Orbiniella longilobata new species

Figure 22

urn:lsid:zoobank.org:act: 02448FFD-904C-4659-BE6C-B73F1A376216

Material examined. South China Sea, off Brunei, Island of Borneo, Site CA2, R / V Emma, coll. P.A. Neubert, box corer, Sta. TA7 , 2 Jul 2011, 5°25.805′N, 113°22.188′E, 2004 m, holotype (MCZ 153588); Sta. SE5 , 28 Jun 2011, 5°35.739′N, 113°47.115′E, 1947 m, 1 paratype (MCZ 153589); Sta. TA5 , 2 Jul 2011 5°27.844′N, 113°26.572′E 2008 m, 1 specimen (UBD).— Site CA1, R / V Emma, coll. J.A. Blake, box corer, Sta. 49, 2 Jun 2011, 5°44.405′N, 114°13.993′E, 1199 m, 1 paratype (MCZ 153590) .

Description. A small species, all specimens incomplete. Holotype with 18 setigers, 2.14 mm long, 0.18 mm across pre-setiger region, 0.43 mm across setiger 6; paratype (MCZ 153590) with 17 setigers, 2.01 mm long, 0.4 mm across anterior setigers. Body dorsoventrally flattened, with narrow segments, up to eight times wider than long (Fig. 22 A–B); without dorsal or ventral longitudinal grooves. All parapodia lateral, not shifted dorsally. Anteriormost setigers with narrow intersegmental groove, best developed ventrally (Fig. 22 A–B). Color in alcohol: light tan.

Pre-setiger region about 2.5 times narrower than following segments, about as long as first three setigers (Fig. 22A). Prostomium conical, rounded on anterior margin; eyespots absent; nuchal organs prominent lateral ciliated lobes (Fig. 22A). Peristomium with two narrow annular rings distinctly separated from one another dorsally and ventrally by inter-annular grooves; when swollen, grooves providing a superficial appearance of four annular rings (Fig. 22 A–B). First annular ring forming posterior lip of mouth; anterior lip of mouth with three lobes (Fig. 22B).

Setiger 1 and 2–3 following segments separated from one another by swollen intersegmental grooves (Fig. 22 A–B). Branchiae entirely absent. Noto- and neuropodia weakly developed, elongate, more or less conical. Notopodia with long, digitate postsetal lamella (Fig. 22C), narrowest and longest in posterior setigers. Setae include capillaries and 1–2 acicular spines in both noto- and neuropodia (Fig. 22C); furcate setae absent. Capillaries with a row of barbs along one edge. Spines thick, smooth, tapering to narrow tip (Fig. 22 D–E); some posterior spines long, extending well beyond parapodia.

Pygidium not observed.

Methyl Green stain. No pattern, body stains uniformly.

Remarks. Orbiniella longilobata n. sp. belongs to a group of species having a notopodial postsetal lobe instead of lacking one. In O. longilobata n. sp., the notopodial postsetal lobe is long, narrow and digitiform instead of short and thick as in most species. This species is also characterized by having a narrow pre-setiger region with two peristomial rings and two wide inter-annular rings that superficially provide the peristomium with the appearance of four annular rings. The long acicular spines that occur in some posterior parapodia of O. longilobata n. sp. are similar to those of O. abyssalis n. sp. However, in the latter species, the peristomium consists of a single large ring with weakly developed lateral grooves instead of two prominent peristomial rings as in O. longilobata n. sp.

Etymology. The epithet, longilobata is from the Latin, longus, for long and lobus for lobe in reference to the elongate, dorsal postsetal lobes that are characteristic for this species.

Distribution. South China Sea, off Brunei, Island of Borneo, 1199–2008 m.