Chaetocirratulus sandersi Blake 2022, new species

Chaetocirratulus sandersi new species

Figures 10–11

urn:lsid:zoobank.org:act: B641B107-211D-4486-8C92-8A6710D46B48

Chaetozone sp. B: Maciolek et al. 1987a: D-2 (in part).

Material examined. Off New Jersey and Delaware, U.S. Mid-Atlantic ACSAR Program, coll. R. Petrecca, Chief Scientist. Sta. 2A: Cruise Mid-1, Leg 1, R/ V Cape Hatteras, 01 Apr 1984, 38°35.78ʹN, 72°53.656ʹW, 2013 m, holotype (USNM 1660938).

Description. A moderately large species, holotype complete but damaged, 18 mm long, 3.5 mm wide across anterior setigers, with ca. 80 setigers; middle body segments about 4.5 mm wide, then narrowing to posterior end. Specimen partially damaged between setigers 19–20, distorting overall shape, but both sections remain joined (Fig. 11A). Body fusiform, widest in middle segments, with narrow crowded segments (Figs. 10A–B, 11A). Parapodia lateral with dorsal and ventral surfaces broad, with distinct intersegmental grooves across both surfaces (Fig. 10A– B). Dorsum elevated with distinct mid-dorsal groove (Fig. 10A), deepest along anterior segments, less prominent in middle and posterior segments; venter also elevated, but not as high, also with mid-ventral groove along anterior segments, with narrow ridge in groove (Fig. 10B). Middle and posterior segments lacking ventral groove. Color in alcohol light tan; venter of peristomium with a few minute scattered pigment spots.

Pre-setiger region broadly triangular, wider than long, about as long as first five setigers (Figs. 10A–B, 11A). Prostomium short, wedge-shaped, narrowing to rounded anterior margin (Fig. 10A–D); eyespots absent; nuchal organs narrow slits at posterior lateral margins. Peristomium with two rings, first largest with several transverse grooves or slits; dorsally surrounding posterior prostomium (Fig. 10A, C); ventrally forming large lip around mouth (Fig. 10 B, D); second ring narrower, dorsally bearing a pair of dorsal tentacles and first branchiae lateral to tentacles (Fig. 10A, C). Subsequent branchiae on setigers dorsal to notosetae. Most branchiae missing; a few short narrow filamentous branchiae retained in middle segments.

Parapodia well-developed along entire body, with those of first 20 anterior setigers largest and most prominent (Fig. 10A–C); noto- and neuropodia distinct ridges from which setae arise; separate postsetal lamellae not present. Setae include long, smooth capillaries and acicular spines. Capillaries numbering 9–10 per noto- and neuropodia in anterior setigers, reduced to 5–6 in middle segments and 1–3 in posterior setigers. Some capillaries with thicker shafts transitioning to acicular spines in mid-body at about setigers 27 (neuropodia) and 31 (notopodia). Individual spines with straight, not sigmoid, shafts and narrow rounded tips (Fig. 11C–D). Spines 1–2 per notopodium and 2–3 per neuropodium, accompanied by 1–3 capillaries.

Pygidium with a simple rounded, terminal lobe ventral to anal opening (Fig. 11B).

Methyl green staining. Methyl green stains the pre-setiger region heavily on both sides (Fig. 10C–D), continuing on the parapodia and producing transverse bands across the venter of anterior setigers (Fig. 10D); dorsal tentacles and branchiae not staining.

Remarks. Among four species of Chaetocirratulus reported in this study from the U.S. Atlantic continental slope, C. sandersi n. sp. is the only one to have two peristomial rings instead of three. These are complete both dorsally and ventrally. No body pigment is present and there are distinct mid-dorsal and ventral grooves, the latter of which has a medial ridge. The morphology of the four species is compared in Table 2.

Etymology. This species is named for the late Dr. Howard Sanders, prominent ecologist whose classic studies with the late Dr. Robert Hessler on the North Atlantic deep-sea benthos introduced us to the undiscovered richness of deep-sea benthic infauna.

Distribution. Off New Jersey and Delaware, continental slope, 2013 m.