Orbiniella armata Blake 2021, new species

Orbiniella armata new species

Figures 51–52

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Orbiniella sp. 2: Blake et al. 1987: C-4; Hilbig 1994: 942 (in part).

Material examined. (5 specimens) Southeastern USA, U.S. South Atlantic ACSAR program, coll. J.A. Blake, Chief Scientist. Off Charleston, South Carolina, Sta. 16: Cruise SA-6, Rep. 2, Cruise SA-6, Rep. 2, 20 Nov 1985, 31°35.10′N, 75°10.34′W, 3009 m, holotype (USNM 1622553) and 1 paratype (USNM 1622554); Cruise SA-5, Rep. 2, 16 Sep 1985, 31°35.14′N, 75°10.28′W, 3000 m, 1 paratype (USNM 1622555); Rep. 3, 16 Sep 1985, 31°35.14′N, 75°10.28′W, 3011 m, 1 juvenile (USNM 1622556).— Off Cape Fear, North Carolina, Sta. 13: Cruise SA-6, Rep 3, 21 Nov 1985, 32°55.25′N, 75°50.08′W, 3006 m, 1 paratype (USNM 1622557).

Description. A small species, largest specimen an incomplete paratype (USNM 1622554) with 47 setigers, 5.45 mm long and 0.51 mm long; holotype (USNM 1622553) complete but with posterior end damaged, with 33 setigers, 4.0 mm long, 0.5 mm wide. Body elongate, more or less uniform in width throughout; body segments similar, lacking a separate thorax and abdomen. Individual segments short, about six times wider than long; lacking dorsal and ventral longitudinal grooves or ridges (Figs. 51 A–B, 52A). Individual segments with a single intersegmental ring in anterior setigers (Figs. 51 A–B, 52A), increasing to two or three narrow rings in middle and posterior setigers (Fig. 52B), producing tri- and quadriannulate segments. Color in alcohol: light tan to opaque white.

Pre-setiger region narrower than following segments, about as long as first 4–5 setigers (Figs 51 A–B, 52A). Prostomium wider than long, broadly rounded on anterior margin (Figs 51A, 52A); dorsal surface relatively smooth; eyespots absent; nuchal organs ciliated depressions on lateral margins. Peristomium with three rings (Figs. 51 A–B, 52A); dorsally with first ring narrow, second ring largest, and third ring narrow (Fig. 51A); ventrally with first ring expanded, surrounding mouth with five large lobes forming upper lip of mouth and numerous lobes along lower lip of mouth (Fig. 51B); middle and posterior rings narrower, relatively smooth (Fig. 51B). Proboscis not everted on any specimens.

Setiger 1 and following segments with relatively simple noto- and neuropodia formed of short tori from which spines and capillaries emerge (Figs, 51C, 52C). Single short, digitate postsetal lobe present in notopodia (Fig. 51A, C); absent in neuropodia.

Noto- and neuropodia typically with a single exceptionally large acicular spine and 4–8 long, serrated capillaries (Figs. 51C, 52C); spines may increase up to two or three per noto- or neuropodium in some middle and posterior setigers but inconsistent between specimens; individual spines unusually long, thick, tapering apically to a blunt tip (Fig. 52D). Capillaries not camerated, each with minute, sharply pointed barbs along length.

Pygidium damaged, narrow, cirri not observed on types. One juvenile with three thin cirri.

Remarks. Orbiniella armata n. sp. from lower slope and abyssal depths off the Southeastern USA is most similar morphologically to O. abyssalis Blake, 2020 from the abyssal plain of the north equatorial Pacific Ocean in having similarly shaped large elongate noto- and neuropodial spines along the body. The main difference between the two species, however, is that the peristomium of O. armata n. sp. is formed of three separate rings, whereas that of O. abyssalis consists of only a single smooth ring.

Etymology. The epithet is from armatura, Latin for a weapon or an item used to defend. In this instance the armature are the unusually large projecting spines present in the noto- and neuropodia of this species.

Distribution. Off South Carolina, lower continental slope or abyssal depths, 3000–3011 m.