Leitoscoloplos pustulus Blake 2021, new species

Leitoscoloplos pustulus new species

Figures 8–9

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Leitoscoloplos nr. acutus: Hilbig 1994: 942. Not Verrill 1873.

Material examined. (289 specimens) Southeastern USA, off Cape Hatteras, North Carolina, US South Atlantic ACSAR program, coll. J.A. Blake, Chief Scientist. Sta. 9: Cruise SA-3, R/ V Gyre, Rep. 1, 22 Jul 1984, 35°28.30′N, 74°47.70′W, 579 m, holotype (USNM 1620901), 60 paratypes (USNM 1620902); Rep. 2, 22 Jul 1984, 35°28.40′N, 74°47.50′W, 614 m, 43 paratypes (USNM 1620903); Rep. 3, 22 Jul 1984, 35°28.30′N, 74°47.60′W, 598 m, 28 paratypes (USNM 1620904). Cruise SA-4, R/V Cape Hatteras, Rep. 1, 24 May 1985, 35°28.41′N, 74°47.44′W, 640 m (20, USNM 1620905); Rep. 2, 24 May 1985, 35°28.41′N, 74°47.56′W, 603 m (35, USNM 1620906); Rep. 3, 24 May 1985, 35°28.28′N, 74°47.52′W, 623 m (26, USNM 1620907). Cruise SA-5, R/ V Gyre, Rep. 1, 25 Sep 1985, 35°28.41′N, 74°47.46′W, 629 m (~30, USNM 1620908); Rep. 2, 25 Sep 1985, 35°28.41′N, 74°47.47′W, 629 m (32, USNM 1620909); Rep. 3, 25 Sep 1985, 35°28.27′N, 74°47.61′W, 629 m (14, USNM 1620910).

Description. Holotype complete, with 105 setigers, 13.2 mm long, 0.7 mm wide across middle of thoracic region. Body elongate, with thoracic region narrow at first, becoming wider and dorsoventrally flattened in middle and posterior segments, with individual segments short and wide, about 4–6 times wider than long near transition to abdominal segments. Individual thoracic segments separated by narrow transverse groove from about setiger 6, becoming more distinct and broader from about setiger 10 (Fig. 8A). Abdominal segments short and wide at first, becoming even shorter and crowded posteriorly. Abdominal segments with a biannulate appearance and an expand- ed intersegmental area posterior to elevated parapodia. Middle and posterior abdominal segments short, crowded, about twice as wide as long. Shallow mid-ventral groove present from anterior segments to near posterior end. Color in alcohol light tan.

Pre-setiger region triangular, short, about as long as setiger 1 and part of setiger 2 (Figs. 8 A–B, 9B). Prostomium triangular, narrowing to pointed apex (Figs. 8 A–B, 9B); nuchal organs narrow curved slits on posterior lateral margin (Fig. 9B), observed with difficulty; eyespots absent. Peristomium a single short smooth achaetous ring dorsally and laterally (Fig. 8A); ventrally forming upper and lower lips of mouth (Fig. 8B). Mouth surrounded by several thickened lobes (Fig. 8B); proboscis when everted with no more than three lobes.

Thorax of holotype and larger paratypes typically with 14 setigers, rarely 15, with abrupt transition to abdominal segments (Figs. 8A, 9A). Boundary between thorax and abdomen indicated by elongation of neuropodia and decrease in number of neurosetae. Thoracic notopodial lobes arising from narrow base, triangular in shape, narrowing apically (Fig. 8C); neuropodia digitiform, shorter than notopodial lobe, arising from broadly rounded base surrounding neuropodial lobe (Fig. 8C); entire neuropodium recessed into a notch on body wall. Abdominal notopodia elongate, narrow, digitiform, tapering to narrow rounded tip (Fig. 8D), becoming narrower in posterior setigers (Fig. 8E). Short, rounded interramal protuberance or process present between noto- and neuropodial bases, best observed on anterior abdominal parapodia (Fig. 8D) but also present in middle abdominal segments, albeit observed with difficulty. Abdominal neuropodia thickened, relatively short in middle and posterior segments, each divided into two apical lobes, with dorsal lobe longest (Fig. 8 D–E); each neuropodium with elongate, bulbous, fleshy subterminal flange (Fig. 8D); flange often with distinct large blister-like rounded protuberance on lateral or posterior margins, best developed in middle abdominal segments (Figs. 8E, 9C, arrows). Many specimens with large hole or opening on flange, suggesting the protuberance had erupted. Contents of blisters variable, appearing glandular rather than reproductive in nature. Neuropodium of setiger 14 on holotype with extra rounded lobe below setae; this becoming larger and transitioning to subpodial flange on abdominal setigers 15 – 16. Otherwise, no extra subpodial papillae or stomach papillae observed along body of any specimens.

