Hydroides albiceps ( Grube, 1870 )

Sun, Yanan, Ten, Harry A. & Qiu, Jian-Wen, 2012, Serpulidae (Annelida: Polychaeta) from Hong Kong, Zootaxa 3424, pp. 1-42 : 7

Hydroides albiceps ( Grube, 1870)

( Figure 3A–B , Figure 4 A–H)

Serpula (Eupomatus) albiceps Grube, 1870: 520 –521.

Hydroides albiceps — Fauvel 1953: 460; Imajima 1976a: 133 –135; Mak 1982: 601–602; Imajima and ten Hove 1984: 43 –44; Yang and Sun 1988: 311; Wang and Huang 1993: 1 –12; Fiege and Sun 1999: 112 –114.

Material examined. AM W40534, 11 specimens (22°21’N, 114°17’E, Sharp Island, on dead coral, 3–6 m, May 21, 2009).

Description. TUBE: white, with two longitudinal ridges. Subtrapezoid in cross-section. Medial keel absent. External tube diameter from 1.0 mm to 1.6 mm (n=5, µ=1.3±0.3), lumen diameter from 0.6 mm to 1.2 mm (n=5, µ=0.9±0.2).

BRANCHIAE: radioles on each side arranged in semicircle, numbers ranging from 7 to 12 (n=6, µ =10±1.8), terminal filaments long. Interradiolar membrane absent.

PEDUNCLE: smooth, circular in cross-section, inserted just below left branchial lobe (n=3). Constriction hardly visible. Pseudoperculum club-shaped, present in all specimens.

OPERCULUM: funnel light yellowish, bearing conical radii with blunt and slightly chitinized tip, numbers of radii ranging from 12 to 24 (n=9,µ=20.4±3.1) ( Figure 3A–B ). Verticil milky white basally, yellowish marginally, consisting of one large vesicular spine with a dorsolateral extension on each side of its tip, and eight smaller, subequal conical spines with blunt, outward curving tip ( Figure 3A–B ). Interradial grooves almost 3/4 of funnel length. Lateral and internal spinules absent. Central tooth absent. Three specimens with two opercula each. Operculum length from 0.5 mm to 1.0 mm (n=9, µ=0.7±10.2), width from 0.5 mm to 1.0 mm (n=9, µ=1.6±0.2).

COLLAR AND THORACIC MEMBRANES: collar high, with entire edge.

THORAX: with 7 chaetigers, 6 uncinigerous. Collar chaetae of two types: bayonet-type with two conical teeth at the base of a finely striated blade and finely striated capillaries ( Figures 4 A–B). Subsequent chaetae of two sizes (limbate and capillary, Figure 4 C). Uncini along entire thorax saw-shaped, with 7 to 8 curved teeth including anterior fang ( Figure 4 D). Tori of similar size throughout.

ABDOMEN: total number of abdominal chaetigers varies from 63 to 80 (n=3, µ=72.3±12). Uncini saw-shaped anteriorly, with fang and 5 to 6 teeth ( Figure 4 E–F); rasp-shaped with 2 to 4 rows of teeth, fang and 8 to 9 teeth in profile view posteriorly ( Figure 4 G–H). Chaetae flat trumpet-shaped. Capillaries present posteriorly, glandular pad absent.

SIZE: total worm length: 11.4 mm to 20.0 mm (n=3, µ=15.6±6.1), width of thorax: 0.5 mm to 1.0 mm (n=6, µ=0.7±0.1). Branchiae and operculum accounting for one fifth of entire length.

COLOUR: in ethanol pale white or yellowish.

Habitat. Depth, 3–6 m, on dead corals.

Distribution. Widely distributed in tropical and subtropical waters of the Indian Ocean and Pacific Ocean.

Remarks. The opercula of Hydroides albiceps show a large variability in morphology. The tips of the radii and verticil spines may range from blunt (our specimens from Hong Kong) to laterally dilated as mentioned in the literature, e.g. in the holotype. It remains to be studied if such differences are ontogenetic, or if there is a geographical component to these variations.

Figures

FIGURE 4. Hydroides albiceps, AM W 40534. A, bayonet collar chaetae. B, detail of distal tip of bayonet collar chaeta. C, thoracic limbate chaetae. D, uncini from chaetiger 4. E, anterior abdominal uncini. F, middle abdominal uncini. G, H, posterior abdominal uncini. (Scale bars: A – F = 10 μm)

FIGURE 3. A – B: Hydroides albiceps, AM W 40534, operculum, lateral and apical view. C: Hydroides operculatus, AM W 41406, operculum, lateral view. D – J: Hydroides rhombobulus, AM W 41407. D – E, operculum, lateral and apical view. F, G, collar chaetae. H, thoracic limbate chaeta. I, thoracic uncinus. J, abdominal uncinus. K – O: Protula bispiralis, AM W 41409. K, dorsal view; L, limbate collar chaeta. M, limbate chaeta from chaetiger 6. N, abdominal sickle-shaped chaeta. O; abdominal uncinus. P – Q: Serpula cf. granulosa, AM W 40554, operculum, lateral and apical view. (Scale bars: A – E = 0.2 mm, F – G, O = 50 μm, I – J = 10 μm, K = 5 mm, L – N = 100 μm, P – Q = 1 mm)