Pseudoscalibregma palmeri Blake, 2015, new species

Pseudoscalibregma palmeri new species

Figures 6 A‒E; 7

Material examined. East Antarctic Peninsula, RVIB Nathaniel B. Palmer Cruise 2000-03, Collector, J.A. Blake.— Prince Gustav Channel, Sta. NBP-01, 768 m, 1 paratype (LACM Poly 7008).— Weddell Sea, Off Lindenberg Island, Sta. NBP-03, 385 m, holotype (LACM-AHF Poly 7009).

Description. Holotype incomplete, 6.2 mm long, 1.5 mm wide for 21 setigerous segments; paratype incomplete, 3.2 mm long, 1.2 mm wide with 16 setigerous segments. Body with weakly expanded thoracic region, narrowing posteriorly. Color in alcohol light tan, with reddish pigmented glands dorsally on setigers 3‒4 and ventrally on setigers 3‒6 (Figs. 6 A‒B); anterior and middle segments with small reddish pigment spots along individual annulae (Figs. 7 A‒B). Body segments with transverse rows of pads; setigers 1‒2 biannulate with large, prominent pads dorsally, not evident ventrally; subsequent setigers quadriannulate with numerous small pads closely spaced, becoming triannulate from about setiger 16. Venter with prominent ventral groove bearing large elevated pads from setiger 2, continuing posteriorly forming ventral ridge line with rounded, elevated pad at midpoint of each segment within groove (Figs. 6 B, 7B). Branchiae absent; pygidium not present on either specimen.

Prostomium with two long, diverging lateral horns directed anterolaterally (Figs. 6 A‒B); eyes absent, nuchal organs not observed; proboscis not everted. Peristomium a single lobed ring around prostomium dorsally (Fig. 6 A), ventrally forming upper and lower lips of mouth; upper lip with 9‒10 narrow lobes; lower lip with about seven large, elongate inflated lobes (Fig. 6 B).

Parapodia with elongate conical podial lobes throughout Fig. 7 B–C). Dorsal and ventral cirri from setiger 14, these short, inconspicuous at first, becoming longer and more prominent posteriorly (Fig. 7 C); dorsal cirri triangular, broad basally, tapering to pointed tip (Figs. 7 C‒D); ventral cirri asymmetrical with broad basal attachment and elongated, rounded tip (Figs. 7 C, E); both dorsal and ventral cirri with prominent darkly pigmented internal glands; glands on dorsal cirri exiting toward apex and glands on ventral cirri exiting along ventral surface (Fig. 7 D–E). Interramal papillae present between noto- and neuropodia, more developed in posterior parapodia (Figs. 6 C, 7C); these papillae with glandular contents, not ciliated (Fig 6 C).

Noto- and neuropodial capillary setae in 2‒4 rows throughout, successive rows with longer setae. Setigers 1‒2 with anterior group of 3–4 short, blunt-tipped spinous setae (Fig. 6 D); these homologous to lyrate setae that begin from setiger 3 and continue on subsequent segments. Lyrate setae, short, anterior to capillaries with unequal tynes bearing short bristles (Fig. 6 E); lyrate setae numbering 3‒4 per noto- and neuropodium in anterior segments and 9‒10 in posterior most segments.

Remarks. Pseudoscalibregma palmeri n. sp. resembles P. usarpium Blake, 1981 in the shape of the prostomium, single lobate peristomial ring, and by having prominent rows of annulated pads on anterior setigers. Major differences are that in P. usarpium the first two segments are quadriannulate, with subsequent segments having five annulae and with all annulae being large and prominent (Blake 1981). In contrast, in P. palmeri n. sp. the annulae of setigers 1‒2 are biannulate, with large, prominent pads, followed by quadriannulate segments where the rows are narrow and have numerous small inconspicuous pads bearing pigment spots.

The asymmetrical form of the ventral cirri in Pseudoscalibregma palmeri n. sp. is unique for the genus. The pigmented glands of the dorsal and ventral cirri are similar to those described for Scalibregma australis n. sp. earlier in this paper. Similar glands in the dorsal and ventral cirri of the closely related P. usarpium were reported by Blake (1981) but not described in detail. It is likely that these glands are widespread in scalibregmatids but have been largely overlooked. Similarly, the dorsal and ventral glands that occur in some anterior setigers from setiger 4 are similar to those of Scalibregma species but are newly reported for Pseudoscalibregma. The extensive array of pigment spots across the annulae in P. p al m e r i n. sp., however, is unique and has not been reported for other scalibregmatids.

The short anterior spinous setae of setigers 1‒2 present in P. pa l m er i n. sp. were not reported for P. usarpium. However, an examination of the holotype (USNM 60583) showed that such setae are present, but not as short as in P. palmeri n. sp.

Etymology. This species is named for the RVIB Nathaniel B. Palmer, research vessel of the United States Antarctic Program, on which most of the specimens reported in this paper were collected. Additionally, this research vessel was in turn named for Nathaniel B. Palmer, an American whaler, who is reputed to be among the first to sight the Antarctic continent.

Distribution. Known only from the vicinity of the Larsen Ice Shelf A area of the Weddell Sea side of the Antarctic Peninsula, 385‒ 768 m.