Branchiae typically from setiger 11–12, usually 12 (holotype); initial thoracic branchiae small, becoming full size by about setigers 13–15 (Fig. 8A). All branchiae relatively short; anterior branchiae triangular, tapering to narrow papillate rounded apex (Fig. 8D); branchiae of middle and posterior abdominal segments generally thicker, tapering to wider rounded apex (Fig. 8E); each branchia with transverse folds and cilia on inner and lateral margins (Fig. 8 D–E).

Notosetae camerated capillaries and furcate setae; about 30 capillaries in two rows in thoracic notopodia reduced to 10–15 long, thin camerated capillaries in abdominal segments accompanied by 0–2 furcate setae. Thoracic neurosetae all capillaries with about 60 setae in three rows; abdominal neurosetae include 2–7 capillaries with few barbs along one edge (Fig. 8E inset) and 1–2 short protruding aciculae, these minute, with pointed tip (Fig. 8D inset). Furcate setae of abdominal notopodia with unequal tynes, each tyne with a rounded and notched apex within which an opening and narrow channel extending into the tyne can be observed with light microscope; narrow elongate fibrils present between tynes (Fig. 8F); flail setae absent.

Pygidium a rounded lobe surrounding anal opening surmounted by two lobes from which two long, thin anal cirri arise (Fig. 9D).

Variability. The most unusual features of Leitoscoloplos pustulus n. sp. are the rounded, blister-like swellings on the neuropodial subpodial flanges of abdominal segments. These are typically present on all of the large specimens and may be limited to a few segments or prominent in one form or another along most of the abdominal region. Small swellings are usually clear or filled with large cells; large swellings are dark and appear to be filled with granular material, possibly ingested sediment that has somehow entered the subpodial flanges from the intestinal tract. There is no evidence that the flanges are modified for gamete storage and release or as brood chambers. A large number of the flanges were observed to be open and empty suggesting the contents had been discharged.

An extra thoracic neuropodial lobe or papilla was observed on the last thoracic setiger in most specimens examined. Over the next two abdominal segments, this lobe or papilla is transformed into the subpodial flange of the neuropodia. There are no other extra lobes or papillae evident along the body.

Remarks. Specimens of Leitoscoloplos pustulus n. sp. from off Cape Hatteras were originally identified as L. cf. acutus, a widely reported species in nearshore shelf depths along the Atlantic coast of the U.S. and Canada (see above). Leitoscoloplos pustulus n. sp., however, differs from L. acutus in having instead of lacking an interramal process between the abdominal noto- and neuropodia, having an inflated subpodial flange often with a prominent rounded blister or swelling instead of smooth, narrow flanges without swellings, and in having, instead of lacking, an extra neuropodial lobe on the last thoracic setiger that clearly transitions into the abdominal subpodial flange over subsequent abdominal neuropodia.

Biology. Eggs were observed on several paratypes. These ranged from 40–100 µm in diameter. Unusually dense assemblages of benthic infaunal invertebrates occurred in the continental slope sediments off Cape Hatteras, North Carolina, at Station 9 at 600 m where L. pustulus n. sp. was discovered (Blake & Hilbig 1994). Infaunal densities ranged from 24,055 to 61,244 (mean = 46,255) individuals per m 2 in nine samples taken at Station 9 in 1984 and 1985.

High sedimentation rates and organic carbon flux have been recorded from the slope off Cape Hatteras and may account for the high infaunal productivity in the area. Most of the dominant infaunal organisms are species more typical of coastal habitats rather than deep-sea species that dominate other areas of the U.S. Atlantic continental slope. A parallel investigation regarding the nature of organic matter in the Cape Hatteras sediments revealed a mixture of both marine and terrestrially derived carbon (Rhoads & Hecker 1994).

Etymology. The epithet is from the Latin, pustula for bubble or blister, referring to the nature of the abdominal subpodial flanges which often bear a blister-like swelling on the lateral or posterior margin.

Distribution. Off Cape Hatteras, North Carolina, 579– 640 m.