Chaetozone ruffi Blake, 2015, new species

Chaetozone ruffi new species

Figures 9–10

Chaetozone setosa: Busdosh 1984. Not Malmgren 1867.

Material examined. Alaskan Arctic, Beaufort Sea, Prudhoe Bay, 0 5 Aug 1983, 70°23.9ʹN, 148°26.0ʹW, 3 m, push cores, coll. M. Busdosh, Waterflood 6 project, R/V Annika Marie, Sta. 15-1, holotype (LACM-AHF Poly 6540), 3 paratypes (LACM-AHF Poly 6541).

Description. A moderate-sized species, holotype 12 mm long, 1.0 mm wide with 96 setigerous segments; paratypes similar in size with 90–100 setigers. Body expanding slightly in anterior segments, narrowing gradually along body; posterior third of body with full cinctures of spines. Middle body dorsoventrally flattened, with deep ventral groove continuing to near posterior end; mid-dorsal groove present along most of body (Figs. 9 A, 10A–B), becoming deeper and more distinct in posterior setigers where elevated membranes and cinctures of spines overlap and enhance groove. Color in alcohol light tan with no body pigment.

Prostomium narrow, pointed on anterior margin (Fig. 9 A–B), with slit-like nuchal organ on posterolateral margin (Fig. 9 B); eyes absent. Peristomium broad, with 2–3 weak annulations, forming one large anterior ring and two narrow posterior rings; all rings weakly defined (Fig. 9 A–B) and variable in size and development between specimens; distinct achaetous segment not apparent; last peristomial ring bearing tentacles and first pair of branchiae, with latter arising lateral to tentacles (Fig. 9 A–B). Second pair of branchiae arising from setiger 1, continuing on subsequent segments; branchiae of anterior third of body long, thick, branchiae of middle and posterior segments, short and thin where present.

Anterior noto- and neurosetae all simple capillaries arranged in single rows of 6–8 notosetae and neurosetae; capillaries increasing in middle body segments to 15 or more in notopodia and 10–12 in neuropodia; some capillaries long, but extremely long natatory-like capillary setae absent in mature individuals.

Neuropodial acicular spines from setigers 56–57 or posterior third of body, first spines single, in ventral-most position in fascicle, then increasing to 9–11 over next 20–22 setigers replacing all but dorsal-most capillaries; very thin capillaries appearing in last 15 or so posterior-most segments, alternating with spines. Notopodial acicular spines from setigers 58–65, with first spines in dorsal-most location of fascicle, increasing to 9–11 posteriorly, but not replacing capillaries as in neuropodia, instead, capillaries retained and alternate with spines but become very thin in far posterior cinctures. Posterior segments with well-developed elevated membranes and 10–11 spines in both noto- and neuropodia, forming full cinctures on each segment, with notosetae overlapping at dorsal midline (Fig. 10 B–D). All cinctured segments with spines alternating with long, thin capillaries; each spine thickened basally, curving, tapering to blunt tip (Figs. 9 D–E, 10D–E); notopodial spines generally longer than neuropodial spines, with neuropodial spines in ventral-most position shorter, curved, weakly geniculate.

Pygidium with terminal anus and small, rounded ventral lobe (Figs. 9 C, 10C).

Methyl Green staining pattern. No pattern.

Biology and ecology. This species occurred in shallow, sandy silt sediments of Prudhoe Bay. Other commonly associated invertebrates included the polychaetes Tharyx alaskensis n. sp., Marenzellaria viridis (Verrill, 1873), Prionospio cirrifera, Ampharete vega (Wirén, 1883), and the amphipod Monoporeia affinis (Lindström, 1855). Coelomic oocytes present in the holotype and paratypes, ca. 60‒80 µm in longest dimension.

Remarks. Due to weakly developed peristomial annuli, a distinct achaetous segment between the peristomium and setiger 1 could not be discerned in Chaetozone ruffi n. sp.; therefore, both the paired tentacles and first pair of branchiae are interpreted as arising from the posterior margin of the peristomium. Both the neuropodial and notopodial spines begin in the posterior third of the body rather than more anteriorly as is typical for related species. The posterior cinctures form highly modified posterior segments in this species; the notopodial spines and notopodial membranes overlap mid-dorsally enhancing the dorsal groove.

Among species known from the NE Pacific and the North American Arctic, the species closest to C. ruffi n. sp. are C. columbiana Blake 1996 from off Oregon and Washington and C. hobsonae n.sp. from British Columbia and SE Alaska. Each of these species lack a distinct achaetous segment anterior to setiger 1 and the dorsal tentacles and first pair of branchiae arise from the posterior margin of the peristomium. Chaetozone ruffi n. sp. has up to 22 posterior acicular spines on each side; C. columbiana has 11‒12; and C. hobsonae n. sp. has 17–19. Further, both C. columbiana and C. hobsonae have distinctive MG staining patterns while C. ruffi n. sp. has none. In lacking a distinct achaetous segment that can be discerned on the peristomium, C. ruffi n. sp. is also similar to C. hystricosa Doner & Blake, 2006, from off New England; however, C. hystricosa has only 12–13 acicular spines on each side in posterior setigers, whereas C. ruffi n. sp. has up to 22 acicular spines.

Etymology. This species is named for my friend and long-time colleague, Mr. R. Eugene Ruff. Gene provided much of the material and data presented in this paper and contributed valuable information relative to his extensive experience with the benthos of northeastern Pacific and Alaska.

Distribution. Alaskan Arctic in shallow water, 3 m.