italy (Castelli et al. 2008), Turkey (Çınar et al. 2014) and the Adriatic (Mikac 2015), but it is unclear whether these records refer to specimens having an accessory tooth or not. While it is possible that the species occurs in Greece, it has so far only been reported in grey literature and has not been found in over three decades, therefore its presence in Greece is here considered questionable.

In the Mediterranean known from Greece, Turkey (Çınar et al. 2014) and Cyprus (Çınar 2005), otherwise distributed along the Atlantic coast of Europe.

New record for Greece. Two specimens, Pachia Ammos, Crete, 35°06'39.6"N, 25°48'32.4"E, 1–5 m depth, fine to coarse sand, collected in the framework of the MEDCORE project (unpublished data from Papageorgiou et al. 2006). Literature used for identification: Ramos (1976). Type locality: Western Mediterranean.

In the Mediterranean only reported from Greece (Simboura and Zenetos 2005). Known from deep waters off the Atlantic coast of Europe.

New record for Greece. One specimen, Elafonisi, Crete, 35°16'20.7"N, 23°32'15.9"E, 1 m depth, fine sand, collected in the framework of the MEDCORE project (unpublished data from Papageorgiou et al. 2006). Literature used for identification: Miura (1980), Gravina and Cantone (1991). In the Mediterranean also known from Italy (Gravina and Cantone 1991). Originally described from South Africa.

Type locality: Mediterranean. Carrera-Parra (2006) considers records from outside the Mediterranean Sea doubtful.

Questionable status. Reported from Greece by Arvanitidis (2000a) and Kitsos (2003); the first Mediterranean record was by Giangrande et al. (1981). Arvanitidis (2000a) argues that the species may have been underreported in the Mediterranean due to its similarity with Lumbrineris coccinea (Renier, 1804). Carrera-Parra (2006) and D’Alessandro et al. (2016) consider Mediterranean records of the species doubtful based on its otherwise East Pacific distribution. Çınar (2009) argues that the description and illustrations of Lumbrineris inflata by Giangrande et al. (1981) fit the characters of Lumbrineris perkinsi Carrera-Parra, 2001. Lumbrineris inflata differs from Lumbrineris perkinsi mainly in the number of teeth of maxilla III (M III). Giangrande et al. (1981), as well as Arvanitidis (2000a) for Greece, report a maxillary formula which could correspond to Lumbrineris perkinsi ("M III with 3–4 teeth"). Although published descriptions and records from the Mediterranean indicate the presence of Lumbrineris perkinsi, re-examination of all the material is needed to draw conclusions about the identity of the Greek records.

Frequently reported from Greece, however, mainly on the basis of external and unreliable diagnostic characters. Species descriptions focusing on the maxillary apparatus and other unambiguous and size-independent characters have recently become available (Carrera-Parra 2006, Martins et al. 2012, D’Alessandro et al. 2016). Therefore, re-examination of material could reduce the frequency of records and even reveal the presence of overlooked species. In the Mediterranean, the species is widely recorded (e.g. Campoy 1982, Çınar 2005, Castelli et al. 2008, Ayari et al. 2009, Çınar et al. 2014, Mikac 2015). Otherwise distributed in the North-East Atlantic; its presumed cosmopolitan distribution is questionable (Carrera-Parra 2006).

New record for Greece. Specimens previously reported as as Lumbrineris cingulata Ehlers, 1897 by Chatzigeorgiou et al. (2016) from rocky shores in northern Crete were re-examined and found to belong to Lumbrineris luciliae as described by Martins et al. (2012), although the reported slight distal curvature of the aciculae could not be observed. In the Mediterranean also known from Italy (D’Alessandro et al. 2016). Otherwise known from the Atlantic coast of the Iberian Peninsula (Martins et al. 2012).

Type locality: Mediterranean (Baie de Rosas, Spain). Lumbrineris nonatoi has several diagnostic characters in common with the – later described – Gallardoneris iberica Martins, Carrera-Parra, Quintino & Rodrigues, 2012. Due to this confusion, Bertasi et al. (2014) and Katsiaras et al. (2017) suggest that several literature records of Lumbrineris nonatoi could belong to the overlooked Gallardoneris iberica, although the overall presence of the former in the region has not been doubted.

Questionable status. Reported from Greece as Ninoe kinbergi by Vamvakas (1970) and Vamvakas (1971). Arvanitidis (2000a) lists these records under the name Ninoe nigripes, following the synonymy established by Pettibone (1963). In the Mediterranean reported from the central basin as Ninoe kinbergi (Castelli et al. 2008) and as Ninoe nigripes by Mikac (2015) from the Adriatic Sea. Otherwise distributed in the West Atlantic.

