Chaetozone camasetosa Blake, 2015, new species

Chaetozone camasetosa new species

Figures 17‒18

Material examined. 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, holotype (LACM-AHF Poly 6552), one paratype (LACM-AHF Poly 6553). Prince Rupert, British Columbia, off Ridley Island, coll. September 2012, AECOM by P. Winchell & S. Doner, few specimens mixed with C. hobsonae n. sp., mostly incomplete, 12‒20 m (JAB).

Description. A moderate-sized species, holotype complete, 6.0 mm long, 0.4 mm wide for 65 setigerous segments; paratype in two pieces, 10.5 mm long, 0.5 mm wide for 64 setigerous segments; Prince Rupert specimens small, mostly incomplete. Color in alcohol light tan to brown, lacking any distinctive body pigment. Body generally thick, with narrow segments throughout, middle body segments widest; last 12‒15 setigers formed into distinct cinctures with high membranes bearing spines. Dorsum rounded, with narrow and shallow dorsal groove apparent from about setiger 20, continuing along body until cinctured posterior segments; venter somewhat flattened, with well-developed ventral groove present from about setiger 20, continuing through middle body segments, not apparent posteriorly.

Prostomium swollen posteriorly, narrowing anteriorly to triangular, blunted margin (Fig. 17 A); eyes absent; small slit-like nuchal organ present, not pigmented; peristomium with three nearly equal rings, merging with posterior margin of prostomium (Fig. 17 A); achaetous segment absent; dorsal tentacles arising from posterior margin of posterior ring; first pair of branchiae lateral and slightly posterior to tentacles on anterior margin of setiger 1 (Fig. 17 A); second pair of branchiae on posterior edge of setiger 1, dorsal to notosetae; subsequent setigers with branchiae in similar location.

Setiger 1 of approximately same size as last peristomial annulation and following segments; podial lobes reduced to inconspicuous ridges in anterior setigers; inflated and conspicuous in middle setigers, greatly enlarged with elevated ridges and conspicuous armature in posterior setigers (Fig. 17 B); posterior segments separated by deeply cut intersegmental furrows (Fig. 17 B).

Noto- and neurosetae from setiger 1 all capillaries; notosetae 9–10 per fascicle, neurosetae 6–8 per fascicle; each capillary thickened, with no distinct fibrils apparent along edge; middle body segments with long, natatory-like notosetae. Acicular spines first present from about setiger 30 in neuropodia and 40 in notopodia of holotype and setiger 40 in neuropodia and 45 in notopodia of paratype; spines numbering 2–3 at first, accompanied by an equal number of thin capillaries; in far posterior setigers notopodial spines numbering 9–11 and neuropodial spines numbering 11–12, forming nearly complete cinctures with spines numbering 20–23 on a side and accompanied by alternating thin capillaries (Fig. 18 A, B); spines with sharply pointed tip that curves back and adheres to shaft (Fig. 17 C), with weak node or notch at point of emergence from podial lobe (Fig. 18 C).

Last few cinctured setigers narrowing to posterior end; pygidium with terminal anus and small flattened ventral lobe (Fig. 17 B).

Methyl Green staining pattern. Tip of prostomium staining, last two peristomial rings staining, with some streaks extending dorsally onto expanded anterior peristomial ring.

Biology. Paratype with body full of oocytes about 70 µm in diameter.

Remarks. The curved tip of the posterior spines of C. camasetosa n. sp. occurs in a small group of Chaetozone species that includes C. curvata Hartmann-Schröder, 1965, from Chile, C. commonalis Blake, 1996 from California shelf depths, C. allanotai from California deep-water slope depths, and C. anasima Doner & Blake, 2006 from offshore New England. Of these, C. curvata and C. commonalis have the first pair of branchiae on setiger 1, whereas C. allanotai, C. anasima, and C. camasetosa n. sp. have an extra pair of branchiae lateral and posterior to the dorsal tentacles on the anterior margin of setiger 1, as well as a pair on the posterior margin of the same setiger. This condition suggests that a segment has been lost or fused with setiger 1. These three species differ from one another in that C. anasima lacks distinct peristomial rings including any demarcation or annulation between the peristomium and setiger 1; whereas, both C. camasetosa n. sp. and C. allanotai have two distinct rings. The latter two species appear to be closely related to one another and may be a shallow-water to deep-water sibling species pair. In C. camasetosa n. sp., the two peristomial rings are strongly set off from one another by deep annulations and also separated from the swollen posterior margin of the prostomium. In C. allanotai, the peristomial rings are not strongly demarcated and, in addition, the first pair of branchiae actually occurs on setiger 1. Both species have different MG staining patterns on the prostomium and peristomium. C. allanotai appears to be limited to continental slope depths of 1800‒3100 m and is a dominant species in the 2700‒2850 m depth range from sites offshore northern California (Blake 2006). The specimens of C. camasetosa n. sp. examined here are from shelf depths of up to 95 m.

Etymology. The epithet is from the Latin camur, for crooked or curving inward, combined with seta referring to the manner in which the tip of the posterior spines curve inward merging on the concave side of the shaft and forming an apparent blunt tip.

Distribution. Southeastern Alaska to British Columbia, subtidal, 12‒ 95 m. The specimens here suggest that they fragment easily and as such cannot be readily identified without the posterior modified spines.