Chaetocirratulus tomaculus Blake 2022, new species

Chaetocirratulus tomaculus new species

Figures 12–14

urn:lsid:zoobank.org:act: D1107CE4-A9FD-45B8-A942-937217AF999F

Chaetozone gayheadia: Hartman & Fauchald 1971 (in part). Not Hartman 1965.

Material examined. (147 specimens) Off New England Near Veatch Canyon, R/ V Chain Sta. Cruise 50, coll. R. R. Hessler, Chief Scientist, Sta. Ch 87: coll. 06 Jul 1965, 39°48.7′N, 70°40.8′W, 1102 m, holotype (LACM-AHF 12722), 11 paratypes (LACM-AHF Poly 12728); 130+ specimens including juveniles (LACM-AHF Poly 12729).— Off New England, U.S. North Atlantic ACSAR Program, coll. G.W. Hampson, Chief Scientist. Sta. 3: Cruise NA-3, Rep. 3, 03 Jul 1985, 41°01.43′N, 66°20.21′W, 1328 m (1, USNM 1660943); Cruise NA-5, Rep. 3, 28 Apr 1986, 41°01.35′N, 66°20.24′W, 1355 m (1, USNM 1660940). Sta. 9: Cruise NA-1, Rep. 2, 12 Nov 1984, 39°50.44′N, 70°01.76′W, 1228 m (1, USNM 166041). Sta. 10: Cruise NA 4, Rep. 2, 27 Nov 1985, 39°48.07ʹN, 70°05.32ʹW, 1234 m (1 juv., USNM 1660939); Rep. 3, 27 Nov 1985, 39°48.10ʹN, 70°05.33ʹW, 1219 m (1, USNM 1660942).

Description. A moderately sized species, with a thick grub-like or sausage-shaped body, widest in middle segments, tapering at anterior and posterior ends (Fig. 13A). Holotype (Fig. 12A–B) with 48 setigers, 9.9 mm long and 1.0 mm wide across middle segments. Largest paratype with 52 setigers, 14.1 mm long and 2.1 mm wide (Fig. 13A). Parapodia located laterally along body with intersegmental grooves well developed throughout. Dorsal surface elevated above parapodia, rounded with surface partitioned into rows of longitudinal ridges or blocks along most of body (Figs. 12C, 14B); venter similarly configured with prominent intersegmental grooves, ridges and blocks. Dorsal and ventral grooves absent, but with a narrow ridge along venter extending from peristomium to posterior end. Color in alcohol tan; with minute inconspicuous pigment spots present or absent on ventral surface of peristomium posterior to mouth and first two setigers.

Pre-setiger region short, about as wide as long; as long as first 4–5 setigers (Fig. 12A). Prostomium short, wide, broadly rounded anteriorly (Figs. 12A–B, 13A–C, 14B); smaller specimens with prostomium weakly triangular with narrower tip (Fig. 14E–G); eyespots absent; nuchal organs at posterior lateral margins, mostly hidden by peristomium. Peristomium with three rings, complete dorsally separated by distinct grooves lacking dorsal crest (Fig. 12A); incomplete ventrally (Fig. 12B); first peristomial ring surrounding prostomium dorsally and ventrally forming posterior lip of mouth and merged with second ring forming a large relatively smooth peristomial area only separated indistinctly by a shallow transverse groove (Figs. 12B, 13C); merged first and second ring narrowing, then continuing posteriorly overlapping third ring and middle of first 2–3 anterior setigers, continuing posteriorly as narrow mid-ventral ridge along entire body (Fig. 12B). Dorsal tentacles arise from posterior margin of third peristomial ring and with first pair of branchiae lateral to tentacles (Fig. 12A). Subsequent segmental branchiae occur dorsal to notosetae on posterior margin of individual parapodia. Branchiae missing on many specimens with stubs or scars present to about mid-body.

Parapodia of anterior segments bearing short, narrow noto- and neuropodia from which setae arise. Podia less conspicuous in middle and posterior segments. Setae include long, smooth capillaries and acicular spines. Capillaries numbering 19–22 per noto- and neuropodia in anterior setigers, reduced to 6–7 in middle segments and 2–3 in posterior setigers. Acicular spines in far posterior neuropodia first occurring in setigers 39–41 in largest specimens with 45–52 setigers; notopodial spines (Fig. 12D) in a few posteriormost setigers of same specimens, but irregular and may be absent on some setigers. Neuropodial spines 2–3 per neuropodium, each with straight shafts tapering to bluntly rounded tips (Figs. 12E–F; 13E, 14D); notopodial spines when present, each with slightly curved shafts tapering to sharply pointed tips (Fig. 12D); spines accompanied by 1–3 capillaries.

Pygidium with narrow rounded ventral lobe (Figs. 12C, 13D); with 4–5 short dorsal lobes surrounding anal opening (Figs. 12C).

Variability. Smaller specimens are narrower and thick, but with less of a sausage shape; some thick anteriorly, tapering posteriorly. Four smaller specimens are illustrated: Fig.14 E (2.2 mm long, 0.44 mm wide with 21 setigers); Fig. 14 F (2.8 mm long, 0.38 mm wide with 31 setigers) Fig. 14G (2.8 mm long, 0.43 mm wide with 26 setigers; Fig. 14H (3.6 mm long, 0.39 mm wide with 30 setigers). Acicular spines first present from setiger 6–10 in neuropodia and 8–10 in notopodia in these specimens. Specimen from NA-4, Sta. 10, comma-shaped, 3.5 mm long, 0.5 mm wide, with 33 setigers and first hooks in neuropodia from setiger 10.

Methyl green staining. Pre-setiger region with distinctive pattern; posterior half of prostomium with broad dorsal band; anterior margin not stained. Peristomium stained laterally, leaving dorsal surface unstained; two bands of lateral stain continuing across venter; similar lateral and ventral bands present on 4–6 anterior setigers (Fig. 14A–C).

Abbreviations: dT, dorsal tentacle; Ne, neuropodial; No, notopodial; set, setiger.

Remarks. Globally, Chaetocirratulus tomaculus n. sp. is most similar to the type species Chaetocirratulus andersenensis (Augener, 1932) from Antarctica in having a broadly rounded prostomium, three peristomial rings and acicular spines limited to far posterior segments (Blake 2018). However, C. andersenensis has a distinctly short fusiform-shaped body and blunt-tipped acicular spines in both noto- and neuropodia, whereas C. tomaculus n. sp. has an elongate sausage-shaped body and blunt-tipped spines limited to neuropodia; notopodial spines are few and taper to a sharply pointed tip. In addition, the three peristomial rings of C. andersenensis are complete both dorsally and ventrally, whereas the rings are incomplete ventrally in C. tomaculus n. sp. with the first two rings merged, narrowing posteriorly and overlapping the third ring and several anterior setigers.

Locally, Chaetocirratulus tomaculus n. sp. is similar to C. hessleri n. sp. in having three peristomial rings, acicular spines limited to posterior setigers, and a similar methyl green staining pattern. However, C. tomaculus n. sp. has a broadly rounded prostomium instead of one that is triangular and narrows to an apical point, all three peristomial rings are complete dorsally instead of incomplete with a dorsal crest in C. hessleri n. sp. All four U.S. Atlantic species are compared in Table 2.

Biology. One large paratype with coelom packed with oocytes measuring 100–120 µm in diameter. No sediment data is available from Station Ch 87.

Etymology. The epithet, tomaculus, is from the Latin, tomacina, for a kind of sausage, in reference to the sausage-shaped body of this species.

Distribution. Off New England, continental slope depths of 1102–1328 m.