Spirobranchus

Sun, Yanan, Ten, Harry A. & Qiu, Jian-Wen, 2012, Serpulidae (Annelida: Polychaeta) from Hong Kong, Zootaxa 3424, pp. 1-42 : 34-35

Spirobranchus sp. A

( Figure 14 F–J)

Material examined. AM W41413, 2 specimens (22°21’N, 114°17’E, Sharp Island, on dead coral, 3 m, May 21, 2009).

Description. TUBES: white, with two almost medial longitudinal ridges, and a series of pits along both sides of these ridges. Subtriangular in cross-section. Up to 1.1 mm wide with lumen 0.7 mm.

BRANCHIAE: radioles arranged in a circle on each lobe, numbers ranging from 10 to 13 (n=2, µ=11.5±2.1); interradiolar membranes extending to about half of radiolar length, fringed between radioles. Pinnules and terminal filament thin and long. Branchial eyes not observed.

PEDUNCLE: smooth, flat in cross-section, inserted just below right branchial lobe. Pair of lateral wings present, fringed with 4–6 digitiform processes along anterior margin.

OPERCULUM: opercular plate conical, with 4 to 5 indistinct annuli, one horn with two broken off spines arising from apex of plate ( Figure 14 F). Opercular length from 2.9 mm to 3.5 mm (n=2, µ=3.2±0.4), width from 0.9 mm to 1.1 mm (n=2, µ=1.0±0.1).

COLLAR AND THORACIC MEMBRANES: collar high, trilobed, continuous with well-developed thoracic membranes, forming apron across anterior abdominal chaetigers.

THORAX: with 7 chaetigers, 6 uncinigerous. Collar chaetae of two types: bayonet-like with striated blade and numerous small teeth forming squarish emboss at base of blade ( Figure 14 J) and slender, almost smooth capillaries. Subsequent chaetae of two sizes, limbate ( Figure 14 H) and capillary. Uncini saw-shaped, with 10-12 teeth in a single row and gouged peg ( Figure 14 G). Tori increasing in length along thorax, approaching each other posteriorly, leaving a ventral depression.

ABDOMEN: abdominal chaetigers 49. Uncini saw-shaped, with peg and 9 to 10 teeth in a row anteriorly (Figure 14J), increasing to 13 to 14 teeth in a row in middle and posterior abdomen. Chaetae true trumpet-shaped, with asymmetrical distal ends.

SIZE: incomplete specimens, length up to 7 mm, width of thorax 0.7 mm.

COLOUR: in ethanol operculum blue posteriorly and light brown anteriorly, peduncle and wings light blue with darker blue spots, branchial radioles banded alternatingly blue and white, thorax and anterior abdomen blue, posterior abdomen colourless.

Habitat. Depth: 3 m, on dead coral skeleton.

Remarks. Spirobranchus sp. A most probably belongs to the S. tetraceros -complex (Ben-Eliahu & ten Hove 2011: 91, fig.33). It is similar to S. elatensis described by Pillai (2009) in having a conical operculum with a brown apex. However, these two species differ in the morphology of their tubes: that of S. elatensis does not show series of pits and has three longitudinal ridges ( Pillai 2009) while that of Spirobranchus sp. A has numerous pits and two longitudinal ridges only. Since Ben-Eliahu and ten Hove (2011: 91) consider S. elatensis to be a synonym of S. tetraceros , however, the tubes of the two specimens under consideration here differ by the rows of pits along the medial keels from the tubes of our S. tetraceros , we prefer to describe the material fully, but not to assign this material to a definite name.

Figures

FIGURE 14. A – C: Spirobranchus cf. polytrema type A, AM W 41412. A, tube. B – C, operculum, lateral and apical view. D – E: Spirobranchus tetraceros, AM W 41411, operculum, lateral and apical view. F – J: Spirobranchus sp. A, AM W 41413. F, operculum, lateral view. G, bayonet-like collar chaeta. H, thoracic chaetaa. I, thoracic uncinus. J, anterior abdominal uncinus. K: Spirobranchus sp. B, AM W 41414, operculum, lateral view. L: Vermiliopsis glandigerus, AM W 41415, operculum, lateral view. (Scale bars: A, D – E = 1 mm, B – C, F = 0.5 mm, G – H = 100 μm, I – J = 20 μm, K – L = 0.2 mm)