Erinaceusyllis defneae n. sp.

urn:lsid:zoobank.org:act: 8E647634-C084-4168-A003-103962BB7A13

Figures (4−6)

Erinaceusyllis belizensis; López, 1995: 253–257, fig. 37; Çinar, 1999: 140–142, fig. 4.47; San Martín, 2003: 230–233, fig. 122–123 (not Russell, 1989)

Material examined. Holotype. ESFM-POL/2022-017, station H2, 25.9.2022 . Paratypes. ESFM-POL/2022-015, 25.09.2022, station H2, 11 specimens (one specimen for SEM); ESFM-POL/2022-016, 25.09.2022, station H3, 4 specimens. Additional material examined. ESFM-POL/95-09, 05.07.1995, Çanakkale, 40.0492°N- 26.2161°E, on Zostera nolthii, 1 specimen .

Description. Holotype complete, minute, 0.90 mm long, 0.15 mm wide (at chaetiger 7), with 18 chaetigers. Complete paratypes 0.78–0.95 mm long, 0.16 mm wide, with 16–19 chaetigers.

Body pale yellow in colour without colour markings, tegument covered by small conical papillae and sand inclusions (Figs. 4A, B, 6A–C). Sand inclusions covered dorsum of some specimens so densely that it was impossible to distinguish papillae (Fig. 4A). Each segment with two-three rows of papillae. Dorsum of chaetiger 1–3 with small cylindrical papillae in two transverse rows; after chaetiger 3, dorsum of each segment with 4 small filiform papillae on anterior transverse row, 2 long digitiform papillae in mid-region and 4 small filiform papillae on posterior row (Fig. 4B). Papillae gradually increasing in length posteriorly.

Prostomium almost rectangular, wider than long, with 2 large eyes in a trapezoidal arrangement, setting close together on each side (Figs. 4A, B). One pair of large eyespots located on anterior margin of prostomium; with three antennae, similar in size, median antenna slightly larger, pear-shaped, with bulbous base and cylindrical tips; median antenna inserted between eyes, lateral antennae located near anterior margin, lateral to eyespots (Figs. 4, 6A–B). Palps small, shorter than prostomium, fused along their length.

Peristomium with two distinct tri-lobed flaps covering posterior part of prostomium including eyes; bearing a pair of tentacular cirri similar to antennae but slightly smaller (Figs. 4, 6A–B).

Dorsal cirri absent on chaetiger 2, morphologically similar to antennae and tentacular cirri, shorter than antennae and parapodial lobes in anterior parapodia, becoming elongate in mid-body parapodia (Fig. 4). Ventral cirri digitiform, shorter than parapodial lobes.

Parapodia conical, with cylindrical papillae on anterior face and distally on posterior face. Anterior parapodia with 6–7 heterogomph falcigers and solitary dorsal simple chaeta; all falcigers bidentate, blades of superior falcigers with coarsely serrated cutting edges (especially those near proximal part of blades), 32 µm long; those of inferior ones minutely serrated, 14 µm long; tips of proximal parts of falcigers coarsely serrated; dorsal simple chaeta starting from chaetiger 1, curved, slightly bifid, subdistally serrated (Fig. 5). Middle and posterior falcigers almost morphologically and numerically similar to anterior ones, but with larger blades; 40–18 µm long in middle parapodia and 35–18 µm long in posterior parapodia; superior falcigers in middle parapodia slightly curved (Figs. 5, 6D–F). Ventral simple chaeta present on last three chaetigers, slender, smooth, unidentate, with a pointed tip (Fig. 5C). Acicula solitary, acuminate (Fig. 5F).

Pharynx slender, almost 108 µm long, covering almost three or four segments; pharyngeal tooth large, triangular in shape, located at tip of pharynx opening; pharynx opening ciliated (SEM observation) (Figs. 4A, B; 6A, B). Proventricle barrel-shaped, 125 µm long, 85 µm wide, through 3–4 segments, with about 18 muscle cell rows (Fig. 4).

Pygidium small, with rounded papillae, anal cirri elongate, with a digitiform median papilla (Figs. 4, 6C).

Etymology. This species is named in honour of the little daughter of the first author, Defne Çinar.

Habitat. It occurs at 11–13 m depth on rocks with the algae Cystoseira crinita, Cladophora sp. and Phyllophora crispa .

Remarks. This species is similar to Erinaceusyllis belizensis (Russell, 1989), which was originally described from mangrove habitats in Belize (Caribbean Sea, west Atlantic) and has been reported from different parts of the world’s oceans (Atlantic and Pacific Oceans) including the Mediterranean Sea (Russell, 1989; López, 1995; Çinar, 1999; San Martín, 2003; 2005). Both species are minute and have characteristic peristomial flaps. However, E. defneae n. sp. from the Black Sea and Aegean Sea, differs from the Belizean species in the following characters: 1) the proventriculus of E. defneae n. sp. is larger (covering 3–4 segments) than that of E. belizensis (covering only 2 segments), 2) the number of muscle cell rows in the proventriculus of E. defneae n. sp. (18 rows) is higher than that of E. belizensis (15 rows), 3) the eyespots in the anterior edge of the prostomium of E. defneae n. sp. are larger than those of E. belizensis, 4) the dorsum of E. defneae n. sp. has a characteristic papillae rows, whereas that of E. belizensis has sparsely and irregularly distributed papillae, 5) the length of blades of superior falcigers in the mid-body (40 µm) of E. defneae n. sp. is much longer than that of E. belizensis (29 µm), 6) blades of all falcigers are clearly bidentate in E. defneae n. sp. vs. unidentate or provided by a subdistal spine in E. belizensis, and 7) the dorsal simple chaeta is subdistally serrated in E. defneae n. sp. vs. smooth in E. belizensis .

As specimens of E. defneae n. sp. are minute (smaller than 1 mm), it is hard to determine some morphological characters (e.g. serration on the dorsal simple chaeta) without SEM observation. However, the lengths of the proventriculus and the blade of the falcigers of E. defneae n. sp. clearly differ from those of E. belizensis . In the Mediterranean Sea, this species was reported in the western (López, 1995; Olano et al., 1998; San Martín, 2003) and the eastern (Çinar, 1999; Çinar & Ergen, 2002; Çinar, 2003; Musco, 2012; Çinar et al., 2014) Mediterranean Sea on a variety of habitats such as coralligenous walls and soft substrata. The descriptions of the specimens identified as E. belizensis from the Mediterranean Sea by López (1995), Çinar (1999) and San Martín (2003) coincides well with that of E. defneae n. sp., so the presence of E. belizensis in the region is highly questionable.