Hydroides diramphus Mörch, 1863

Sun, Yanan, Ten, Harry A. & Qiu, Jian-Wen, 2012, Serpulidae (Annelida: Polychaeta) from Hong Kong, Zootaxa 3424, pp. 1-42 : 7-11

Hydroides diramphus Mörch, 1863

( Figure 2A , Figure 5 A–I)

Hydroides (Eucarphus) dirampha Mörch, 1863: 379 .

Hydroides lunulifera — Day 1967: 807.

Hydroides dirampha —Huang and Mak 1982: 780; Mak 1982: 600, 602; Morton and Morton 1983: 278; Wang and Huang 1993: 1 –12.

Hydroides diramphus —Bastida-Zavala and ten Hove 2003: 83–86; Ben-Eliahu and ten Hove 2011: 17 –19.

Material examined. AM W40539, 10 specimens (22°25’N, 114°16’E, Tolo Harbour, on the submerged side of the floating Styrofoam boxes in the fish farm, 3–10 m, April 15, 2009); AM W41404, 3 specimens (22°17’N, 114°11’E, Victoria Harbour, on pier concrete columns, 0–1 m, May 20, 2009).

Description. TUBE: white, circular in cross-section; longitudinal ridges, if present, very low, collar-like rings absent. Transversal ridges present throughout the whole tube. External tube diameter from 1.4 mm to 2.6 mm (n=8, µ=1.9±0.4), lumen diameter from 1.1 mm to 2.0 mm (n=8, µ=1.5±0.3).

BRANCHIAE: radioles on each side arranged in semicircle, numbers ranging from 14 to 18 (n=8, µ=15.6±1.6). Interradiolar membrane absent. Terminal filament long.

PEDUNCLE: smooth, circular in cross-section, inserted below left branchial lobe in 12 specimens, right in 1 specimen. Constriction well-defined. Pseudoperculum club-shaped with an inflated tip, present in all specimens.

OPERCULUM: funnel radii with pointed tip, numbers ranging from 30 to 42 (n=8 µ=35.5±5.6). Interradial grooves almost 3/4 of funnel length. Verticil with 12 to 18 yellowish spines (n=8, µ=14.3±3.2), straight, all spines similar in size and shape. Tip of spines T-shaped and flattened ( Figure 5 A), each having a basal internal spinule. External and lateral spinules absent. Central tooth absent. Length of operculum from 0.8 mm to 1.8 mm (n=8, µ=1.1±0.4), width from 1.1 mm to 1.8 mm (n=8, µ=1.3±0.3).

COLLAR AND THORACIC MEMBRANES: collar high, continuous with well-developed thoracic membranes.

THORAX: with 7 chaetigers, 6 uncinigerous. Collar chaetae of two types: bayonet chaetae with two long pointed teeth and smooth distal blade ( Figure 5 B), and capillaries with minute denticles ( Figure 5 C). Subsequent chaetae of two sizes (limbate and capillary, Figure 5 D). Uncini along entire thorax saw-shaped with 7 curved teeth including anterior fang ( Figure 5 E). Tori of similar size throughout, approaching each other posteriorly, leaving a ventral depression.

ABDOMEN: total number of abdominal chaetigers varies from 64 to 103 (n=8, µ=85.3±12.9). Uncini sawshaped throughout with fang and 4 teeth anteriorly, increasing to 8 to 9 teeth (incl. fang) posteriorly ( Figure 5 F–H). Chaetae flat trumpet-shaped ( Figure 5 I). Capillaries present posteriorly, glandular pad absent.

SIZE: total worm length: 12.0 mm to 32.0 mm (n=8, µ =19.4±8.2), thoracic width: 1.2 mm to 2.0 mm (n=8, µ=1.6±0.5). Branchiae and operculum accounting for one fifth of entire length.

COLOUR: yellow to light brown.

Habitat. Depth: 1–10 m, on pier piles or other artificial substrate, fouling.

Distribution. Circum(sub)tropical.

Remarks. Hydroides diramphus has been reported as a fouling species, being ship-transported easily (Bastida- Zavala & ten Hove 2003) and present in both polluted and non polluted areas ( Bastida-Zavala 2008). In Hong Kong, Hydroides diramphus occasionally occurs in the fouling community of local fish farms, co-occurring with Hydroides sanctaecrucis and Hydroides elegans on various submerged surfaces, with the latter species being dominant.

Figures

FIGURE 5. Hydroides diramphus, AM W 40539. A, operculum. B, bayonet collar chaetae. C, detail of denticulate capillary collar chaeta. D, thoracic limbate and capillary chaetae. E, uncini from chaetiger 7. 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 – C = 30 μm, D – H = 20 μm, I = 10 μm)

FIGURE 2. A, Hydroides diramphus, AM W 40539, lateral view, removed from tube. B, Hydroides elegans, AM W 40540, showing the operculum and branchial crown. C – D, Protula bispiralis, associated with living corals, showing the branchial crown. E, Spirobranchus kraussii, AM W 41410, operculum, lateral view, removed from tube. F. Spirobranchus tetraceros, associated with Porites lutea, showing the opercula and branchial crowns.