Semiodera nishii, Salazar-Vallejo, 2012

Salazar-Vallejo, Sergio I., 2012, 3562, Zootaxa 3562, pp. 1-62 : 31-33

Semiodera nishii n. sp.

Figure 11

Type material. Northwestern Pacific Ocean. Japan. Holotype ( CMNH-550 ) and two paratypes ( CMNH-546 , 549 ), Ubarajima Island , Katsuura (35°08' N, 140°20' E), Boso Peninsula, 10–15 m, coral rocks, 30 Oct. 1997, E. Nishi, coll. (paratypes 14–17 mm long, 2.5–3.5 mm wide, cephalic cage 5–8 mm long, 41–65 chaetigers).

Additional material. South China Sea. One specimen ( SMF-15353 ), Chinese-German Expedition to Hainan Island, dive, Shalao , 12 m, 4 Apr. 1992, D. Fiege & R. Sun, coll. (17.5 mm long, 2.5 mm wide, cephalic cage 6.5 mm long, 55 chaetigers) .

Description. Holotype pale (CMNH-550), tapering posteriorly into cylindrical thin cauda ( Fig. 11A); 22.5 mm long, 3 mm wide, cephalic cage 8 mm long, 66 chaetigers. Tunic thin, without sediment, integument rugose, finely areolated; body papillae short, globose, arranged in 1–2 irregular transverse bands per segment in anterior and median chaetigers, each with numerous, similar sized papillae; posterior chaetigers with more numerous longer papillae, bottle-shaped.

Cephalic hood not exposed; anterior end observed in one paratype. Prostomium low cone, colorless, four black eyes, not coalescent. Caruncle poorly developed. Palps thick, longer than branchiae; palp keels rounded, low. Dorsal lip reduced, lateral and ventral lips fused, projected anteriorly.

Branchiae cirriform, sessile on branchial plate, arranged in a single continuous row, with four dorsal large filaments and 20 smaller filaments, arranged in two lateral loops ( Fig. 11D), each with 10 filaments, filaments decreasing in size inwardly. Nephridial lobes very thin, long, between the four dorsal larger branchiae and start of lateral loops.

Cephalic cage chaetae as long as 1/3 body length, or about three times longer than body width. Chaetigers 1–2 involved in cephalic cage; chaetiger 3 with chaetae longer than those present in following chaetigers, but not contributing to cage. Cephalic cage chaetae arranged in short ventrolateral rows; chaetiger 1 with 8–9 noto- and 7–8 neurochaetae, chaetiger 2 with 4–5 noto- and 5–7 neurochaetae per bundle.

Anterior dorsal margin of first chaetiger papillated, completely contracted lobe, number of papillae not determined. Anterior chaetigers with longer papillae, close to chaetal lobes. Chaetigers 1–3 increasing in length; chaetiger 3 longest, especially on its dorsal side. Sand cemented anterior shield dorsally extending to chaetiger 5 ( Fig. 11B), ventrally to chaetiger 4 ( Fig. 11C), reaching midventral line. Chaetal transition from cephalic cage to body chaetae gradual; chaetigers 3–7 with pseudocompound hooks, decreasing in size posteriorly ( Fig. 11E, F); falcate neurohooks from chaetiger 8. Gonopodial lobes in chaetiger 5, low transverse slits.

Parapodia poorly-developed, chaetae emerge from body wall ( Fig. 11G). Parapodia lateral, median neuropodia ventrolateral. Noto- and neuropodia as low lobes, with ovoid papillae in anterior and median chaetigers, posterior chaetigers with long bottle-shaped papillae.

Median notochaetae arranged in short rows, transverse to body axis; all notochaetae multiarticulate capillaries, about 1/5 as long as body width, 1–2 per fascicle, articles long, increasing in size distally. Neurochaetae multiarticulate capillaries in chaetigers 1–2; chaetigers 3–7 with 1–2 pseudocompound hooks. Falcate neurohooks from chaetiger 8, arranged in transverse rows, 2 per bundle in median chaetigers ( Fig. 11G), decreasing to 1–2 towards the posterior end. Each hook medially widened in median chaetigers, become thinner in posterior ones, with subdistal darker spot ( Fig. 11H).

Posterior end tapering to rounded lobe; pygidium with anus terminal, slightly projected, without anal cirri.

Etymology. This species is named after Eijiroh Nishi, a good friend and colleague, in recognition of his many publications on polychaetes, for his continued support of my research activities, and because he collected the specimens upon which this species is based.

Remarks. Semiodera nishii n. sp., belongs in a group defined by the presence of a poorly-developed dorsal shield, and two neurohooks in median chaetigers, which also includes S.salazarae n. sp. and S. treadwelli n. sp. However, S. nishii can be distinguished from the two other species, as it has neurohooks from chaetiger 8 (as opposed to chaetiger 9), and the lateral projections of the dorsal shield reach the midventral line, whereas in the two other species there is a midventral gap.

Distribution. Western Pacific Ocean, from Japan to the South China Sea, found boring in coral substrate in subtidal waters.