Heterospio alata Blake & Maciolek 2023, new species

Figures 14–15

urn:lsid:zoobank.org:act: 928F46F1-0540-4698-AD4D-D0A209AC23F8

Material examined. (16 specimens) South China Sea, off Brunei, Island of Borneo, Site CA1, R / V Emma, coll. J.A. Blake, Chief Scientist, BC, Sta. 55, 01 Jun 2011, 5.728°N, 114.246°E, 1150 m, holotype (MCZ 163704); 1 paratype (MCZ 163705); Sta. 10, 06 Jun 2011, 5.865°N, 114.209°E, 1453 m (1, MCZ 163706); Sta. 44, 02 Jun 2011, 5.472°N, 114.153°E, 1294 m, 1 paratype (MCZ 163707); Sta. 46, 02 Jun 2011, 5.801°N, 114.303°E, 1234 m, 2 paratypes (MCZ 163708); Sta. 48, 02 Jun 2011, 5.758°N, 114.257°E, 1219 m, 3 paratypes (MCZ 163709); Sta. 49, 02 Jun 2011, 5.740°N, 114.233°E, 1199 m, 1 paratype (MCZ 163710); Sta. 53, 01 Jun 2011, 5.679°N, 114.193°E, 1212 m 1 paratype (MCZ 163711); Sta. 54, 09 Jun 2011, 5.703°N, 114.220°E, 1171 m (1 juv, MCZ 163712); Sta. 58, 01 Jun 2011, 5.727°N, 114.272°E, 1127 m 1 paratype (MCZ 163713); Sta. 59, 31 May 2011, 5.433°N, 114.162°E, 1114 m (1 juv, MCZ 163714).— Site CA2, R / V Emma, coll. P.A. Neubert, Chief Scientist, BC, Sta. TU3, 24 Jun 2011, 19.898°N, 113.747°E, 1267 m, 1 paratype (MCZ 163715); Sta. TU5, 24 Jun 2011, 5.231°N, 113.747°E, 1224 m, 1 paratype (MCZ 163716).

Description. A moderately sized species, most specimens incomplete, one small specimen complete in two parts. Body elongate, narrow, anterior crowded segments slightly narrower than thicker elongate abdominal segments; posterior fragments with bulbous posterior end. Holotype (MCZ 163704) an anterior fragment with 16 setigers, 14.8 mm long, 0.22m wide across thorax; 0.24 wide across abdomen; paratype (MCZ 163708): 13 setigers, 11.6 mm long, 0.24 across thorax; 0.29 across abdomen; small paratype (Sta. 49): 15 setigers, 5.8 mm long, 0.13 mm wide across thorax, and 0.15 mm across abdomen. One small paratype (MCZ 163708) complete, in two parts with 24 setigers: 14.4 mm long, 0.12 mm wide across thorax; 0.15 mm wide across abdominal setigers (includes nine thoracic, 11 abdominal, and a bulbous posterior section with four setigers with hooks). Color in alcohol light tan; pigment entirely absent.

Pre-setiger region triangular in shape, short, about as long as first two thoracic setigers (Figs. 14A–C, 15B). Prostomium pear-shaped or triangular, tapering to narrow rounded tip; eyespots absent, nuchal organs narrow slits along posterior margin (Fig. 14C). Peristomium with a single large achaetous ring, complete ventrally, but interrupted dorsally by narrow dorsal crest extending from prostomium to border of setiger 1 (Figs. 14A, C, 15B). Dorsal tentacles absent; scars not clearly evident, but likely in notch between dorsal crest and anterior borders of peristomium. Mouth arising ventrally at posterior margin of prostomium, consisting of narrow vertical slit between four lateral lobes (Fig. 14B); proboscis sometimes present as rounded lobes.

Thoracic region defined by eight short crowded setigers followed by elongate setiger 9 about as long as setigers 1–7 (Fig. 14A). Transition from thoracic segments with defined dorsolateral setal fascicles to abdominal segments denoted by setae arising from broad cincture-like rows mostly surrounding anterior margin of each segment occurs at setiger 11.

