Paratherochaeta antoni ( Kirkegaard, 1996 ), 2013

Salazar-Vallejo, Sergio I., 2013, Revision of Therochaeta Chamberlin, 1919 (Polychaeta: Flabelligeridae), Zoosystema 35 (2), pp. 227-263 : 246-248

Paratherochaeta antoni ( Kirkegaard, 1996) n. comb.

( Fig. 7 )

Therochaeta antoni Kirkegaard, 1996: 64-66 fig. 5.

TYPE MATERIAL. — Indian Ocean , Bay of Bengal. Holotype of T. antoni ( ZMC 852 ), R/V Galathea, Stat. 311 (20°49’N, 88°40’E), off Ganges, India, 445 m, 2.V.1951.

ADDITIONAL MATERIAL. — Indian Ocean, Arabian Sea . One specimen ( LACM-AHF 5320), collected during the International Indian Ocean Expedition, R/V Anton Bruun, Arabian Sea, Stat. AB 247B (25º06’N, 60º45’E), 110 m, 28.XI.1963 (13.5 (8.5+5.5) mm long, 2 mm wide, cephalic cage 6 mm long, 34 (16+18) chaetigers; first neurohooks from chaetiger 8; gonopodial papillae small, dark, low rounded lobes, in chaetiger 5) .

DISTRIBUTION. — Northeastern Indian Ocean, in shelf depths (110-445 m).

DESCRIPTION

Holotype complete ( Fig. 7A ), slightly damaged, median region macerated, several parapodia with broken chaetae. Body subcylindrical, tapered anteriorly and posteriorly, swollen medially; 26 mm long, 2 mm wide, cephalic cage chaetae 17 mm long, 62 chaetigers.Tunic thin throughout the body. Body papillae variously covered by fine sediment particles; chaetigers 1-7 with sediment particles forming a thin, smooth crust along chaetigers 1-3, chaetigers 4-7 with sediment grains more irregularly placed covering large, subconical papillae ( Fig. 7B ); posterior chaetigers with individual papillae with very fine sediment particles, not blocking their individual shape. Chaetigers 3-7 with triangular sediment tubercles, larger in chaetigers 3-4, gradually decreasing in subsequently.

Cephalic tube exposed, made by two muscular rings ( Fig. 7C, D ); basal ring slightly wider, about as long as distal one; margin papillated. Anterior end exposed, heavily contracted, showing about 20 thin branchial filaments left, several branchial scars over lateral folds ( Fig. 7D ). Prostomium not seen. Palps lost. Dorsal lip short, lateral lips thicker; ventral lip reduced ( Fig. 7E ). Branchiae cirriform, sessile on branchial plate, arranged in two lateral groups (or spiraling rows), about 20 filaments per side. Nephridial lobes not seen.

Cephalic cage chaetae about as long as 7/10 body length, or more than ten times longer than body width. Chaetigers 1-2 involved in the cephalic cage; chaetiger 3 with long chaetae but not reaching the anterior margin of chaetiger 1. Cephalic cage chaetae arranged in short transverse rows over the body corners, four chaetae per bundle but chaetiger 1 with thicker, 2.5 times longer. Anterior dorsal margin of first chaetiger with long, blunt, rounded projection, margin finely papillated (two other ventrolateral similar, shorter, thinner lobes). Chaetigers 1-2 depressed, long papillae restricted to base of chaetal lobes. Chaetiger 1 very short, chaetiger 2 markedly longer, barely constricted towards its posterior margin, chaetiger 3 shorter, slightly wider than chaetiger 2, shorter than chaetiger 1.

Anterior shield surrounding chaetigers 1-3, smooth, in following chaetigers less well-defined,rough.Chaetal transition from cephalic cage to body chaetae abrupt; neurohooks start in chaetiger 6. Gonopodial lobes in chaetiger 5, sediment cover eroded, each rounded, short, slightly darker than sediment shield ( Fig. 7F ).

Parapodia well-developed in chaetigers 1-3, flat lobes with long papillae; remaining parapodia poorly developed, chaetae emerge from the body wall. Parapodia lateral, median neuropodia ventrolateral. Noto- and neuropodia short lobes, notopodia with a longer, capitate papillae; a single, smaller capitate interramal papillae. Noto- and neuropodia close to each other.

Median notochaetae arranged in short transverse series; all notochaetae multiarticulated capillaries, all articles long (longest articles three times longer than wide), progressively slightly smaller distally; two-three per bundle, 1/8-1/10 as long as body width, longer in posterior chaetigers. Neurochaetae multiarticulated capillaries in chaetigers 1-5 (seven in additional specimen), chaetiger 6 (eight in LACM-AHF 5320) with falcate simple neurospines, four-five per ramus in median and posterior chaetigers ( Fig. 7G ).

Posterior end tapered; pygidium rounded, colorless, with anus terminal, without anal cirri.

REMARKS

Therochaeta antoni Kirkegaard, 1996 does not belong in Therochaeta as it lacks pseudocompound neurochaetae in anterior chaetigers; it rather belongs in Paratherochaeta n. gen., and hence the new combination. It was described as having neurohooks in chaetiger 6, but the neuropodia had been previously removed, and the left side ones have no chaetae left, but since the anterior parapodia are well preserved, the original statement is regarded as correct. The additional specimen was found in shallower depths and is smaller in size, have neurohooks from chaetiger 8, but they are regarded as conspecific.

Paratherocaheta antoni ( Kirkegaard, 1996) n. comb. resembles P. coronata n. comb. They especially differ because they have a different relative size of articles in median and posterior notochaetae, and their neurohooks are different as well. Thus, in P. antoni the longest articles are about three times longer than wide and neurohooks are more delicate or thinner, whereas in P. coronata n. comb. they are 5-6 times longer than wide, and neurohooks are more robust and falcate. An additional difference refers to the depth where they occur since P. antoni lives in 110-445 m, and P. coronata n. comb. was found in about 1300 m depth.

Figures

FIG. 7. — Paratherochaeta antoni (Kirkegaard, 1996) n. comb., holotype (ZMC 852); A, dorsal view, anterior end exposed; B, anterior end, lateral view; C, anterior end, dorsal view; D, anterior end, ventral view; E, head, oblique frontal view; F, chaetigers 3-6, ventral view, arrows point gonopodial lobes; G, posterior chaetiger, right parapodium. Abbreviations: Br, branchiae, LL, lateral lip, PS, palp scar. Scale bars: A, 2 mm; B, 0.8 mm; C, 1.2 mm; D, 1.6 mm; E, 0.35 mm; F, 0.45 mm; G, 150 µm.