Description and distribution of three morphotypes of the Eucyclopsserrulatus group (Crustacea, Copepoda, Cyclopoida) from Algerian water bodies

Abstract Background Examination of Eucyclops populations coming from Algerian water bodies and identified as Eucyclopscf.serrulatus showed three morphotypes, based on morphometric characters and microcharacters. Morphotype 1 was the most abundant, collected in the east and the west of Algeria. Morphotype 2 was sampled in the south of the country, characterised by posterolaterally elongated thoracic segments and the fourth thoracic segment bearing cilia on its lateral angles. Morphotype 3 was found in a small temporary pond in the north of the country and was the smallest one. Other differences were observed on surface microcharacters of antenna basipodite, coxopodite and intercoxal plate of the fourth leg. The characters of the most widespread morphotype (morphotype1) were stable in all localities despite the fact that these were located in two geographically separated regions (eastern and western Algeria). New information Three morphotypes of Eucyclopsserrulatus group (Fisher, 1851) (Crustacea, Copepoda, Cyclopoida) from Algerian water bodies were identified. The characters of the most widespread morphotype (morphotype 1) were stable in all localities despite the fact that these were located in two geographically separated regions (eastern and western Algeria).


Introduction
The genus Eucyclops (Copepoda, Cyclopoida) comprises about one hundred species and 15 subspecies (Dussart and Defaye 2006, Alekseev and Defaye 2011, Mercado-Salas and Suarez-Morales 2014).The last revision of the whole genus was done by Lindberg (1957) for African Eucyclops.Several revisions of Eucyclops were published: for Australia by Morton (1990), for Ukraine by Monchenko (1974), for Japan by Ishida (2002), for Mexico by Mercado-Salas and Suarez-Morales (2014) and for Palearctic by Alekseev and Defaye (2011) and Alekseev (2019).The serrulatus group of the cyclopid freshwater genus Eucyclops comprises species having 12-segmented antennules with the three most distal segments possessing a smooth hyaline membrane, caudal rami 3.5-7 times as long as wide with a longitudinal row of spinules along most of the outer edge of each ramus, a strong inner spine on P5 and a number of microcharacters presented on the antennary basipodite and the caudal surface of P4 coxopodite, as described by Alekseev and Defaye (2011).The type species of this genus is Eucyclops serrulatus (Fischer, 1851).This species has been reported from waterbodies around the world (Dussart andDefaye 1985, Dussart andDefaye 2006) and, consequently, it has long been considered a cosmopolitan species until some species that look like Eucyclops serrulatus were separated from it (Dussart 1984, Reid 1995, Ishida 1997, Ishida 1998).Some of these may indeed be valid species; others were forms of Eucyclops serrulatus.Considerable interpopulation variability in E. serrulatus was described; some of them are cryptic taxa and need to be revised (Sukhikh and Alekseev 2015).Eucyclops serrulatus has been observed in the samples collected in Algeria in the Hoggar, south of Tassili n'Ajjer, in Tamanrasset and in Guelma (Roy and Gauthier 1927).The re-description of the type for Eucyclops serrulatus (Alekseev et al. 2006) using molecular-techniques revealed several microcharacters, important for the species identification as ornamentation of antennary (A2) basipodite and the fourth leg (P4) coxopodite with coxal spine.The name 'serrulatus group' is used for the E. serrulatus species complex and it was established by Kiefer in 1928 for a group of tropical species closely related to E. serrulatus ( Alekseev and Defaye 2011).The serrulatus group now includes 17 species and subspecies, which differ from each other in the presence of microcharacters of the antennary basipodite and the P4 coxopodite.The aim of this work is to describe and compare Algerian morphotypes of Eucyclops serrulatus group coming from different localities.

Materials and methods
Several water bodies were sampled in different regions in Algeria.Eucyclops cf.serrulatus (Fischer, 1851) was found in 21 localities (Fig. 1, Table 1).All samples were collected by horizontal trawl at 1 m depth in the near-shore areas using standard plankton net of 50-μm mesh size.Samples were collected by the author.The samples were preserved in 70% ethanol.For the measurements, six females of each population collected from the field were first placed in small Petri dish containing a mixture of alcohol, water and glycerine.Once the water evaporated (1-2 days), body length, relative length of antennules, the fourth and fifth legs and caudal rami were measured (Table 2).The specimens were dissected in concentrated glycerine and put between slide and coverslip in a drop of glycerol.The measurements and the drawings were made using a drawing tube attached to the microscope.The morphotypes were described, based on the habitus and the microcharacters: the ornamentation of antennule (A1) and antennary (A2) basipodite, caudal surface ornamentation of P4 coxopodite and intercoxal plate, using the coding system for microcharacters in Eucyclops proposed by Alekseev et al. (2006).