Questionable status. Reported from Greece by Dando et al. (1995) and Akoumianaki (2004). The record by Akoumianaki (2004) actually refers to Scoletoma emandibulata mabiti, as Ramos 1976 is given as the authority; it remains unclear whether the same holds true for the specimen of Dando et al. (1995). Originally described from the Indian Ocean.

Type locality: Mediterranean (Catalan Coast).

Species complex. Frequently reported from Greece and other parts of the Mediterranean (Castelli et al. 2008, Ayari et al. 2009, Çınar et al. 2014, Mikac 2015). Otherwise distributed in the Atlantic Ocean, Arctic Ocean and North Sea. However, molecular analyses revealed the existence of at least two putative cryptic species, one in the Atlantic and one in the Arctic Ocean (Carr et al. 2011).

In the Mediterranean also known from the western and central basins (Campoy 1982, Castelli et al. 2008), Tunisia (Ayari et al. 2009), Turkey (Çınar et al. 2014) and the Adriatic (Mikac 2015). Otherwise distributed in the North-East Atlantic. However, Oug (2011) noted that Scoletoma funchalensis is poorly known and the described characters by Fauvel (1923) could be confused with juveniles of several species.

Type locality: Mediterranean (Gulf of Naples). George and Hartmann-Schröder (1985) synonymised Scoletoma impatiens with the South African Scoletoma tetraura (Schmarda, 1861), but several authors do not accept this synonymy (see also notes under Scoletoma tetraura).

Questionable status. Reported from Greece by Dounas (1986). Type locality: Mediterranean (Adriatic). While it is possible that the species occurs in Greece, it has so far only been reported in grey literature and has not been found in over three decades, therefore its presence in Greece is here considered questionable.

Questionable status. Reported from Greece by Koukouras and Rousso (1991). In the Mediterranean also known from Turkey (Doğan et al. 2005; but considered questionable by Çınar et al. 2014), Cyprus (Çınar 2005), Italy (Castelli et al. 2008), Albania (Marzano et al. 2010) and the Adriatic (listed under Scoletoma impatiens (Claparède, 1968) by Mikac (2015)). Originally described from South Africa. George and Hartmann-Schröder (1985) synonymised the European species Scoletoma impatiens with Scoletoma tetraura. However, several authors question the presence of the latter in Europe and suggest using the name Scoletoma impatiens for specimens from the area until a more detailed revision becomes available (Martins et al. 2012, Çınar et al. 2014, Gómez et al. 2015, Mikac 2015, D’Alessandro et al. 2016). The main diagnostic character of the genus can be problematic, since several juvenile specimens of Lumbrineris and Hilbigneris species may lack composite hooded hooks and can be key out as Scoletoma (Oug 2011).

Reported from Greece by Dounas (1986) and Arvanitidis (1994). In the Mediterranean also known from France (Fiege et al. 2000b), Italy (Castelli et al. 2008), Turkey (Çınar et al. 2014) and the Adriatic (Mikac 2015). Probably underreported, since older records of Magelona cincta Ehlers, 1908 may belong to Magelona alleni (Wilson 1958; see also notes under Magelona cincta).

Questionable status. Reported from Greece by Zarkanellas (1980) and Makra and Nicolaidou (2000), but specimens probably belong to Magelona alleni Wilson, 1958. Wilson (1958) described Magelona alleni from material misidentified as Magelona cincta and concluded that the latter does not occur in European coasts.

Type locality: Mediterranean (Villefranche-sur-Mer, France).

Probably an underreported species, since older records of Magelona papillicornis F. Müller, 1858 may belong to Magelona mirabilis (Fiege et al. 2000b; see also notes under Magelona papillicornis)

Questionable status. Until 1977, all European magelonids with mucronate chaetae on chaetiger 9 were assigned to Magelona papillicornis, originally described from Brazil. However, Jones (1977) re-described Magelona papillicornis and clarified that it actually lacks this character and therefore questioned its presence in European waters. Fiege et al. (2000b) demonstrated the presence of two species bearing mucronate chaetae on chaetiger 9 in Europe; Magelona mirabilis (Johnston, 1865) and Magelona johnstoni Fiege, Licher & Mackie, 2000. Greek records of Magelona papillicornis could belong to either of these, although only Magelona mirabilis has been recorded up to now.

