Chaetocirratulus furvus Blake 2018, new species

Chaetocirratulus furvus new species

Figures 33–34

Material examined. Off Peru, South of Callao, SEPBOP, R / V Anton Bruun Cr. 17, Sta. 660-G, coll. 22 Jun 1966, 12°58ʹS, 77°16ʹW, dredged, 1000 m, holotype (USNM 1490735) and 1 paratype (USNM 1490736).

Description. Collection includes holotype, one paratype, and several mid-body fragments. Holotype a large male with sperm platelets, complete but in three pieces, 60 mm long, 2.0– 2.2 mm wide, with 106 setigerous segments; paratype an anterior fragment with 32 setigers. Body generally cylindrical in cross section with venter weakly flattened; dorsal groove absent, weakly developed mid-ventral groove present in middle body segments. Posteriormost 15 segments expanded laterally, rounded dorsally, and flattened ventrally (Figs. 33B, 34C). Individual segments well defined with distinct segmental grooves. Color in alcohol tan, with prominent black pigment on parapodia, scattered on dorsum of anterior-most segments (Fig. 34A) and across venter of anterior setigers. Pigment strongest on venter of holotype posterior to mouth (Fig. 34B), then continuing over next 18 setigers as bands on posterior margin of individual segments; similar pigment continuing as black spots posterior to notosetae for about 20 segments; far posterior segments not pigmented (Fig. 34C); similar pigment on paratype except not as dark.

Pre-setigerous region relatively short, bulky, slightly longer than wide, broadly rounded anteriorly, bearing short, triangular prostomium narrowing to rounded tip (Figs. 33A, 34 A–B); eyespots absent; nuchal organs narrow grooves at posterior lateral margins. Peristomium dorsally elevated but not as a separate crest, with four weakly developed annular rings, denoted by three thin grooves as lines across dorsum (Fig. 33A); ventrally, first two peristomial rings forming lower lip of mouth (Fig. 34B). Dorsal tentacles arising from posterior margin of peristomium (Fig. 33A); first pair of branchiae arising lateral to dorsal tentacles also on posterior margin of peristomium (Fig. 33A). Second pair of branchiae on setiger 1 dorsal to notosetae (Fig. 33A).

Parapodia of anterior setigers well developed, forming rounded shoulders along lateral margins (Fig. 33A). Noto- and neuropodia of first 15–20 segments with 12–16 capillaries arranged in two rows with those of second row thicker than those of first. Setae reduced to three thick and three thin capillary setae by setiger 30; thick capillaries of neuropodia transitioning to three blunt tipped spines accompanied by 1–2 thin capillaries by setigers 30–37; two spines first present in notopodia from setigers 35–37. Spines and capillaries continuing along body to posterior end, typically with two spines and 1–2 capillaries in notopodia and 2–3 spines and 1–2 capillaries in neuropodia; parapodia not elevated, setae not forming cinctures. Spines relatively inconspicuous along body, golden in color, straight to weakly sigmoid, tapering to narrow blunted tip (Fig. 33C).

Expanded posterior end terminating in pygidium with a few papillae dorsal to anal opening and rounded ventral lobe below anal opening (Figs. 33B, 34C).

Methyl Green stain. Entire pre-setigerous region retaining stain both dorsally and ventrally; parapodial shoulders of anterior setigers retaining stain on anterior border; stain retained between noto- and neurosetae of anterior and middle segments; dorsal surface not staining, but prominent transverse bands extending across venter of anterior segments with intersegmental areas clear. Segmental staining area encompasses and extends beyond transverse band of black pigment speckles.

Etymology. The epithet is from furvus, Latin for dusky or black, referring to the black bands of pigment on the anterior segments of this species.

Remarks. Chaetocirratulus furvus n. sp. differs from other species of the genus, but is somewhat similar to C. neogracilis n. sp., which also occurs in deep water off Peru, in having golden spines along the posterior half of the body. However, the spines of C. furvus n. sp. are smaller and less conspicuous and the pre-setigerous region and pygidial morphology are entirely different; in addition, C. neogracilis n. sp. does not have any pigment on the body as in C. furvus n. sp.

Distribution. Known only from deep water off Peru, 1000 m.