Eucyclops cf. serrulatus
Localities with occurrences of the three morphotypes
Antennule 12-segmented, reaching middle of first free thoracal somite in morphotypes 1 and 2 and the beginning of the third one in morphotype 3 (Fig. 2a, Fig. 6a), the last three articles with hyaline membrane, the first segment with curved row of spinules at its base; outermost spinules the longest in morphotypes 1 and 2 (Fig. 2c, Fig. 4c).In morphotype 3, the longest ones were between two groups of little spines (Fig. 6c).
P1: inner edge of basipodite with group of long hair only in morphotypes 1 and 2 (Fig. 3 a, Fig. 5a), intercoxal plate with two groups of finest spinules on body of protuberances, only in morphotype 1, external seta of exopodite 3 in all morphotypes with a row of little spinules along outer margin and with long setules on inner edge (Fig. 3a, Fig. 5a, Fig. 7 a).
P4, innermost apical spine of endopodite 3 was 1.3-1.4times as long as outermost apical spine in all morphotypes and about 1.5-1.6 times as long as supporting segment in morphotype 1 (Fig. 3b) and as long as supporting segment in morphotypes 2 and 3 (Fig. 5b, Fig. 7b), outer seta long reaching almost the top of outermost apical spine in all morphotypes, two apical setae of exopodite 3 stylet-shaped only in morphotype 1 (Fig. 3b), inner edge of basipodite with group of long setules only in morphotypes 1 and 3 (Fig. 3b, Fig. 7b).Coxopodite with a row of numerous fines spinules along internal distal side only in morphotype 1, several groups of spinules: all morphotypes, intercoxal plate with dense setules, in all morphotypes, but in morphotypes 2 and 3, setules are two times longer than those in morphotype 1.On body of plate, I found two groups of little setules and spinules in morphotype 1, two groups of little spinules in morphotype 2 and one group of little setules in morphotype 3. Caudal setae had dense long setules, but those of morphotypes 1 and 3 had a strong spine.

Distribution
This taxon was discovered in the mid-nineteenth century in a pond at Peterhof close to Saint Petersburg, Russia (Fischer 1851).In recent years, the distributional area of the species was revised and restricted to a Palearctic distribution.Previous data on geographical distribution of the species outside this area are critically analysed.It is hypothesised that records of E. serrulatus from Japan, Australia, North America and other zoogeographical zones could be a result of recent invasions, possibly via human activities in relation to ship transport.

Taxon discussion
Eucyclops serrulatus (Fischer, 1851) has been reported from waterbodies around the world and, consequently, it has long been considered a cosmopolitan species until some species that look like Eucyclops serrulatus were separated from it.Some of these may indeed be valid species; others were forms of Eucyclops serrulatus.

Discussion
In Algeria, I identified three morphotypes belonging to Eucyclops serrulatus group that differ from the description of Eucyclops serrulatus from the type locality in the microcharacters of the antennary basipodite and of the P4 coxopodite.The characters of the most widespread morphotype (morphotype 1) were stable in all localities despite the fact that these were located in two geographically separated regions (eastern and western Algeria) In twenty-one localities, I did not find Eucyclops serrulatus, while this species has already been mentioned in Algeria by Roy and Gauthier (1927).
In a comparison with other species of Eucyclops serrulatus group from North Africa, I considered Eucyclops serrulatus hadjebensis (Kiefer, 1926), but this latter is characterised by a shorter serra.
Eucyclops agiloides (Sar, 1909) was recorded in Algeria by Defaye et al. (2010).These morphotypes (at least for morphotypes 2 and 3) cannot be attributed to this species, due to the lack of long hair-like spinules in position 1-2 on the posterior surface of antennary basipod; also the "serra" on caudal rami is completely different.P4 intercoxal plate bears long hair-like spinules in these morphotypes, but it is short in Eucyclops agiloides.There was ornamentation of P4 coxopodite with 20-21 spinules (C+D) in this species, but with eight spinules in the morphotypes.
These morphotypes did not cohabit and presented important differences in morphological characters and microcharacters; they could be ascribed to new pseudocryptic species of the Eucyclops serrulatus group, which is in need of urgent revision.

Table 1 .
Occurrences of Eucyclops cf.serrulatus morphotypes in different localities (numbers referred to the localities).

Table 2 .
Female morphometric characters in morphotypes of Eucyclops cf.serrulatus.Description and distribution of three morphotypes of the Eucyclops serrulatus ...