Branchiae or their stubs present on setigers 2–3 (Fig. 14A, C) not observed on subsequent segments; most branchiae when present short, thick, but with a few longer, thin, rounded in cross section, tapering to rounded tip (Fig. 15A, C).

All parapodia biramous with setae emerging from near anterior edge of each segment. Thoracic setigers 1–10 with dense fascicles of setae in dorsolateral locations on each segment; thoracic notosetae numerous capillaries in dense fascicles consisting of five or more curved rows; neurosetae of setiger 1 with about six curved bidentate spines (Fig. 14E) and an equivalent number of capillaries; neurosetae of setigers 2–10 numerous capillaries. Bidentate hooks of setiger 1 curved, tapering to pointed tip; apical tooth an extension of a flange or crest occurring along convex side of shaft and extending over curved tip or main tooth (Figs. 14E, 15E). Abdominal setigers from setiger 11 with parapodia as low ridges bearing setae arranged in long double rows almost entirely surrounding body; with dorsal, ventral, and lateral gaps approximating separate noto- and neuropodia; anterior row with about 12–15 acicular spines (Figs. 14F, 15D) per noto- or neuropodium; posterior row with numerous capillaries (Fig. 14F); acicular spines flattened, tapering to narrow tip (Figs. 14F, 15D); aristae not evident on any spines.

Posterior region a short rounded bulbous section, about as long as wide, distinctly set off from elongate abdominal segments by a groove (Figs. 14D, 15F); bearing four setigers each with a pair of curved hooks with pointed tips (Figs. 14G, 15E).

Methyl Green staining. No pattern.

Remarks. Heterospio alata n. sp. is the third of four species of the genus to be reported with neuropodial hooked spines on setiger 1. The first was H. catalinensis (Hartman, 1944) from southern California in shelf depths (Hartman 1944, 1957). The second species was Heterospio sp. A reported by Uebelacker (1984) from the Gulf of Mexico. The fourth is Heterospio bidentata n. sp. described from abyssal depths of eastern Australia (see below). Of these, H. catalinensis and H. sp. A have unidentate spines on setiger 1, whereas H. bidentata n. sp. and H. alata n. sp. both have bidentate spines. In H. bidentata n. sp. the apical tooth is a distinct secondary tooth arising directly from the shaft; whereas in H. alata n. sp. the apical “tooth” is an extension of a flange or crest that occurs along the convex side of the shaft and extends over the curved tip or main tooth of the hook providing the bidentate appearance. This type of hook is remarkably similar to the “ alate ” hooks found in some species the cirratulid genus Caulleriella (see Blake 2021b).

Other characters more or less limited to H. alata n. sp. include having only two pairs of branchiae on setigers 2–3, a single peristomial ring interrupted dorsally by a narrow dorsal crest, and the shift to cincture-like rows of noto- and neurosetae including acicular spines not occurring until setiger 11 rather than the more typical setiger 10.

Biology. Heterospio alata n. sp. was relatively rare throughout the two survey sites. Most of the specimens occurred at the CA1 survey site at Stations 46, 48, and 55 in sediment having 99% fine sediments (silt + clay) with the following grain size and TOC results by percent: Sta. 46: sand (1%), silt (79%), clay (20%), TOC (1%); Sta. 48: sand (4%), silt (73%), clay (26%), TOC (4%); Sta. 55: sand (1%), silt (52%), clay (47%), TOC (4.7%). One specimen (MCZ 163708) had eggs measuring 122–152 µm in diameter.

Etymology. The epithet alata is from the Latin alatus for wing, in reference to the apical tooth on the neuropodial hooks of setiger 1 that appears as an extension of a flange that occurs along the convex side of the shaft on the hook.

Distribution. South China Sea, off Brunei, Island of Borneo, 1114–1453 m.