Scoloplos papillatus Blake 2021, new species

Scoloplos papillatus new species

Figures 15–17

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Material examined. (36 specimens) Southeastern USA, off Cape Hatteras, North Carolina, MMS Cape Hatteras Survey, coll. J.A. Blake, Chief Scientist, R / V Endeavor. Sta. CH-3: Aug 1992, 35°37.08′N, 74°46.12′W, 812 m, holotype (USNM 1621017) and 17 paratypes (USNM 1621018). Sta. SA-9: Sep. 1992, 35°28.36′N, 74°41.26′W, 620 m, 18 paratypes (USNM 1621019).

Description. A large, elongate species; thoracic segments dorsoventrally flattened, often with middle thoracic segments swollen dorsally, likely from location of internal retracted pharynx; abdominal segments ventrally round- ed, dorsally flattened with elevated parapodia. Shallow ventral groove present along entire body on most specimens; dorsal grooves and ridges absent. Holotype complete, coiled, with 182 setigers, 45 mm long, 1.8 mm across thorax; with 17 thoracic setigers and branchiae from setiger 14 (Fig. 17A). Large incomplete paratype (USNM 1621018), with 180 setigers, 37 mm long, 2.1 mm wide across thorax; with 18 thoracic setigers and branchiae from setiger 14 (Fig. 17B). Transition from thorax to abdomen abrupt, denoted by appearance of elongate and enlarged neuropodia, simple at first, becoming longer and with apex split over successive segments. Thoracic segments short, about five times wider than long. Color in alcohol light tan; dorsum of abdominal segments between branchiae with 1–3 medial dorsal brown pigment spots in intersegmental swelling (Fig. 17D arrows), this distinctive pigment conspicu- ous on large specimens; large subpodial flanges of middle and posterior abdominal neuropodia often with darkly pigmented internal glands.

Pre-setiger region relatively short, slightly wider than long, triangular, overall as long as first two setigers (Fig.15A). Prostomium conical, tapering to pointed tip; nuchal organs vertical curved slits on posterior lateral margin; eyespots absent. Peristomium slightly longer than first setiger, with a single smooth annular ring dorsally (Fig. 15A), surrounding mouth ventrally, forming upper and lower lips; upper lip in two parts each with numerous narrow lobes (Fig. 15 B–C); lower lip with an equivalent number of narrow lobes.

Anterior thoracic notopodia with digitiform postsetal lobe, short at first (Fig. 15D), then becoming longer, narrow in posterior thoracic segments (Fig. 15E); each notopodial lobe arising from a thick base. Thoracic neuropodia initially with a shorter, thick postsetal lobe arising from a broadly rounded base (Fig. 15D); posterior thoracic neuropodia developing short postsetal lobe and a short subpodial papilla ventral to neuropodium (Fig. 15E). Transition to abdominal segments abrupt, with fewer noto- and neurosetae. Abdominal notopodial postsetal lobes becoming narrow and elongate along rest of body (Fig. 16 A–C); abdominal neuropodia narrow, divided apically into two parts separated by notch; medial lobe long, pointed; ventral lobe shorter, rounded apically, directed laterally, appearing as ventral cirrus (Fig. 16 A–C). Interramal cirrus absent. Each abdominal neuropodium with narrow subpodial flange (Figs. 16 B–C, 17E); with one subpodial papilla on anterior abdominal segments (Figs. 16A, 17C). Subpodial flanges of middle and posterior abdominal setigers with numerous internal glands; these darkly pigmented on many specimens (Fig. 16C).

Branchiae from posterior thoracic setiger 13 or 14 (Fig. 15A); branchia short, narrow at first, becoming leaflike, longer, and full size by first abdominal segment; each anterior branchiae broad, tapering to narrow papillate tip (Fig. 16A); a few anterior abdominal branchiae bifid, with a second apical papilla (Fig. 16A inset). Branchiae of middle and posterior setigers becoming longer, triangulate, rarely asymmetrical (Fig. 16 B–C). Each branchia ciliated along lateral and medial margins.

