Nephtys kersivalensis McIntosh 1908

Nephtys kersivalensis McIntosh, 1908

(Figure 8)

Nephtys kersivalensis McIntosh, 1908: 20, Pl. LXVI, Fig. 5; Rainer 1989: 882, Figs. 2A–F; Rainer 1991: 78, Fig. 2D; Hartmann- Schröder 1996: 229, Fig. 101; Dnestrovskaja & Jirkov 2001: 203; Laborda 2004: 406, Figs. 149A–C; Ravara et al. 2010: 55, Figs. 11, 21.

Material examined. Sea of Marmara: ESFM-POL/2013-1321, 06 June 2013, station Y1, 40°00’32’’N, 26°13’04’’E, 25 m, mud with black detritic material, 1 specimen; ESFM-POL/2013-1351, 07 June 2013, station Y5, 40°20’55’’N, 26°40’38’’E, 25 m, mud, 13 specimens; ESFM-POL/2013-1353, 07 June 2013, station Y5, 40°21’21’’N, 26°39’59’’E, 50 m, mud with Amphiura filiformis, 1 specimen; ESFM-POL/2013-1515, 08 June 2013, station Y9, 40°26’25’’N, 27°11’29’’E, 25 m, mud with Amphiura filiformis, 2 specimens; ESFM-POL/2013-1356, 16 June 2013, station Y22, 40°22’18’’N, 28°00’41’’E, 10 m, sand, 1 specimen; ESFM-POL/2013-1357, 19 June 2013, station Y39, 40°39’36’’N, 29°09’18’’E, 10 m, sandy mud with detritic material, 1 specimen.

Description. Largest specimen complete, 22.9 mm long, 1 mm wide, with 69 chaetigers. Colour cream or light brownish in ethanol. When pharynx not everted, prostomium subrectangular (0.2 mm long, 0.2 mm wide), anterior margin straight, posterior margin “U” shaped; when pharynx everted, prostomium becoming subpentagonal, with a “V” shaped posterior margin (Fig. 8A). Antennae (0.07 mm) and palps (0.09 mm) conical and similar in length, palps arising at ventro-lateral margin of prostomium (Fig. 8A). Pharynx with 10 pairs of bifid papillae (0.17 mm), separated by a dorsal and ventral gap; 22 rows of 4–6 long subterminal papillae (0.13 mm); middorsal papilla very long (0.4 mm), conical; midventral papilla absent, proximal part of pharynx smooth. Nuchal organs rounded, conspicuous. Two visible eyes only in small specimens. One pair of brownish jaws, triangular in shape, situated on the antero-lateral margin of pharynx (Fig. 8I).

Chaetiger 1 smaller than subsequent ones, directed anteriorly, parallel to prostomium; ventral cirri conical (0.07 mm) with a broad base, as long as antennae and palps. Parapodia biramous, “U” shaped in anterior region, “V” shaped in middle and posterior regions. Prechaetal lamellae well developed on chaetiger 2. Neuropodial and notopodial postchaetal lamellae well developed from chaetiger 3 and 4, respectively. In anterior parapodia (chaetiger 10), notopodial postchaetal lamellae rounded, 1/3 times longer than acicular lobe. Neuropodial postchaetal lamellae well developed, rounded with slightly angular corners, ½ times longer than acicular lobe; noto- and neuropodial prechaetal lamellae rounded, smaller than acicular lobes (Fig.8B). On middle parapodia (chaetiger20–40), notopodial postchaetal lamellae slightly truncated, longer than acicular lobe, neuropodial postchaetal lamellae rounded with slightly angular corners (see arrow at Fig. 8C), two times longer than acicular lobe; prechaetal lamellae bilobed; in notopodia, ventral parts slightly larger than dorsal parts in notopodia, and clearly unequal in neuropodia (Figs. 8C, D). In posterior parapodia (chaetiger 60), notopodial postchaetal lamellae rounded, similar size to acicular lobes, neuropodial postchaetal lamellae rounded, equal or slightly longer than acicular lobe; notopodial prechaetal lamellae bilobed with equal parts, neuropodial prechaetal lamellae unequally bilobed, both smaller than acicular lobes (Fig. 8E). Acicular lobes rounded (Fig. 8B) on anterior chaetigers, conical on middle and posterior chaetigers; with a rugose (zigzag-like structure) area (Fig. 8F) in the ventral surface of the acicular lobes, close to the acicula (difficult to see); clearly seen between chaetigers 8 and 20, indistinct/absent in subsequent chaetigers. Dorsal cirri small (0.08 mm), conical to digitiform. Ventral cirri conical in whole body, about as long as dorsal cirri.

Branchiae recurved, cirriform, with conspicuous papillae-like basal projection (similar in size to dorsal cirri on posterior chaetigers); present from chaetiger 4 to posterior end, except for last 5–6 chaetigers (Figs. 8B–E).

Three types of chaetae present in parapodia; capillary chaetae, barred chaetae and spinulated chaetae. Chaetiger 1 with 15–18 capillary chaetae (300 µm) arranged in a bundle in neuropodia, 6–7 barred (Fig. 8G) and 3–4 spinulated (Fig. 8H) chaetae with very smooth teeth in notopodia. Noto- and neuropodia of subsequent parapodia with up to 11 barred chaetae on preacicular position and up to 15–16 spinulated chaetae with one lateral row of spines on postacicular position. Barred chaetae thick in anterior chaetigers, thin in posterior chaetigers; bar occupying area diminishing towards posterior end; only a basal area of 0.1 mm lacking bars on chaetiger 10, while an area of 1.2 mm lacking bars on chaetiger 50.

One reddish-brown acicula present per ramus; with a straight tip in anterior region, with a strongly curved tip in middle and posterior regions. Pygidium rounded with one digitiform anal cirrus placed dorsally, as long as the last 3–4 chaetigers.

Remarks. Nephtys kersivalensis was originally described by McIntosh (1908) as a young stage of N. hombergii Savigny in Lamarck, 1818. Rainer (1989) provided detailed descriptions of these two closely related species. The Sea of Marmara specimens of N. kersivalensis (largest complete specimen 22.5 mm length with 74 chaetiger) are smaller than those found in the North Sea (39 mm length with 81 chaetiger) by Rainer (1989), in the coasts of Spain (40 mm with 90 chaetiger) by Laborda (2004), and in the southern Europe (up to 40 mm length with 69 chaetiger) by Ravara et al. (2010).

Distribution. North Atlantic Ocean (Rainer 1991; Laborda 2004; Ravara et al. 2010; Gil 2011); Mediterranean Sea (Coll et al. 2010), Sea of Marmara (present study).

Habitat. This species is typically found in muddy-sand bottoms. It occurs up to 295 m depth (Rainer 1991; Laborda 2004; Gil 2011). It was found at 10–50 m depths in the present study.