Orbiniella abyssalis, Blake, 2020

Blake, James A., 2020, New species and records of deep-water Orbiniidae (Annelida, Polychaeta) from the Eastern Pacific continental slope, abyssal Pacific Ocean, and the South China Sea, Zootaxa 4730 (1), pp. 1-61 : 38-40

Orbiniella abyssalis new species

Figures 18–19

urn:lsid:zoobank.org:act:204FB25A-7467-4248-B9D4-D14EC81414F3

Material examined. North Equatorial Pacific Ocean, abyssal plain, Clarion-Clipperton Fracture Zone, NOAA

BIE Project site, coll. D. T. Trueblood. Sta. DDT-05-93, veg. 20, 2– 5 cm fraction, 13 Aug 1993, 12°56.566′N, 128°35.408′W, 4870 m, holotype ( USNM 1594176 ) ; Sta. DDT-07-93, veg 24, 0–2 cm fraction, 02 Sep 1993, 12°56.303′N, 128°35.311′W, 4844 m, 1 specimen ( USNM 1594177 ) ; Sta. DDT-11-93, veg. 22, 0–2 cm fraction, 04 Sep 1993, 12°56.055′N, 128°35.695′W, 4859 m, paratype ( USNM 1594178 ) ; Sta. DDT-12-93, veg. 6, 0–2 cm fraction, 04 Sep 1993, 12°56.329′N, 128°35.698′W, 4851 m, paratype ( USNM 1594179 ) ; Sta. DDT-08-94, 29 Jul 1994, 12°55.020′N, 128°35.400′W, 4880 m, 1 specimen ( USNM 1594180 ) .

Description. Holotype elongate, of moderate size, mostly complete in two parts, 8.0 mm long, 0.7 mm wide for 65 setigers. Paratype (USNM 1594178) incomplete, 17 setigers, 1.35 mm long, 0.275 mm wide. All segments short, crowded, about eight times wider than long ( Fig. 18A ). Body with similar segments throughout, lacking a separate thorax and abdomen. Body dorsoventrally compressed, without dorsal or ventral longitudinal grooves. Parapodia all lateral, not shifted dorsally in posterior segments. Each segment separated from following by an intersegmental area formed of 2–3 narrow raised annulae. Color in alcohol: light tan.

Pre-setiger region short, narrower than anterior setigers, merging with setiger 1 ( Fig. 18A ). Prostomium short, broadly rounded anteriorly ( Fig. 18A ); eyespots absent; nuchal organs low mounds on sides of posterior prostomium ( Fig. 18A ). Peristomium a single large ring, longer than setiger 1, with one weakly defined lateral groove, not crossing dorsum or producing separate rings ( Fig. 18A ).

Setiger 1 and following segments separated from one another by intersegmental groove with narrow annular rings. Branchiae entirely absent. Noto- and neuropodia formed as elongate lobes, tapering to rounded apex ( Fig. 18B ). Notopodia with short, clavate postsetal lamellae ( Figs. 18B , 19A ); neuropodial postsetal lamellae absent. Notopodia with numerous long capillaries and 1–2 large, elongate acicular spines projecting well beyond parapodia ( Figs. 18C , 19 A–B); neuropodia with one large elongate acicular spine and numerous long capillaries; furcate setae absent. Spines thick, smooth, narrowing to pointed tip, some spines with slight curvature where narrowing begins ( Figs. 18C , 19B ). Capillaries not camerated, with minute bristles or barbs poorly developed; setae appearing smooth at 400x; bristles observed only at 1000x.

Pygidium not observed.

Methyl Green stain. No pattern, body stains uniformly, de-stains rapidly.

Remarks. Orbiniella abyssalis n. sp. is similar to three other deep-sea congeners: O. andeepia Narayanaswamy & Blake, 2005 , from Antarctica, O. petersenae Parapar, Moreira & Helgason, 2015 from the NE Atlantic, and O. tumida n. sp. from the California continental slope, in having a notopodial postsetal lamella and acicular spines in both noto- and neuropodia. Orbiniella abyssalis n. sp. differs from the other three species in having an unusually short and broad prostomium followed by a long, thick peristomium composed of a single ring, but with a weak lateral groove that does not cross the dorsum; the other species have two distinct peristomial rings. In addition, the noto- and neuropodial spines of O. abyssalis n. sp. are unusually long, about half as long as the capillaries. The spines of the other species are considerably shorter than the capillaries. The notopodial postsetal lamella is short and clavate in both O. abyssalis n. sp. and O. tumida n. sp. and longer and digitate in O. andeepia and O. petersenae . More details of these species and others are presented in Table 2 in the Discussion.

Etymology. The epithet is derived from the Latin abyssus, in reference to the deep-sea habitat of the species.

Distribution. Abyssal Pacific Ocean, 4844–4880 m.

Figures

FIGURE 18. Orbiniella abyssalis n. sp. Holotype (USNM 1594176): A, anterior end dorsal view, B, parapodium from an anterior setiger, anterior view; C, acicular spines.

FIGURE 19. Orbiniella abyssalis n. sp. Holotype (USNM 1594176): A, anterior setigers, in dorsal view showing notopodia with numerous capillaries and spines, and clavate notopodial lamella; B, posterior setigers in dorsal view showing notopodia with few capillaries and long spines.