Thoracic notosetae numerous thick, long, camerated capillaries arranged in 4–5 rows. Thoracic neurosetae arranged in about five rows with similar appearing camerated capillaries and 5–10 uncini alternating with capillaries in second row; uncini occurring over first 7–10 setigers, becoming reduced to 3–4 uncini in lower part of setal fascicle; then either absent or not observed in later thoracic setigers. Individual uncini with shafts smooth on convex side, tapering to narrow, rounded tip; concave side of shaft flattened, bearing paired transverse knobs or barbs along most of shaft (Fig. 15 F–G). Abdominal notosetae thin, camerated capillaries and 1–2 furcate setae. Furcate setae with unequal tynes, each tyne with blunted tip and apical notch; shaft with rows of transverse barbs or ridges; tynes with a row of thin needles extending medially (Figs. 15H, 17G). Abdominal neurosetae with up to 4–5 thin capillaries, each with short barbs along one edge and 1–2 curved aciculae, sometimes protruding, with rounded tip (Fig. 16A insets). Flail setae not observed.

Pygidium short, with about ten narrow dorsal lobes, two large lateral lobes, and a single large ventral lobe surrounding anal opening; with two short dorsal anal cirri arising dorsally (Figs. 16D, 17F).

Remarks. Among species of Scoloplos along the U.S. Atlantic coast having a reduced number of uncini in thoracic neuropodia, S. papillatus n. sp. from upper slope depths is most similar to S. verrilli n. sp., (see below) a common species in New England near-shore shelf sediments. The two species are similar in size (up to 42–45 mm long) and number of setigers (about 180–200). S. papillatus n. sp. has 17–18 thoracic setigers whereas S. verrilli n. sp. has 16–17 thoracic setigers; both species have branchiae from setigers 13–14. Obvious differences are in the development of extra podial lobes in posterior thoracic setigers: S. papillatus n. sp. develops both a subpodial lobe and subpodial papillae ventral to the neuropodium, whereas S. verrilli n. sp. develops a second postsetal lobe on the neuropodium and a subpodial lobe. There also appear to be differences in the nature of the upper lip of the mouth: in S. papillatus n. sp., the upper lip is divided into two parts, each of which has numerous narrow lobes; in S. verrilli n. sp., the upper lobe is formed into two large, relatively smooth lobes that do not appear to be further divided. The most conspicuous difference between the two species, however, is that S. papillatus n. sp. has 1–3 medial brown pigment spots in dorsal intersegmental swelling in abdominal segments, whereas in S. verrilli n. sp. the intersegmental areas are neither swollen nor pigmented.

Scoloplos papillatus n. sp. is also similar to S. californiensis Blake, 2020 from deep water off California and S. sparsaciculus Blake, 2020 from deep water in the South China Sea in having a reduced number of uncini in the thoracic neuropodia. Both of the two latter species have an extra subpodial lobe, but this is only present in anterior abdominal segments, whereas S. papillatus n. sp. also has an extra subpodial lobe on posterior thoracic setigers. S. papillatus n. sp. has 17–18 thoracic setigers and branchiae from setigers 13–14, whereas S. californiensis has 12 thoracic setigers and branchiae from setigers 11–12.

Biology. The upper continental slope off Cape Hatteras, North Carolina, where Scoloplos papillatus n. sp. was discovered is unusual in having high infaunal densities of 24,055 to 61,244 (mean = 46,255) individuals per m 2 (Blake & Hilbig 1994). The fauna is dominated by polychaetes such as Scalibregma inflatum Rathke, 1843, Cossura longocirrata Webster & Benedict, 1887, and Aricidea quadrilobata Webster & Benedict, 1887, species that are more typical of shelf depths. Rhoads & Hecker (1994) found that organic matter in the Cape Hatteras sediments is a mixture of both marine and terrestrially derived carbon that is more typical of continental shelf sediments, suggesting that the high percentage of refractory organic matter favors the survival of preadapted shelf species over those from adjacent slope environments.

Etymology. Latin, for papilla, a nipple or bud, referring to the subpodial papillae that occur on upper and lower margins of the subpodial flanges of this species.

Distribution. Off Cape Hatteras, North Carolina, upper continental slope, 620– 812 m.