Chaetozone anasima Doner & Blake 2006

Chaetozone anasima Doner & Blake, 2006

Figure 17

Chaetozone setosa Blake et al. 1998b: C-1 (in part). Not Malmgren, 1867.

Chaetozone anasimus Doner & Blake, 2006: 67–68., figs. 2, 5C, G).

Chaetozone anasima: Blake & Levesque 2017: 572–575.

Material examined. (208 specimens) Northeastern USA, Gulf of Maine, Georges Bank, MMS Benthic Infauna Monitoring Program, coll. G.W. Hampson, Chief Scientist: Sta. 14A: Cruise M-6, Rep. 2, 20 Nov 1982, 41°57.5′W, 68°31.2′W, 168 m, (1, USNM 1660979); Cruise M-7, Rep. 1, 06 Feb 1983, 41°57.5′W, 68°31.0′W, 168 m (1, USNM 1660980); Rep. 4 (2, USMM 1660981); Cruise M-8, Rep. 5, 14 May 1983, 41°57.5′W, 68°31.1′W, 170 m (1, USMM 1660982); Cruise M-9, Rep. 1, 13 Jul 1983, 41°57.5′W, 68°31.0′W, 179 m (1, USMM 1660983).— Massachusetts Bay, MWRA Harbor and Outfall Monitoring Program: 1995 August Survey, Sta. FF-05: Rep. 2, Aug 1995, 42°08.00′N, 70°25.35′W, 61 m (11, MCZ 161922). Sta. FF-11: Rep. 2, Aug 1995, 42°39.50′N, 70°30.00′W, 87 m (22, MCZ 161923); Rep. 3 (21 MCZ 161924). 1997 August Survey, Sta. FF-04: Aug 1997, Rep. 1, 42°17.30′N, 70°25.50′W, 87 m (31, MCZ 161925); Rep. 2 (21, MCZ 161926); Rep. 3 (61, MCZ 161927). Sta. FF-05: Rep. 2, Aug 1997, 42°08.00′N, 70°25.35′W, 61 m (20, MCZ 161928); Rep. 3 (10, MCZ 161929). Sta. FF-09: Rep. 1, Aug 1997, 42°18.75′N, 70°39.40′W, 49 m (3, MCZ 161930); Rep. 2 (5, MCZ 161931). August 2002 Survey, Sta. FF-11: Rep. 2, Aug 2002, 42°39.50′N, 70°30.00′W, 88 m, 3 on SEM Stubs (MCZ 161932). 2006 August Survey, Sta. FF-04: Rep. 3, 03 Aug 2006, 42°17.296′N, 70°25.30′W, 88 m (16, MCZ 161933).

Description. A moderately sized species, 9–12 mm long, 0.5– 1 mm wide for 65–90 setigers. Body thick, robust in anterior two-thirds, then tapering posteriorly. Dorsum rounded with narrow groove (Fig. 17A); venter flattened with broad channel or groove along most of body (Fig. 17B–D). Anterior segments short, crowded about ten times wider than long; posterior segments longer, about 2.5 times as wide as long. Color in alcohol light tan, with no body pigments evident.

Pre-setiger region short, compact, about as wide as long and as long as first six setigers (Fig. 17A–B). Prostomium short, conical, pointed (Fig. 17A), sometimes with tip directed dorsally (Fig. 17B); eyespots absent; nuchal organs present on lateral surface of peristomium just anterior to oral opening, as a ciliated oval groove (Fig. 17B, inset). Peristomium with two lateral grooves producing three rings surmounted by broad dorsal crest (Fig. 17A–B). Dorsal tentacles arising from near posterior margin of peristomium with first pair of branchiae lateral and slightly posterior to tentacles (Fig. 17A). First branchiae appearing to arise from groove between peristomium and setiger 1 in some views (Fig. 17B); subsequent setigers with branchiae arising dorsal to notosetae (Fig. 17A).

Parapodia of anterior and middle setigers lateral enlargements, forming distinct shoulders along body between notopodium and rounded dorsal surface (Fig. 17A); setae arising from posterior margin of each noto- or neuropodium. Parapodia of posterior 20–25 setigers becoming narrow, and elevated forming distinct cinctures bearing acicular spines and capillaries (Fig. 17D, G). Noto- and neurosetae of anterior and middle body segments all capillaries, numbering about 8–12 per fascicle; long natatory-like capillaries variably present on some specimens, not associated with reproduction. Acicular spines first present from about setiger 50–60 in neuropodia and 55–65 in notopodia. In most specimens posterior setigers with 10–14 notopodial spines and 6–10 neuropodial spines or with 16–24 spines on a side producing full cinctures; spines accompanied by alternating thin, smooth capillaries, most longer than spines (Fig. 17D–E, G). Spines with narrow pointed tips that bend back and merge with shaft of spine on concave edge; recurved bent tips only apparent in light microscopy, not visible in SEM where spines appearing with curved tip (Fig. 17H). Cinctured segments with low elevated membranes from with setal fascicles emerge (Fig. 17G).

Pygidium with rounded lobe or inflated cushion ventral to anal opening (Fig. 17E–F).

Methyl green staining. Base of prostomium stains; rest of body stains lightly with no pattern after differentiation.

Remarks. Chaetozone anasima belongs to the C. curvata and occurs in inner and outer shelf habitats, whereas two additional new species described in this study, C. adunca n. sp. and C. brychiata n. sp., both occur in deepwater sediments. Morphological similarities and differences among the nine species in the C. curvata group are presented in Table 3.

Among species in the Chaetozone curvata group, C. anasima and five other species have three peristomial rings (Table 3). Of these, only C. anasima and Chaetozone gesae Blake, 2018 from off Chile, have a dorsal crest. However, C. anasima has full posterior cinctures with up 16–24 spines on a side instead of partial cinctures with 13–15 spines as in C. gesae. In addition, C. gesae is recorded as having the first and second pair of branchiae both occurring on setiger 1, whereas in C. anasima, the first branchiae occur on the posterior margin of the peristomium.

Among local species of nearshore and continental shelf species of Chaetozone, C. anasima, apart from the recurved tips on the acicular spines, may be easily recognized by the relatively short pre-setiger region with three peristomial rings and a prostomium that is typically turned upward. In contrast, Chaetozone hystricosa (Doner & Blake, 2006), with which C. anasima may occur, has an elongate, smooth pre-setiger region, not interrupted by annular rings, that tapers to a narrow anteriorly directed prostomium.

Distribution. Northeastern USA, Massachusetts Bay, 49–90 m; Gulf of Maine, 168– 179 m.