Chaetozone cristata Blake 2018, new species

Chaetozone cristata new species

Figures 45–46

Chaetozone sp. 3: Hilbig 2001: 540 (in part); Hilbig et al. 2006: 715, 717, 719, 724 (in part).

Material examined. West Antarctic Peninsula, Palmer Archipelago, Gerlache Strait, R / V Hero Sta. 824-25-1, 23 Mar 1982, 64.253°S, 61.458°W, trawl, 540–605 m, 1 paratype (USNM 1490773); Sta. 824-25-2, 24 Mar 1982, 64.348°S, 61.592°W, VV grab, 92 m, holotype (USNM 1490771) and 7 paratypes (USNM 1490772); Anvers Island, Ryswyck Point, R / V Hero, Sta. 824-32-1, 25 Mar 1982, 64.625°S, 62.853°W, Blake trawl, 640-670 m, 2 paratypes (USNM 1490774).— South Shetland Islands, off King George Island, R / V Polarstern, EASIZ II (ANT-XV/3), coll. B. Hilbig, Sta. 48-299, 14 Mar 1998, 62°15.8ʹS, 58°42.7ʹW, MG, 207 m, 11 specimens (SMF 24933).

Description. A moderate-sized species, holotype complete, 14 mm long, 0.8 mm wide with approximately 100 setigerous segments; paratypes 12–18 mm long, 0.7–0.8 mm wide, with 90–107 setigerous segments. Body elongate, widest in anterior segments, gradually narrowing posteriorly; anterior segments about ten times as wide as long; middle body segments about twice as wide as long; posterior setigers narrowing, about three times as wide as long near posterior end, not moniliform. Dorsum rounded, without groove or ridge; venter somewhat flattened, with prominent mid-ventral groove from anterior through posterior segments (Fig. 46 C–D). Color in alcohol distinctly light tan, no additional pigment apparent anywhere on body.

Prostomium triangular, narrowing apically to pointed tip (Figs. 45A, 46 A–C); eyespots absent; nuchal organs deep notches on posterior lateral margin (Fig. 46C). Peristomium with three more-or-less distinct annular rings surmounted by rounded, grooved dorsal crest (Figs. 45A, 46 A–B); grooves best seen dorsally; peristomium followed by an achaetous segment (Fig. 45A). Dorsal tentacles arising from groove between last peristomial ring and achaetous segment (Fig 45A). First pair of branchiae lateral and slightly posterior to tentacles on posterior margin of achaetous segment (Fig. 45A); second pair of branchiae on posterior edge of setiger 1, dorsal to notosetae (Figs. 45A, 46 A–B); subsequent setigers with branchiae in similar location.

Parapodia of anterior and middle segments reduced to low ridges or mounds from which setae arise; posterior setigers modified with swollen podia, cinctures reduced, lacking high-elevated membranes present in related species; acicular spines in these podia forming prominent armature (Figs. 45B, 46E). Anterior setae all capillaries numbering 8–10 in noto- and neuropodia with notosetae longer than neurosetae; capillaries of middle segments similar in number. Long, thin, natatory-like capillaries present in middle and posterior segments of gravid specimens. First appearance of acicular spines along body variable, somewhat size dependent. Neuropodial acicular spines first appear in posterior body segments from setigers 57–70 (57 in holotype); notopodial spines from setigers 70–96 (70 in holotype). Noto- and neuropodial spines initially numbering 1–3 per fascicle with 5–6 capillaries; posterior full cinctures from last 6–10 setigers with up to 9–10 spines in noto- and neuropodia, up to 19–20 spines on a side (Fig. 46E); spines alternating with long, thin capillaries. Individual neuroacicular spines curved, with narrow blunted tip (Fig. 45D); each with internal core clearly visible in transmitted light (Fig. 46E); notoacicular spines longer, narrower than neuroacicular spines, with weakly curved to straight shaft (Fig. 45C).

Body terminating in simple pygidium with broad, rounded lobe ventral to anus (Figs. 45B, 46D).

Variability. Some specimens with peristomial annulations less distinct resulting in peristomium and dorsal crest appearing smooth; annular grooves and location of dorsal tentacles and branchiae revealed, however, after staining with Shirlastain A or Methyl Green.

Methyl Green stain. Posterior half of peristomium retains stain; rest of body stains uniformly; some specimens with weak ventral bands on some anterior parapodia; other specimens not staining at all.

Etymology. The species name cristata is from the Latin cristatus for crested, referring to the prominent dorsal crest on the peristomium of this species.

Remarks. Among Antarctic species of Chaetozone, C. cristata n. sp. occurs in relatively shallow waters and is readily identified by the three peristomial rings and prominent peristomial crest. In addition, the full posterior cinctures contain shorter curved spines in the neuropodia and longer, thinner notopodial spines that are nearly straight. Furthermore, C. cristata n. sp. has a Methyl Green staining pattern on the peristomium of most specimens; related Antarctic species with full cinctures lack a prominent Methyl Green pattern.

Habitat & biology. R/V Hero samples from the West Antarctic Peninsula suggest that Chaetozone cristata n. sp. is associated with a mixed sediment: Sta. 824-25-2 (gravel, mud, and rocks); Sta. 824-32-1 (foliaceous bryozoa with mud and pebbles). One paratype from Hero Sta. 824-25-2 (USNM 1490772) has large eggs, up to 152 µm in diameter.

Distribution. West Antarctic Peninsula, 92– 670 m.