Chaetozone hobsonae Blake, 2015, new species

Chaetozone hobsonae new species

Figures 15‒16

Material examined. Canada, British Columbia, Prince Rupert, off Ridley Island, coll. September 2012, AECOM, by P. Winchell & S. Doner, Van Veen grab: Sta. B05, 19 Sep 2012, 54°12.352ʹN,130°19.966ʹW, 17.7 m, holotype (LACM-AHF Poly 6546), 10 paratypes (LACM-AHF Poly 6547); Sta. B09, 19 Sep 2012, 54°11.698ʹN, 130°18.848ʹW, 7.5 m, 10 paratypes (LACM-AHF Poly 6548); Sta. B23, 20 Sep 2012; 54°11.766ʹN, 130°18.691ʹW, 5.9 m, ca. 200 paratypes (LACM-AHF Poly 6549); Sta. B25, 21 Sep 2012, 54°11.949ʹN, 130°18.672ʹW, 20.1 m, 8 paratypes (LACM-AHF Poly 6550); Sta. B26, 19 Sep 2012, 54°12.070ʹN, 130°18.801ʹW, 12.4 m, 7 paratypes (CMNA 2014- 0 0 17); Sta. B35, 21 Sep 2012, 54°12.281ʹN, 130°18.089ʹW, 26.7 m, 10 paratypes (CMNA 2014- 0018). Southeastern Alaska, Boca de Quadra, Cruise 3BQ, R/V Redoubt, Sta. 100-2, 55°19.2ʹN, 130°29.2ʹW, 95 m, coll. Dec 1979, R.L. Cimberg, Van Veen grab, 6 specimens (LACM-AHF Poly 6551).

Description. A moderate-sized species, holotype and larger paratypes 12–13 mm long, 0.6–0.7 mm wide across anterior setigers and ca. 0.8 mm wide in middle setigers, with about 80–85 setigers. Body typically breaks mid-body, hence many specimens incomplete. Color in alcohol light tan to brown, lacking any distinctive body pigment. Body with narrow crowded segments for two-thirds of body; posterior cinctured setigers not as crowded; body without any prominent swelling or anterior enlargement; with narrow, weakly developed mid-dorsal groove from about setiger 6‒8, continuing posteriorly for about first third of body, not apparent posteriorly; venter flattened, with narrow ventral groove from just posterior to mouth continuing over anterior, middle, and most posterior setigers, absent from far posterior cinctured segments.

Prostomium swollen, enlarged, tapering to triangular and pointed anterior end (Fig. 15 A–B); eyes absent; nuchal organ a narrow slit bordered by thickened pigmented cells, superficially appearing to be an eye (Fig. 15 B). Peristomium elongate with two large rings, best seen laterally, separated from prostomium by deep lateral groove (Fig. 15 A–B). Dorsal tentacles arise near posterior margin of peristomium; first pair of branchiae arising posterior to tentacles just anterior to setiger 1; second pair of branchiae on posterior border of setiger 1, dorsal to notosetae, subsequent setigers with branchiae similarly dorsal to notosetae.

Setiger 1 merging with peristomium approximately same size as subsequent setigers; podial lobes reduced to inconspicuous ridges in anterior setigers, inflated and conspicuous in middle setigers, greatly enlarged with highly elevated ridges and conspicuous armature in posterior setigers; posterior segments separated by deeply cut intersegmental furrows.

Noto- and neurosetae from setiger 1 all capillaries, numbering about 6–8 per fascicle; each seta thickened, relatively smooth, with fibrils sometimes apparent along broadest edge; these capillaries remaining thick and long until far posterior setigers; about half of specimens examined with long, thin, natatory-like notosetae beginning from about setigers 15–20 and continuing along most of body, most prominent in middle setigers. Acicular spines first present from about setiger 50 in notopodia and 35‒40 in neuropodia, numbering 1–3 at first, accompanied by capillaries; in far posterior setigers notopodial spines numbering 7–8, neuropodial spines numbering 10–11, forming complete setal cinctures with 17–19 spines on a side and accompanied by alternating, long, thin capillaries (Figs. 15 D, 16A); spines pointed, slightly curved, notopodial spines directed ventrally, neuropodial spines directed dorsally, spines with weak node or notch at point of emergence from podial lobe (Fig. 15 E–F), with thick borders and fine internal striations (Fig. 16 B–C).

Far posterior setigers narrowing, pygidium with terminal anus and small, flattened ventral disk (Fig. 15 C).

Methyl Green staining pattern. Stain concentrating on dorsum of last peristomial ring and on setiger 1, some stain dorsally on setigers 2–3; some anterior setigers retaining stain ventrally.

Remarks. Chaetozone hobsonae n. sp. is similar to C. columbiana and C. ruffi n. sp. in that a distinct achaetous segment between the peristomium and setiger 1 is not readily apparent due to weakly developed peristomial annuli; because of this, the species is interpreted as lacking an achaetous segment. The species is however, readily recognized in benthic samples due to the triangular prostomium, the pigmented nuchal organs that sometimes resemble eyes, no apparent achaetous segment between the peristomium and setiger 1, acicular spines from mid-body segments, and fully developed posterior cinctures bearing 17‒19 spines on a side, as well as a distinct MG staining pattern. Among, the three closely related species, C. columbiana has 11‒12 spines per posterior cincture, a MG staining pattern, and a terminal cirrus on a short pygidial lobe; C. hobsonae n. sp. has 17‒19 spines per posterior cincture, a MG staining pattern, and pygidial lobe without an cirrus; C. ruffi n. sp. has 20‒22 spines per posterior cincture, no MG staining pattern, and a pygidial lobe without a cirrus. Further, the acicular spines of C. hobsonae n. sp. begin in middle body segments whereas in C. columbiana and C. ruffi n. sp., they begin in the posterior one-third of the body.

Biology and Ecology. Chaetozone hobsonae n. sp. was part of a rich benthic macrofaunal assemblage consisting of more than 400 species of invertebrates from shallow waters (5‒30 m) off Ridley Island, Prince Rupert, BC (Blake, unpublished data). The sediments varied throughout the study area with some sites dominated by sands and others with silt; some samples had shell hash, others wood chips. The habitat diversity contributed to the high faunal diversity. The bivalve Nutricola lordi (Baird, 1863) was the most abundant species in the study area followed by the polychaetes Levinsenia gracilis (Tauber, 1879), Mediomastus californiensis Hartman, 1944, Cossura pygodactylata Jones, 1956, Leitoscoloplos pugettensis Pettibone, 1957, Apistobranchus ornatus Hartman, 1965, and Scoletoma zonata (Johnson, 1901).

Etymology. This species is named for the late Katharine D. Hobson, in recognition of her work on the polychaete fauna of British Columbia.

Distribution. British Columbia and SE Alaska, low water to 95 m; this species is likely more widely distributed in the northeastern Pacific (R.E. Ruff, personal communication).