Chaetozone brychiata Blake 2022, new species

Chaetozone brychiata new species

Figures 18–19

urn:lsid:zoobank.org:act: E42B29D7-CA25-472D-9486-0A240F06E7C3

Cirratulidae sp. 1: Maciolek et al. 1987a: D-2.

Chaetozone sp. 10: Maciolek et al. 1987a: D-2 (in part).

Material examined. (7 specimens) Off Delaware, U.S. Mid-Atlantic ACSAR Program, coll. R. Petrecca, Chief Scientist. Sta. 10: Cruise Mid-4, Rep. 1, 19 May 1985, 37°51.76′N, 72°20.01′W, 2095 m, holotype (USNM 1660984), 1 paratype (USNM 01660985); Cruise Mid-1, Rep. 1, 07 May 1984, 37°51.52′N, 73°17.57′W, 2095 m, 1 paratype (USNM 1660986). Sta. 2: Cruise Mid-4, Rep. 2, 17 May 1985, 38°35.66′N, 72°53.80′W, 2011 m (1 juvenile, USNM 1660987). Sta. 3: Cruise Mid-6, Rep. 1, 12 Nov 1985, 38°36.73′N, 72°51.62′W, 2064 m, 2 paratypes (USNM 1660988).— Off New England, Lydonia Canyon, U.S. North Atlantic ACSAR Program, coll. G.W. Hampson, Chief Scientist. Sta. 8: Cruise NA-4, Rep. 1, 25 Nov. 1983, 40°10.21, 67°37.24′W, 2084 m (1, USNM 1660989).

Description. A small species, holotype (USNM 1660984) complete, with 65 setigers, 5.1 mm long and 0.35 mm wide; paratype (USNM 1660985) incomplete, with 62 setigers, 6.5 mm long and 0.44 mm wide; another paratype (USNM 1660988) with 70 setigers, 6.54 mm long and 0.37 mm wide. Body generally of similar width across anterior and middle setigers, tapering posteriorly; thoracic segments crowded, only slightly enlarged. Individual segments of anterior and middle segments short, about 6–7 times wider than long at first, posterior setigers longer, only about three times wider than long. No dorsal or ventral grooves along body; mid-ventral ridge consisting of a row of paired swellings at junction of each segment mid-ventrally, present along entire body. Posterior segments with reduced cinctures, bearing acicular spines without with deep intersegmental grooves or elevated membranes. Color in alcohol light tan; no apparent pigmentation.

Pre-setiger region relatively short, only slightly longer than wide; long, narrow, smooth, about as long as first ten setigers (Figs. 18A, 19A). Prostomium conical, triangular, with pointed tip; eyespots absent; nuchal organs narrow slits on posterior lateral margins. Peristomium rectangular, medially extending dorsally over setiger 1; laterally with one deep groove producing two peristomial rings, but these not crossing dorsal surface; dorsum with broad dorsal crest extending from prostomium to posterior margin (Fig. 18A). Dorsal tentacles arising medially from posterior margin of peristomium, with first pair of branchiae on setiger 1, posterior and lateral to tentacles (Fig. 18A); second pair dorsal to notosetae on setiger 2 (Fig. 18A); subsequent branchiae from setiger 3 in same location dorsal to notosetae.

Parapodia of anterior and middle segments reduced to low ridges or mounds from which setae arise; posterior parapodia similar, lacking deep intersegmental grooves and elevated membranes (Figs. 18B, 19D). Setiger 1 and thoracic segments with 12–15 capillaries in notopodia and neuropodia; capillaries mostly of moderate size; long, natatory-like capillaries absent. Acicular spines first present in holotype from setiger 45 in notopodia and setiger 36 in neuropodia; paratype (USNM 1660988) with notopodial spines from setiger 58 and neuropodial spines from setiger 45; spines 2–3 at first, increasing posteriorly into partial cinctures over last 12–15 setigers with 4–5 spines in notopodia and 7 in neuropodia or up to 11–12 spines on a side; spines alternating with capillaries as long as or slightly longer than spines; cinctures not complete, leaving broad dorsal gap between notopodia (Figs. 18B, 19D). Spines unusually long, narrow, curving and tapering gradually to narrow hooked tip with tip of hook curving inwardly and merging with shaft (Figs. 18C, 19B–C).

Body narrowing in last few segments, terminating in simple pygidium with a small, semicircular disk bearing two short anal cirri (Figs. 18B, 19D); specimen from North Atlantic Sta. 8 (USNM 1660989) damaged, with only a single lateral protuberance evident on pygidial disk.

Description of Juvenile. A juvenile (USNM 1660987) believed to be this species has 13 setigers and is only 0.8 mm long. The last setiger bears a single recurved acicular spine. The pygidium has a flattened disk bearing two anal cirri.

Methyl green staining. No pattern, stain not retained.

Remarks. Chaetozone brychiata n. sp. is the ninth species to be described in the C. curvata group, with acicular spines with a shaft that tapers to a pointed tip that curves downward and merges with the shaft. Chaetozone brychiata n. sp. differs from all other species Chaetozone by having two short anal cirri arising from a semi-circular pygidial disk. The only other cirratulids having two short anal cirri are in the genus Caulleriella. In addition, the acicular spines of C. brychiata n. sp. are unusually long and narrow, typically of the same width as accompanying capillaries.

Etymology. The epithet brychiata is from the Greek, brychios, “from the deep”, in reference to the deep-sea habitat of this rare species.

Distribution. U.S. Atlantic continental slope, off Delaware, 2011–2095 m; U.S. North Atlantic slope, Lydonia Canyon, 2084 m.