Chaetozone bathyala Blake, 2015, new species

Chaetozone bathyala new species

Figures 5–6

Chaetozone setosa: Blake & Dean 1973, in part. Not Malmgren 1867.

Material examined. Canadian subarctic: Western Hudson Strait, CSS Hudson cruise 90-023, Sta. 100, collected between 23 September and 16 October 1991, van Veen grab, 63°04.07ʹN, 74°34.00ʹW, 393 m, Western Hudson Strait, holotype (LACM-AHF Poly 6535), 19 paratypes (LACM-AHF Poly 6536). Southern Baffin Bay, R/V Hero Sta. 26 A, 1745 m, 67°49ʹN, 60°46ʹW, coll. J.A. Blake, 16 Aug 1968, 8 specimens (USNM 51222).

Description. A moderate-sized species, holotype complete, 11.5 mm long, 0.8 mm wide across thoracic region, with 80 setigerous segments; all paratypes incomplete but of similar size as holotype. Body widest anteriorly, with short, crowded segments (Figs. 5 A–B, 6A), narrowing posteriorly with segments becoming nearly as long as wide (Fig. 6 D); one of two ovigerous paratypes with abdominal segments nearly moniliform, with body widest anteriorly, narrow crowded segments at least 8–10 times wider than long; segments then becoming about as wide as long in middle body with posterior segments narrowing to about 3–4 times wider than long. Without any distinct dorsal groove along body; with weak ridge along ventral midline (Figs. 5 B, 6B). Color in alcohol light brown with anterior segments sometimes with black pigment pattern (Fig. 6 A), faded in other specimens; Baffin Bay specimens more darkly pigmented.

Prostomium triangular, narrowing to pointed anterior end (Figs. 5 A–B, 6A–C), without eyes; nuchal grooves on posterior margin of prostomium, sometimes pigmented in Baffin Bay specimens. Peristomium complex, with three incomplete anterior annulations producing two relatively large achaetous rings and a narrower posterior ring bearing dorsal tentacles (Fig. 5 A–B); peristomium extending posteriorly to setiger 1, overlying a narrow achaetous segment bearing first pair of branchiae (Fig. 5 A); second pair of branchiae on posterior margin of setiger 1 dorsal and medial to notosetae, subsequent setigers with branchiae arranged in same manner.

Neuropodial acicular spines first appear in anterior third of body: setigers 20–25 on the 80-setiger holotype and setigers 18–20 on an incomplete 50-setiger paratype; spines single at first, then increasing to 3–4 in middle and posterior segments, and up to 10–12 per neuropodium in far posterior cinctured setigers. Notopodial acicular spines first present in far posterior setigers, rapidly increasing to 8–10 per notopodium in far posterior cinctures; cinctures fully developed, with elevated membranes. Acicular spines numbering 18–22 per posterior parapodium, alternating with thin capillaries in dorsal-most and ventral-most positions in notopodia and neuropodia of cinctures, respectively (Fig. 5 C‒D). Individual spines somewhat geniculate, curving toward narrow, bluntly pointed tip; internal striae clearly visible; alternating capillaries narrow (Figs. 5 E, 6F). Two paratypes with long notopodial natatory-like capillaries (Fig. 6 D) and distended abdominal segments with coelom packed with ova; ova measuring up to 156 µm in longest dimension (Fig. 6 G), but average proportions of 137 x 106 µm; other 18 paratypes without natatory-like capillaries or any evidence of gametes.

Pygidium with terminal anal opening and with short, protruding dorsal lobe (Figs. 5 C, 6E).

Methyl Green staining pattern. With distinct MG staining pattern on prostomium and peristomium; all of prostomium except tip staining, with most of peristomium staining forming “mask” over the head region (Fig. 6 C), with grooves separating peristomial rings either staining poorly or not at all.

Biology and ecology. Based on currently available material, C. bathyala n. sp. is limited to deep, cold waters in the Canadian Arctic from 383 to 1745 m. Specimens from shallower depths are referred to other species. The Hudson Strait survey report by McLean et al. (1991) has only limited information on the results of the grab sampling. Sediments are noted to consist of sand and mud, but no actual grain size information is included. The fauna to a depth of 400 m includes several bivalves, polychaetes, and echinoderms, but only bivalves were identified, not specific to any one station. The specimens from southern Baffin Bay, R/V Hero Station 26 were recorded in Blake & Dean (1973). Bottom temperatures were 0.1°C and sediment consisted of thick sticky mud. The most abundant polychaetes occurring with C. bathyala n. sp. were Aricidea suecica Eliason, 1920 (Paraonidae), Cryptosclerocheilus baffinensis Blake, 1972 (Scalibregmatidae), and Jasmineira schudiinni Augener, 1912 (Sabellidae).

Remarks. C. bathyala n. sp. is similar to the type species, C. setosa, in the nature of the peristomium, anterior achaetous segments, fully developed cinctures of posterior spines, and in having a MG staining pattern. However, C. setosa has not been observed with body pigmentation and the ventral surface has a deep groove instead of a ridge; further, C. setosa has capillaries alternating with all spines in the cinctures, whereas C. bathyala n. sp. has them limited to the upper and lower parts of the noto- and neuropodia, respectively. In addition, C. setosa has long, natatory-like setae present in all specimens, whereas in C. bathyala n. sp. they are limited to sexually mature specimens. C. bathyala n. sp. closely resembles C. pigmentata n. sp., also described in this paper, in having a narrow peristomial ring bearing the dorsal tentacles, followed by the first pair of branchiae on a subsequent achaetous segment and the second pair of branchiae appearing on setiger 1. Both species bear body pigment, but in C. pigmentata n. sp. it consists of numerous speckles or patches instead of the diffuse dusky pigment of C. bathyala n. sp. Further, C. bathyala n. sp. has full posterior cinctures of spines with up to 18‒22 spines on a side, whereas C. pigmentata n. sp. has only weak cinctures with no more than 11 spines on a side. C. bathyala n. sp. has a MG staining pattern, whereas C. pigmentata n. sp. has none. The pygidium of C. bathyala n. sp. differs from other species of the genus in having a small dorsal lobe overlying the anal opening instead of the distinct ventral lobe or disk found in most species of Chaetozone.

Among specimens examined by the late Dr. Mary E. Petersen from the collections of the Swedish Museum of Natural History (SMNH) was a single incomplete 39-setiger specimen collected off Newfoundland at coordinates 52°05ʹN, 52°19ʹW, in sand at a depth of 294 m (SMNH 1451). Dr. Petersen’s notes indicate that this specimen was a female with brown pigment on the anterior dorsum to about setiger 17, being darkest on setigers 4‒16. The first neuroacicular spines were on setiger 30 and increased to three or four by setiger 39; notoacicular spines were not yet present and natatory-like capillaries were absent although oocytes were present and measured 85 µm in diameter. These characteristics are mostly consistent with those of C. bathyala n. sp. except for the lack of natatory-like capillaries on a female with eggs.

Etymology. The epithet is derived from the Greek, bathys, for deep, denoting the bathyal depths from which this species was collected.

Distribution. Canadian Arctic and subarctic, in deep water of the Hudson Strait, 393 m and offshore, Baffin Bay, 1745 m; likely record from offshore Newfoundland in 294 m.