One specimen from Greece in the collections of the Senckenberg Museum (SMF 11286, 39°15'0.6"N, 23°42'32.4"E, 1243 m, coll. date 1998-01-01, det. D. Fiege). In the Mediterranean also known from the coasts of France and Spain (Labrune et al. 2007, Serrano-Samaniego 2012) and the Adriatic (Mikac 2015).

Type locality: Mediterranean (Gulf of Naples).

Questionable status. Species complex. In the Mediterranean only reported from Greece (Dando et al. 1995). Distributed along the Pacific coast of North America where at least two morphologically indistinguishable forms with different life histories occur (Wilson 1983).

In the Mediterranean only reported from Greece (Simboura 1996). The specimens differ from Clymenella torquata (Leidy 1855) (originally from the East coast of North America but occurring non-natively on the Atlantic coast of Europe) in the shape and number of acicular chaetae and from Clymenella cincta (Saint-Joseph, 1894) (occurring in the Mediterranean) in the shape of the collar and of the nuchal organs. The Greek specimens are most similar to the Pacific species Clymenella koellikeri, from which they differ in the following characters: Nuchal slits of Clymenella koellikeri reach up to the middle of the cephalic plate (until the lateral notches in the Greek material) and the rim or the collar of the 4^th chaetiger is smooth or slightly wavy in Clymenella koellikeri, whereas one Greek specimen shows a small lateral recess at the rim of the collar (Simboura 1996). The species is found regularly in Greece but is usually reported at genus level due to its uncertain identity. It may be an overlooked or cryptic species.

Type locality: Mediterranean (Gulf of Naples).

Type locality: Mediterranean (Palermo, Sicily, Italy).

Reported from Greece by Bogdanos and Satsmadjis (1983) and Xenopoulou (1987). In the Mediterranean also known from France, Spain and Israel (Mackie and Gobin 1993), Egypt (Abd-Elnaby 2008), Turkey (Çınar et al. 2014) and the Adriatic (Mikac 2015), otherwise distributed along the European and North African Atlantic coasts (Mackie and Gobin 1993).

Questionable status. In the Mediterranean only reported from Greece (Papadopoulos 1986). Known from South Africa.

Questionable status. In the Mediterranean only reported from Greece (Bogdanos and Nicolaidou 1985, Bogdanos and Satsmadjis 1987, Nicolaidou and Papadopoulou 1989, Koulouri et al. 2015). Outside the Mediterranean reported from worldwide locations, mostly from bathyal and abyssal depths.

Originally distributed in the Red Sea, the Indian Ocean and the North Pacific; commonly reported from locations throughout the Mediterranean (Simboura and Zenetos 2005). The first Mediterranean record of Metasychis gotoi is from the Northern Adriatic (Fauvel 1940), constituting one of the earliest records of non-native species in the basin. As Metasychis gotoi is reported from worldwide distributions, it is likely that the name refers to a complex of cryptic species. The Mediterranean material could belong to an overlooked native species (J. Langeneck, pers. comm.).

Reported from Greece by Eleftheriou et al. (1990) and NCMR (2000a). In the Mediterranean also known from Israel (Ben-Eliahu 1976b), Spain (Alós 1990), Italy (Gherardi et al. 2002), Egypt (Abd-Elnaby 2008) and the Adriatic (Mikac 2015). Present in the adjacent Sea of Marmara (Çınar et al. 2014). Otherwise distributed along the European Atlantic coasts (Gherardi et al. 2002).

Questionable status. Frequently reported from Greece and other Eastern Mediterranean locations; however, de Assis et al. (2007) in their review of the genus restrict its distribution to boreal regions.

Questionable status. In the Mediterranean only reported from Greece (e.g. Bogdanos and Satsmadjis 1983, Eleftheriou et al. 1990, Tselepides 1992, Simboura 1996; full reference list in Suppl. material 2), de Assis et al. (2007) restrict its distribution to the Shetland Islands.

Reported from Greece by Tselepides (1992). In the Mediterranean also known from France (Clausade 1969), Israel (Ben-Eliahu 1995) and Italy (Castelli et al. 2008), otherwise distributed along the Atlantic coasts of Europe and in the North Sea.

Type locality: Mediterranean (Gulf of Naples).

Species complex. At least three putative cryptic species exist, one each in the Arctic and West Atlantic (Carr et al. 2011) and another in Portugal (Lobo et al. 2016).

Questionable status. In the Mediterranean only reported from Greece (Eleftheriou et al. 1990). Commonly distributed in the North-East Atlantic.

