Spirobranchus incrassatus Krøyer, 1863

Bastida-Zavala, J. Rolando, 2008, Serpulids (Annelida: Polychaeta) from the Eastern Pacific, including a brief mention of Hawaiian serpulids, Zootaxa 1722, pp. 1-61 : 49

Spirobranchus incrassatus Krøyer [in] Mörch, 1863

( Figures 12C–E)

Spirobranchus incrassatus Krøyer [in] Mörch, 1863: 405, pl. 11, figs. 21–23. Type locality: Western Colombia. Spirobranchus incrassatus .— Ehlers, 1887: 294–295, pl. 57, fig. 16, pl. 58, figs. 1–5, Acapulco (Guerrero, Mexico). Spirobranchus giganteus .— Bastida-Zavala, 1995: 26–26, Cabo Pulmo Reef (Baja California Sur, Mexico). Spirobranchus giganteus giganteus .— ten Hove, 1970: 16–17, 20–22, 49, figs. 46–47 (synonym of S. incrassatus Krøyer

[in] Mörch, 1863).

Material examined. Sixty-three specimens: Baja California Sur ( Mexico), UMAR-Poly 99, 7 spec. (23º24– 25’N, 109º25’W, Cabo Pulmo Reef, Coral Los Frailes and third bar, on dead coral Pocillopora , 4–17 m, Sept. 25, 1988 and Sept. 18, 1989, coll. PH, JK & JRBZ, as S. giganteus ); ECOSUR s.n., UMAR-Poly 100, 12 spec. (approx. 26º00’51”N, 111º20’21”W, Loreto pier, in pier pilots, oysters, March 3, 2004, coll. MATH & PSS) . Sinaloa ( Mexico), ECOSUR s.n., UMAR-Poly 101, 2 spec. (approx. 23º14’N, 106º27’W, Isla Venados, Mazatlan, basaltic rocks, algae and sand, 2 m, Feb. 26, 2004, coll. MATH & PSS) . Colima ( Mexico), UANL 350 (approx. 19º03–06’N, 104º18–22'W, Manzanillo , Oct. 7, 1981, coll. S. Salcedo Martínez, as S. giganteus ) . Guerrero ( Mexico), SV-pc, 25+ spec. (16º50’33”N, 99º54’39”W, Punta Manzanillo , Acapulco, Aug. 4 and 20, 1988, coll. SISV); SV-pc, 6 spec. (16º51’26”N, 99º52’20”W, Condesa beach, Acapulco, Nov. 27, 1999, coll. SISV); UMAR-Poly 102, 9 spec. (16º50’N, 99º54’W, Cantiles and La Quebrada, Acapulco, on rock oysters and Pinctada , 8 m, May 25 and 26, 2000, coll. A. Medina) . Oaxaca ( Mexico), UMAR-Poly 103 (15º51’N, 97º04’W, Puerto Escondido, on Spondylus calcifer , M10, 6– 10 m, July 4, 2004, coll. SS) .

Diagnosis. Tube white, greyish or violet, sometimes covered with bryozoans or coralline algae, with prominent longitudinal ridge. Anteriormost section of tube forms robust spine extending over opening of tube, usually this spine and opening violet, pinkish or bluish in colour; lacking peristomes or alveoli. Opercular peduncle with wide wings. Operculum calcareous, circular or pear-shaped. Opercular surface bears three spines, emerging from dorsalmost part of opercular plate. Two latero-dorsal spines thin, with an additional 6– 10 spinules and one small and thin basal branch; the medio-ventral third spine widely bifurcated ( Figs 12C– D). Radioles arranged in spire of up to five whorls. Thoracic membrane extends to last thoracic chaetiger, forming short ventral apron. Collar with “ Spirobranchus ” chaetae, coarsely serrated in sub-apical section.

Measurements. TL=36.5 mm (n=9, r:14–36.5, µ=27.7 ±8.3), THL= 6 mm (n=10, r:3.5–6, µ=5.1 ±1.1), THW= 6 mm (n=10, r:2.5–6, µ=4.1 ±1.1), POL= 13 mm (n=10, r:6–13, µ=9 ±2.2), OL= 6 mm (n=10, r:2.5–6, µ=4.1 ±1.1), OW= 5 mm (n=10, r:2.3–5, µ=3.9 ±1), SL= 5 mm (n=10, r:2–5, µ=3.5 ±1).

Habitat. Depth: 6– 17 m. On live and dead coral ( P. verrucosa ), on spiny oyster Spondylus calcifer and Pinctada , and on pier pilots.

Distribution. Tropical Eastern Pacific. Baja California Sur ( Mexico) to Panama and Colombia (Krøyer [in] Mörch 1863; Ehlers 1887; ten Hove 1970; Bastida-Zavala 1995).

Taxonomic remarks. Ten Hove (1970) considered the population of S. incrassatus from the Eastern Tropical Pacific as a subspecies ( S. giganteus incrassatus ), since most of his specimens had opercula with slight differences to S. giganteus from the Caribbean Sea. Spirobranchus giganteus was a common name in the Eastern Pacific species checklists. With the material revised here (more than 60 specimens), from localities from Baja California Sur to Panama, Fiege and ten Hove’s (1999: 363) opinion that S. incrassatus is different from S. giganteus , can be confirmed because of the following:

1) All measurements of the specimens of Spirobranchus giganteus are greater those of S. incrassatus ; particularly in the ratio between thorax length and peduncle which separates the two species ( Fig. 12E).

2) The mid-ventral spine in S. incrassatus (present in 90% of the specimens) has a wide bifurcation (1/3 to 1/2 of the total length of the spine) and more additional spinules (6–8) in each lateral spine ( Fig. 12C); while in S. giganteus , whenever a mid-ventral spine is present (in less that 50% of the specimens), it exhibits short bifurcation (1/4 of the total length of the spine) and fewer additional spinules (0–5).