Hydroides exaltatus ( Marenzeller, 1885 )

Sun, Yanan, Ten, Harry A. & Qiu, Jian-Wen, 2012, Serpulidae (Annelida: Polychaeta) from Hong Kong, Zootaxa 3424, pp. 1-42 : 13-15

Hydroides exaltatus ( Marenzeller, 1885)

( Figure 7 A–I)

Eupomatus exaltatus Marenzeller, 1885: 217 .

Hydroides exaltata — Imajima 1976a: 127 –128; Mak 1982: 603; Imajima and ten Hove 1984: 48; 1986: 4–5; Sun and Yang 2000: 121; Fiege and Sun 1999: 116; Pillai 2009: 115 –116.

Material examined. AM W40542, 9 specimens (22°21’N, 114°17’E, Sharp Island, on dead coral, 3–6 m, May 21, 2009).

Description. TUBE: white, trapezoidal in cross-section, with two longitudinal ridges. Collar-like rings absent. External tube diameter: from 1.7 mm to 2.3 mm (n=3, µ=2.0±0.4), with lumen diameter from 1.3 mm to 1.7 mm (n=3, µ=1.4±0.2).

BRANCHIAE: each lobe with 10 to 15 radioles (n=5, µ=12.4±1.9) arranged in semicircle. Interradiolar membrane absent. Terminal filament long, about 1/5 of whole radiolar length.

PEDUNCLE: smooth, circular in cross-section, inserted below left branchial lobe. Constriction well-defined, chitinized. Pseudoperculum short, club-shaped.

OPERCULUM: numbers of radii ranging from 21 to 27(n=7, µ=24.4±2.2); tips yellowish, pointed, chitinized, curving outward. Interradial grooves 1/2 to 2/3 of funnel length. Verticil consisting of 7 to 9 spines (n=7, µ=7.7±1.1). The most dorsal one much larger, expanding upward before curving inward, tapering to a pointed tip, a slight depression present externally on each lateral side beneath expanded part. Remaining smaller spines similar in shape and size, all strongly curving outward, tapering to a pointed tip ( Figure 7 A). All spines with a small internal spinule arising from the base of spine. Central tooth absent. Opercular length from 0.8 mm to 2 mm (n=6, µ=1.4±0.5), width from 0.5 mm to 1.2 mm (n=6, µ=0.9±0.2).

COLLAR AND THORACIC MEMBRANES: collar high, thoracic membranes well-developed, apron present.

THORAX: with 7 chaetigers, 6 uncinigerous. Collar chaetae of two types: bayonet chaetae with two long pointed teeth and smooth distal blade, and capillaries with minute denticles ( Figure 7 B). Subsequent chaetae of two sizes (limbate and capillary, Figure 7 C–D). Uncini along entire thorax saw-shaped with 6–7 curved teeth including anterior fang ( Figure 7 E). Tori of similar size throughout.

ABDOMEN: total number of abdominal chaetigers varies from 52 to 59 (n=2, µ=55.5±4.9). Uncini sawshaped with 4 to 5 teeth anteriorly ( Figure 7 F), increasing to 6 to 7 in the middle ( Figure 7 G); rasp-shaped posteriorly with 2 to 3 rows of teeth and 7 to 8 teeth (incl. fang) in profile view ( Figure 7 H). Chaetae flat trumpet-shaped ( Figure 7 I). Capillary chaetae not observed. Posterior glandular pad absent.

SIZE: total worm length: 9.6 mm to 19.4 mm (n=5, µ=13.2±3.8), thoracic width: 0.9 mm to 1.2 mm (n=5, µ=1.1±0.1). Branchiae and operculum accounting for one fourth of entire length.

COLOUR: white.

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 collar capillaries of this species have been described differently: limbate ( Imajima 1976a), smooth ( Fiege & Sun 1999; this study), or without mentioning whether they are limbate or smooth (Mak 1982; Pillai 2009); this probably is rather a matter of quality of optics and of interpretation than of real differences. The present specimens agree with Imajima’s description. The position of the internal spinules has been reported to be on halfway of each spine ( Pillai 2009), in error, as his figures clearly depict a basal position.

Figures

FIGURE 7. Hydroides exaltatus, AM W 40542. A, operculum. B, collar chaetae. C, limbate and capillary chaetae from chaetiger 4. D, details of limbate chaetae from chaetiger 4. E, uncini from chaetiger 4. F, anterior abdominal uncini. G, middle abdominal uncini. H, posterior abdominal uncini. I, toothed edge of flat-trumpet chaetae from posterior abdomen. (Scale bars: A = 200 μm, B = 20 μm, C = 100 μm, D – I = 10 μm)