Echinoderes dujardinii Claparède , 1863 ( Kinorhyncha , Cyclorhagida ) : a new record for the kinorhynch fauna of Turkey

Meiobenthic samplings conducted in the framework of a meiobenthos project in the subtidal coastal waters of Sinop Bay, Southern Black Sea revealed the first report of the kinorhynch Echinoderes dujardinii for the marine fauna of Turkey.


Introduction
Representatives of the phylum Kinorhyncha are among the less studied permanent metazoan meiofauna in the world although they have been first recognized in 1841 by Felix Dujardin (Dujardin, 1851).Today, the phylum includes more than 220 described species and 28 genera (Sørensen et al. 2015).They are benthic marine organisms, distributed world-wide from the intertidal to the abyssal zones, mostly inhabiting muddy bottoms (Sørensen & Pardos 2008;Yamasaki & Fujimoto 2014).
The occurrence of kinorhynchs in the marine fauna of Turkey has first been reported by Bacescu (1961).The author recorded Pycnophyes communis Zelinka, 1908 (Pycnophyidae) at the pre-Bosphoric area of the Black Sea and Çınar (2014) also mentioned the report of this species in his review about the species diversity of several phyla from the coasts of Turkey.Recently, Sönmez et al. (2016) recorded and described two echinoderid species, viz.Echinoderes aff.bispinosus and Echinoderes aff.gerardi from the Aegean Sea.The present study constitutes the third record of this genus in Turkey and stands as the first report of Echinoderes dujardinii Claparède, 1863 from the Turkish coastal waters.

Material and Methods
Kinorhynch specimens were collected by scuba diving at a location with 4 meters water depth in Sinop Bay, Southern Black Sea (Fig. 1) in November 2015.Sediment samples were obtained from soft bottoms (very fine gravel) of the bay by metal push cores (12.56 cm 2 mouth area) and preserved with 75% ethanol on board.In the laboratory, sediments were washed and screened through 500 and 63 µm mesh sieves to separate macrofauna and meiofauna and afterwards stained with Bengal Rose solution.Meiobenthic organisms were sorted under a Nikon SMZ 745 stereo microscope using modified Bogorov chambers.Specimens belonging to major taxa were collected separately by glass pipettes in 2 ml vials containing 75% ethanol.Kinorhynch specimens were examined and photographed using an Olympus BX51 microscope equipped with differential interference contrast (DIC) optics and an Olympus DP70 camera.
Introvert.None of the specimens obtained had the introvert extended, so no information can be given on the mouth cone, oral styles and the structure and arrangement of scalids.
Neck.The neck is formed by 16 cuticular plates named placids, radially arranged and articulated directly with the first segment of the trunk.All placids have a trapezoid shape and are approximately equal in size, except for the midventral one, wider and slightly extended distally (Figs.2A, 3A, 4A).Some of the placids bear additional plates, the trichoscalid plates, on which the trichoscalids of the last scalid ring articulate (Fig. 3A).The cuticle between adjacent placids is soft and appears folded, sometimes mistakenly named as interstitial placids.Trunk.The trunk is divided into 11 segments.As a diagnostic character of the genus, the two first segments are closed rings of cuticle (Fig. 4A).Segments 3 to 11 are formed by a dorsal tergal plate articulated with two ventral sternal plates (Fig. 4A).Hence a ventral view of the animal shows the sternal plates plus a narrow lateral strip of the tergal plate, the so-called lateroventral area.Every segment has an anterior cuticular thickening, the pachycyclus (Figs.2B, 4B) and a posterior edge specialized as a fringe of cuticular tips, the pectinate fringe that overlaps the anterior edge of the next segment.The sizes of the whole trunk and the individual segments agree with the ones reported in the descriptions of the species.The cuticular surface is covered by minute hairs, arising from perforations arranged following characteristic patterns.Other cuticular specializations include sensory spots, glandular cell outlets and cuticular scars marking attachment sites for the underlying musculature.The most important taxonomic feature is the presence, nature and distribution of cuticular appendages, namely spines and tubes (Figs.3A-D).
Tubes occur in lateroventral positions on segment 2; in lateroventral position on segment 5 (Fig. 3A) and in lateral accessory position on segment 8, very close to the lateroventral spine on that segment (Figs. 3B, D).Additionally a laterodorsal tube occur on segment 10. Short middorsal spines occur on segments 4 to 8, slightly increasing in length posteriorly.Spines are located in lateroventral positions on segments 6-9 (Fig. 3D).
Segment 11 (Fig. 3B) bears a pair of big lateral terminal spines, about 150 µm long (Fig. 2A).Additionally, females present one pair of lateral terminal accessory spines nearly 50 µm long.Males have three pairs of flexible penile spines instead.Tergal plate of segment 11 projected posteriorly as one pair of short and pointed tergal extensions.

Discussion
The diversity of the cyclorhagid genus Echinoderes, with more than 80 species, is higher compared to the other kinorhynch genera (Yamasaki & Fujimoto 2014).Species of Echinoderes are commonly found in muddy sediments but they may be observed on algae, sponges and weeds and in sediments containing mud to coarse sand, gravel and shell fragments as well (Sørensen & Pardos 2008, Neuhaus 2013).Echinoderes dujardinii was the first kinorhynch species recorded in the world (Higgins 1983).Originally it was described by Claparéde (1863) and later redescribed by Zelinka (1928) and Higgins (1977).Remane (1928) provided the complex synonymies of the species.The first SEM photos were provided by Sanchez-Tocino et al. (2011).
Echinoderes dujardinii was initially reported from many places all over the world as a mistaken identification of different species of Echinoderes, however its distribution seems to be large covering the Mediterranean and part of the Atlantic Sea.Sanchez-Tocino et al. (2011) reported the species from Mediterranean coast of the Iberian Peninsula.The study of Sanchez et al. (2012) extended the distribution of the species to the Atlantic coasts (South Galicia) of Spain.According to the aforementioned study, the species was found in shallow waters (1.6-18 m) from different sediment types such as shell gravel, coarse sand, sandy mud and mud.Recent comprehensive review of Kinorhyncha by Neuhaus (2013) provides detailed information on the distribution records of the species described from adult stage (Table 1).Zelinka, 1928(Bacescu 1961;Bacescu et al. 1971).Sergeeva (2003) reported the occurrence of several kinorhynch species from Crimean waters as well.
The previous reports of E. dujardinii from the Black Sea are by Bacescu et al. (1963Bacescu et al. ( , 1971)), Marinov (1964) and Bacescu (1968) although considered questionable (Higgins 1983) because of the lack of details or descriptions.Bacescu et al. (1971) mentioned that the habitat of the species was upper infralittoral rocky substrate, occupying a niche within the sediments mixed with diatoms and cyanophyceans that cover the rocky substrate as well as the muddy sands from the Danube mouth.
The known kinorhynch fauna of Turkey is scarce mainly due to just recently conducted surveys of meiofauna (Ürkmez et al. 2016) or the fact that only a few researchers around the world deal with these organisms.Moreover, meiobenthic sampling techniques generally result in obtaining just a few individuals; collecting the number of specimens needed for taxonomic research requires specific sampling procedures and locations targeting the members of this phylum (Pardos F. pers comm; Sørensen & Landers 2014).

Figure 2 .
Figure 2. Echinoderes dujardinii, adult male; introvert retracted, anterior end to the left.A, ventral view.Arrows mark the lateral terminal spines.Note the two first segments as cuticular closed rings and the remaining 9 segments with paired sternal plates.B, dorsal view.Cuticular thickenings, or pachycycli, reinforce the anterior edge of every segment (arrows).