Marine Bryozoa of Greece: an annotated checklist

Abstract Background Until today, a complete checklist of Bryozoa of the Greek seas had never been published and species records were scattered in several taxonomic and ecological studies. The aim of this paper is to produce a first checklist of marine bryozoan species of Greece, in the framework of the Greek Taxon Information System (GTIS) initiative of the LifeWatchGreece Research Infrastructure (ESFRI), by reviewing the existing literature and following the recent trends in the taxonomy of this group. ﻿ New information The marine bryozoan fauna of Greece comprises 237 species, classified in 127 genera, 66 families, 3 orders, and 2 classes. The vast majority belongs to the class Gymnolaemata (177 Cheilostomatida and 21 Ctenostomatida), while the remaining 39 species are Stenolaemata (all Cyclostomatida). Among these species, 12 are considered endemic to the eastern Mediterranean, while another 12 species are non-indigenous.


Introduction
The Mediterranean bryozoan fauna represents about 9.6% of the known global diversity of Bryozoa (Rosso and Di Martino 2016). However, current knowledge on the bryozoan fauna of this basin is highly biased due to differences in research effort for different taxa, marine areas and habitat types. Recent efforts in the south-eastern Mediterranean Sea have significantly increased our knowledge from areas which were previously considered "datapoor" spots for bryozoans, revealing a considerable proportion of non-indigenous taxa (e.g. Harmelin et al. 2016, Sokolover et al. 2016. Furthermore, information on Bryozoa from several Mediterranean areas is fragmented in old publications and grey literature; the collation of updated checklists (e.g. Koçak and Aydın Önen 2014) by experts could contribute to the mapping of diversity for understudied taxa and areas (Bailly et al. 2016, this special collection).
Sporadic records of bryozoans from the Aegean Sea can be found in old taxonomic studies, including the descriptions of the cheilostome species Calpensia nobilis, Hippaliosina depressa and Watersipora cucullata from this marine region (Busk 1854), based on material collected from shallow water macroalgae by E. Forbes. The first studies focusing on Bryozoa of the eastern Mediterranean basin, the Greek seas included, took place in the late 1960s (Harmelin 1969), based on material that was collected with dredges during the oceanographic expedition of the French research vessel "Jean Charcot" (1968). A total of 101 species belonging to all the 3 living bryozoan orders, were found, including several new records for the Mediterranean fauna. Later, the taxonomic study by Hayward (1974) on the cheilostome Bryozoa of Chios Island (north-eastern Aegean) yielded 101 species, including rare records and new species. Sharing only 47 cheilostomes with Harmelin's list mentioned above, this study increased the eastern Mediterranean bryozoan diversity by 54 species.

Materials and methods
The checklist presented in this paper was compiled in the framework of the Greek Taxon Information System (GTIS), an initiative of the LifeWatchGreece Research e-Infrastructure aiming to produce a complete inventory of the known biodiversity of Greece (Bailly et al. 2016, this special collection). As this is the first attempt to compile a checklist of bryozoan diversity of the Greek seas, we performed an exhaustive literature review of bryozoan records. All taxa were cross-checked for synonymies and dubious records against the World List of Bryozoa (recent and fossil), the World Register of Marine Species (Bock and Gordon 2016, WoRMS Editorial Board 2016), and the recent update of the Mediterranean bryozoan diversity by Rosso and Di Martino (2016). Taxa identified as cf., as well as those left in open nomenclature, and fossil records were not included in the list. The checklist is annotated with the literature references reporting the presence of each species from Greek waters, as well as with notes on the nomenclature of some taxa. Non-indigenous bryozoans are also marked (NIB). The checklist follows the alphabetical order.
All species included in the checklist are recognized in the World List of Bryozoa and the World Register of Marine Species, except for three of them. These are: Idmidronea triforis (Heller, 1967) and I. coerulea Harmelin, 1976, allocated within the genus Idmidronea Canu and Bassler, 1920and not Exidmonea David, Mongereau and Pouyet, 1972'Microecia' occulta (Harmelin, 1976), provisionally left in its former allocation because the characters of the species differ from those of the genus Oncousoecia Canu, 1918 that has been suggested for its allocation (although Microecia Canu, 1918 is recognized as a synonym of Plagioecia Canu, 1918). The taxon Rhynchozoon sp. 1 sensu Hayward, 1974 described from Chios Island, was retained in the checklist following extensive lists by Zabala and Maluquer 1988, Rosso and Di Martino 2016 and taxonomic papers with description and illustrations of material from Tyrrhenian and Adriatic localities (Chimenz Gusso et al. 2014).
A number of taxa were omitted from the present checklist (Table 1) for different reasons: (1) taxa now recognized as species complexes and considered absent from the Mediterranean; further examination of specimens is needed to ascertain their correct identification; (2) species whose currently accepted geographic distribution does not include the Mediterranean Sea; the examination of the material with the Scanning Electron Microscope could possibly raise the number of non-indigenous species in the Mediterranean basin; (3) species known exclusively as fossils from Tertiary sediments of Europe, whose persistence in the Mediterranean Sea throughout the Messinian Salinity Crisis needs to be ascertained.

Discussion
The bryozoan fauna of the Greek seas makes up 42.7% of the species, 59.9% of the genera and 71% of the families of the Mediterranean bryozoan fauna, specifically 41.7% of the Cheilostomatida, 36.8% of the Ctenostomatida and 52% of the Cyclostomatida species, based on the recent update by Rosso and Di Martino (2016). Despite the small number of sporadically distributed studies on this phylum in Greece, a considerable number of bryozoan species has been reported compared to adjacent eastern Mediterranean countries. A total of 185 species has been recorded from Turkey, 139 of which along the Aegean coasts (Koçak and Aydın Önen 2014)  Among the species reported from Greece, 12 are considered endemic to the eastern Mediterranean basin; these are the cheilostomes Adeonella pallasii, Calyptotheca rugosa, Cellepora posidoniae, Hippopodina ambita, Hippoporidra picardi, Monoporella bouchardii, Plesiocleidochasma mediterraneum, Reteporellina delicatula, Retevirgula akdenizae, Smittipora disjuncta, Therenia rosei and Turbicellepora camera. Of these, 5 species were first described from the island of Chios based on material collected by Hayward (i.e. C. rugosa, H. ambita, R. delicatula, T. rosei, and T. camera), H. picardi was described from the Gulf of Thessaloniki, while R. akdenizae was described from the Turkish coasts of the Aegean Sea. The cheilostome Hippaliosina depressa, which was described from the Aegean Sea, is considered more typical of the eastern Mediterranean basin, including the Sicily Strait, the western Ionian and south Adriatic seas (Harmelin et al. 2016 and references therein, AR personal observations). Nevertheless, this species was recorded in a few localities of western Corsica (Calvet 1902, Gautier 1962 and Sardinia (AR and E. Di Martino, personal observations) in the western Mediterranean.
The recent introduction of non-indigenous species, mostly lessepsian migrants, over the last decades, has considerably increased the number of bryozoans occurring in the Mediterranean Sea (Rosso and Di Martino 2016). Studies in the southeastern Mediterranean basin have brought to light a considerable number of NIBs (Harmelin 2014b, , Harmelin et al. 2016, Sokolover et al. 2016, mainly originated from the Red Sea/Indo-Pacific Ocean. Until today, 12 NIBs have been reported from the Greek seas, representing 5% of the bryozoan fauna of Greece and 20% of the Mediterranean NIB fauna; these are the ctenostomes Amathia gracillima and A. verticillata and the cheilostomes Bugula neritina, Bugulina fulva, Crepidacantha poissonii, Crisularia