Pectinaria torquata, Zhang, Jinghuai & Qiu, Jian-Wen, 2017

Zhang, Jinghuai & Qiu, Jian-Wen, 2017, A new species of Pectinaria (Annelida, Pectinariidae), with a key to pectinariids from the South China Sea, ZooKeys 683, pp. 139-150 : 140

Pectinaria torquata sp. n. Figs 1, 2, 3

Material examined.

All type specimens are deposited in the Marine Biological Museum (MBM), Institute of Oceanology, Chinese Academy of Sciences, Qingdao

Holotype.

MBM240082: complete specimen, 22°45.17'N, 114°42.98'E (Daya Bay, Guangdong Province), 9.0 m water depth, muddy sand, August 2015.

Paratypes.

MBM240083: complete specimen, 22°35.50'N, 114°33.22'E (Daya Bay, Guangdong Province), 11.0 m water depth, muddy sand, June 2015. MBM240084: incomplete specimen with 17 anterior segments, 21°39.42'N, 108°34.46'E (Beibu Gulf, Guangxi Province), 9.7 m water depth, muddy sand, August 2015.

Etymology.

The specific epithet torquata is a Latin adjective for collar, which refers to the elevated collar-like dorsal posterior lobe on segment 2, a distinctive feature for this species.

Diagnosis.

Opercular margin smooth. Cephalic veil free from operculum, with 26-38 cirri along the rim. Segments 2 and 20 with a dorsal posterior lobe respectively. Body with 16 chaetigers. Neurochaetal uncini with major teeth arranged in two rows. Scaphe formed by fusion of five posterior segments. Four or five pairs of scaphal hooks.

Description of holotype.

Preserved specimen pale cream in color. Body stout with cephalic region enlarged (Figs 1A, 3 A–B). Body length 38.5 mm including scaphe, width 9.0 mm at cephalic region. Tube straight, conical, composed of cemented sand grains and shell fragments (Fig. 3C).

Opercular margin raised with smooth edge (Figs 1 A–B, 2A, 3 A–B). Cephalic veil free from operculum on dorsal side, with 26 cirri distributed along the rim (Figs 1 A–B, 2 A–B). Operculum with two bundles of paleae, each bundle with 12 stout, flattened, golden bristles curved dorsally and tapering to pointed tip (Figs 1 A–B, 2 A–B, 3 A–B).

Segment 1 with pair of tentacular cirri arising from antero–ventral edge near outer most paleae. Segment 2 with pair of tentacular cirri arising from both sides; tentacular cirri connected by flattened ridge running across venter (Figs 1B, 2 A–C), and dorsal posterior lobe running across both sides and dorsum (Figs 1B, 2A, 3A, 3G). Segments 3 with pair of comb-like lateral branchiae, and a median ventral lobe (Figs 1 A– 2, 2B, 3B). Segments 4 with pair of comb-like lateral branchiae which are smaller than the branchiae on segment 3, a small medial ventral lobe and two large ventral lateral lobes. Segment 5 with a small medial lobe and two large lateral lobes. Segment 6-9 also with pair of ventral lateral lobes but the size gradually decreased posteriorly. Segment 10 and posterior segments without ventral lateral lobes (Figs 1A, 2A, B). Segment 20 with dorsal posterior lobe.

Chaetigers 1-3 (segments 5-7) uniramous with pair of wedge-shaped notopodia only (Fig. 1 A–B). Chaetigers 4-16 (segments 8-20) biramous with pair of wedge-shaped notopodia and pair of ear-shaped neuropodia (Fig. 1 A–D). Segment 21 with a dorsal posterior lobe and pair of lateral lobes, but without chaetae (Figs 1 C–D, 3 H–I).

Notopodia with two kinds of capillaries forming bundle: both with finely hirsute surface on anteromedian margin and smooth surface on posterior margin; one kind with serrations along anterior portion of tip; the other kind smooth, tapering to very acute tip (Figs 1 G–H, 2 D–J). Neuropodia with uncini arranged in row along the ridge, each uncinus with major teeth arranged in two rows, 7-8 teeth per row (Figs 1E, 2K).

Scaphe distinctly separated from segment 21 (Figs 1A, 3 A–B), formed by fusion of five posterior segments. Scaphe longer than broad, arched ventrally and flattened dorsally with crenulated lateral margin (Figs 1 B–C, 3D, H–I). Anal flap tongue-shaped with tip extending beyond posterior scaphal edge; anal flap margin crenulated (Figs 1D, 3 D–E). Scaphal hooks short, barely visible, with a curved blunt tip; five on right and four on left; present in the dorsolateral region of scaphe, approximately half way between the junction with segment 21 and the posterior edge (Figs 1F, C–D, 3F, I).

Variation.

Comparison among the types shows that the body width in the cephalic region varies from 8 to 10 mm. The number of paleae varies from 11 to 12 pairs. The number of cirri on the cephalic veil margin varies from 26 to 32. The number of scaphal hooks varies from 4 to 5 pairs. Since there are only two complete and one incomplete specimens of similar sizes, intraspecific variation amongst these morphological characters may have been underestimated.

Type locality and distribution.

Currently only known from Daya Bay (Guangdong Province) and Beibu Gulf (Guangxi Province) in the northern South China Sea.

Remarks.

Pectinaria torquata sp. n. can be distinguished from the other 25 described species of Pectinaria by several features (Table 1). First, it has a dorsal posterior lobe on segment 2, which is unique among the described species of Pectinaria species. This structure is prominent in the type specimens, and does not change by preservation. Second, P. torquata sp. n. has a dorsal posterior lobe on both segment 20 and 21, a feature that has not been reported from any other recognized species in this genus ( Hartman 1941, Long 1973, Hutchings and Peart 2002, Nishi et al. 2014, Wong and Hutchings 2015). Third, P. torquata sp. n. has only 4-5 pairs of small blunt scaphal hooks, which is fewer than those in most described species. Fourth, the anal flap lacks a middorsal anal cirrus with a crenulated margin. There are eight species in which the dorsal posterior lobe on segment 2 is not recorded (Table 1). Except for Pectinaria dimai Zachs, 1933 and Pectinaria panava Willey, 1905 for which the middosal anal cirrus is not described, the other five species have a middorsal anal cirrus; P. torquata sp. n. lacks a middorsal anal cirrus (Table 1). Furthermore, it differs from P. dimai which has 3-4 rows of major teeth on each uncinus, and 6-7 teeth per row; P. torquata sp. n. has 2 rows of major teeth, and 7-8 teeth per row. Pectinaria panava has more scaphal hooks than P. torquata sp. n.

A key to eleven species of Pectinariidae , including P. torquata sp. n., that have been recorded from the South China Sea in the literature is provided below ( Wu and Chen 1985, Yang and Sun 1988, Paxton and Chou 2000, Sun and Qiu 2012, Salazar-Vallejo et al. 2014, Zhang et al. 2015, Glasby et al. 2016). The genera Petta and Cistenides have not been recorded in the South China Sea.