Reported from Greece by Chatzigeorgiou et al. (2016) based on a single specimen. In the Mediterranean also known from Tunisia (Wesenberg-Lund 1939b), France (Laubier and Paris 1962), Italy (Castelli et al. 2008) and the Adriatic (Mikac 2015), otherwise distributed along the Atlantic coasts of Europe (Nygren and Pleijel 2015).

Questionable status. Reported from Greece by von Marenzeller (1902). Marenzeller's description differs from the current concept of Aglaophamus malmgreni in the first branchial chaetiger and the pharyngeal papillation. Marenzeller describes his specimens with branchiae starting at chaetigers 6–7 (in one specimen at chaetiger 10) and states that his specimens correspond to the description of Nephtys malmgreni by McIntosh (1900) (listed by McIntosh under the name Nephtys longisetosa) in the number of papillae. McIntosh describes 15 rows of 11–15 papillae. Branchial and papillation characters correspond to Aglaophamus pulcher (Rainer, 1991), but Marenzeller's material should be examined for confirmation. In the Mediterranean, Aglaophamus malmgreni has also been reported from the Adriatic Sea (Mikac 2015), otherwise it is distributed in circumpolar regions and records from southern Europe require confirmation (Ravara et al. 2010).

Reported from Greece by Arvanitidis (2000a) but specimens of Aglaophamus malmgreni (Théel, 1897) by von Marenzeller (1902) could belong to Aglaophamus pulcher (see notes there). In the Mediterranean also known from abyssal canyons and plains in the western basin (Ravara et al. 2010), otherwise distributed in the North East Atlantic. May have been confused in the past with Nephtys hystricis McIntosh, 1900 and Nephtys incisa Malmgren 1865 (Rainer 1991) and therefore been overlooked in the area.

Questionable status. Ravara et al. (2010) found morphological differences between European specimens identified as Inermonephtys inermis and the holotype from Florida and established a new species, Inermonephtys foretmontardoi Ravara, Cunha & Pleijel, 2010 for the European populations. Inermonephtys inermis is restricted to the West Atlantic. It is highly likely that Greek specimens of Inermonephtys inermis belong to Inermonephtys foretmontardoi, but no specimens have been re-examined yet for confirmation.

Ravara et al. (2010) regard the presence of the species in the Mediterranean as doubtful due to its otherwise Indo-Pacific distribution. Greek specimens may also have been confused with Micronephthys stammeri (Augener, 1932) in the past.

Type locality: Mediterranean (Micronephthys maryae: Ibiza, Micronephthys stammeri: Adriatic).

Rarely reported from the Mediterranean, but was considered a synonym of Nephtys hombergii Savigny in Lamarck, 1818 until its resurrection and redescription by Rainer (1989) and could therefore be underreported.

Ravara et al. (2010) re-examined material from the Mediterranean and identified it as Nephtys caeca, concluding that, although the species is commonly distributed in Arctic waters, it occasionally occurs in warmer waters of the Mediterranean as far as the Black Sea.

Questionable status. Reported from Greece by Vamvakopoulou (1991). In the Mediterranean also reported from the western basin (Fredj 1974) and the Adriatic (Mikac 2015). Commonly distributed in boreal areas; Mediterranean records require confirmation (Ravara et al. 2010).

Type locality: Mediterranean (Gulf of Naples).

The description of Nephtys hystricis by Fauvel (1923) actually refers to Nephtys incisa Malmgren, 1865 and vice versa (Rainer 1990). Thus, specimens identified as Nephtys hystricis using Fauvel's key and description probably belong to Nephtys incisa. Both Nephtys incisa and Nephtys hystricis have been reported from Greece, thus they can both be considered as present, despite this confusion.

See notes under Nephtys hystricis McIntosh, 1900.

Fauvel (1923) considered Nereis lamellosa Ehlers 1868 a synonym of Nereis succinea but revoked this synonymy in a subsequent publication, describing the differentiating characters (Fauvel 1936b). Later authors (e.g. Day 1967, Campoy 1982) continued to treat the species as synonymous. Thus, many reports of Alitta succinea may actually contain specimens of Nereis lamellosa, which in turn is probably underreported in the Mediterranean (Arvanitidis 2000a).

Questionable status. Species complex. In the Mediterranean only reported from Greece (Christomanos and Giannitsis 1962). Distributed in the North Atlantic and North Pacific and comprising at least two cryptic species with genetic and morphological differences in these two areas (Carr et al. 2011).