Spirobranchus

Sun, Yanan, Ten, Harry A. & Qiu, Jian-Wen, 2012, Serpulidae (Annelida: Polychaeta) from Hong Kong, Zootaxa 3424, pp. 1-42 : 35-37

Spirobranchus sp. B

( Figure 14 K, Figure 17 A–E)

Material examined. AM W41414, 4 specimens (22°21’N, 114°17’E, Sharp Island, on dead coral, 3–6 m, May 21, 2009).

Description. TUBE: missing.

BRANCHIAE: radioles arranged in a circle on each lobe, numbers ranging from 9 to 10 (n=3, µ=9.7±0.6), interradiolar membranes extending to about half of radiolar length, without marginal fringes. Terminal filament thin and long, approximately 0.4 mm. Branchial eyes not observed.

PEDUNCLE: smooth, flat in cross-section. Pair of triangular lateral wings, fringed along anterior margin, with 4–6 short processes.

OPERCULUM: Opercular plate conical, consisting of 8–10 transverse annuli with numerous small projections on surface of each annulus; topmost disc slightly concave, with a small convex projection ( Figure 14 K). Length of the operculum from 2.8 mm to 3.4 mm (n=3, µ=3.1±0.3), widths from 0.9 mm to 1.1 mm (n=3, 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 bayonet-like, with striated blade and numerous small teeth forming squarish emboss at base of blade ( Figure 17 A). Subsequent chaetae of two sizes, limbate (Figure 17B) and capillary. Uncini saw-shaped, with 9–10 teeth in a single row and gouged peg ( Figure 17 C). Tori increasing in length along thorax, approaching each other posteriorly, leaving a ventral depression.

ABDOMEN: total number of abdominal chaetigers varies from 65 to 76 (n=2, µ=70.5±7.8). Uncini sawshaped, with 7 to 8 teeth in a row anteriorly ( Figure 17 D), increasing to 13 to 14 teeth in a row in middle abdomen and posteriorly. Chaetae true trumpet-shaped, abruptly bent distally, with two rows of denticles separated by a hollow groove and forming long lateral spine ( Figure 17 E).

SIZE: total worm length: 10.6 mm to 17.8 mm (n=2, µ =14.2±5.1), thoracic width: 1.0 mm to 1.1 mm (n=3, µ=1.0±0.1).

COLOUR: in ethanol operculum light brown, peduncle and wings light blue with dark blue pigmentation, branchial radioles purplish blue proximally and light blue distally, collar blue, thorax and abdomen yellowish.

Habitat. Depth: 3–6 m, on dead coral skeleton.

Remarks. Spirobranchus sp. B is similar to S. acuiconus described by Pillai (2009) in having an annulated calcareous operculum. However, the operculum of S. acuiconus bears more annuli than our specimens (13 vs. 8–10). Moreover, projections arising from operculum plates, observed in our specimens, are absent in S. acuiconus . Alternatively, the light brown colour of the operculum and the fringed peduncular wings indicate its similarity with S. tetraceros , as with the previous sp. A it might fall in the range of variability as described for this taxon as defined by Ben-Eliahu and ten Hove (2011 fig.33). In view of the uncertainties within the S. tetraceros -complex we prefer to describe the material fully, but not to assign this material to a definite name.

Figures

FIGURE 17. Spirobranchus sp. B. AM W 41414. A, bayonet-like collar chaetae. B, limbate chaetae from chaetiger 4. C, uncini from chaetiger 4. D, anterior abdominal uncini. E, abdominal trumpet-shapedi chaeta. (Scale bars: A – B = 20 μm, C – E = 10 μm)

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)