Chrysopetalum occidentale

(Figures 7 A – K, 8, 14 H, 15 E)

Description. Based mainly on the largest complete specimen, 3.1 mm long, 0.9 mm wide, 41 segments. Body broad and rectangular, pale orange to yellow, with reddish tones at the base of neuropodia. Paleae fan yellow to golden, interlocking over dorsum. Prostomium rounded and completely visible among the first two segments. Two lateral and subulate antennae; a wide median antenna inserted between first and second pair eyes. Two pairs of reddish eyes, first pair slightly bigger than second pair, in some specimens there is a central eyespot in front of first eyes pair. Nuchal fold smaller than prostomium. Two bilobe large palps. Small and semicircular mouth fold between third and fourth segment. Eversible proboscis with two slim stylets. Parapodium from the tenth segment. Notochaetae separated in three main groups and one subgroup (Fig. 7 A). Lateral group inserted just below notoaciculum; comprising 1 – 2 slender and spine-like paleae with 3 – 4 ribs and one raised rib (Fig. 7 F). As sub-unit 1, one asymmetrical palea with four ribs (Fig. 7 G). Main group, comprising 14 – 20 symmetrical paleae (the length of these paleae group is variably on all segments) with 5 – 8 ribs (Fig. 7 H). Median group, comprising 3 – 4 asymmetrical, small and curved paleae with 4 – 5 ribs and 0 – 1 raised rib, the most proximal palea is smaller than the distal palea with four ribs (Figs 7 I – K). Neuropodium slightly small, conical shaped. Heterogomph neurochaetae composed of four groups (Figs 7 B – E). Neurochaetiger with 1 – 2 superior spinigers with a partially curved and slightly serrated blade. In the first three segments neurochaetae spines and superior spinigers only. Mid-superior group consists of 4 – 6 falcigers, with blades as long as the superior spiniger blades. Mid-inferior group with 5 falcigers with medium length blades (3 / 4 of spiniger blade length) and serration basally. Inferior group with 2 – 3 falcigers, with short and smooth blade (1 / 4 of spiniger blade length). Pygidium rounded with two anal cirri. Habitat. Intertidal to subtidal (0.5 – 9.7 m). The revised specimens were mostly found on dead coral, bivalves and pier pilings. This species is usually associated with bryozoans, hydrozoans, tunicates, sponges and fouling fauna (Hartman 1961).

Remarks. Specimens from the southern Mexican Pacific agree with the redescription of Chrysopetalum occidentale by Perkins (1985), as well as with the description of specimens of C. occidentale from Panama by Aguado et al. (2003). The only difference among them was the number of paleae in the main group, decreasing in a latitudinal gradient. Californian specimens showed the highest number of paleae, 35 – 40 (Perkins 1985); specimens from northwest Mexico showed a maximum of 30 paleae (Perkins 1985); from southwest Mexico, specimens showed 14 – 20 paleae, while specimens from Coiba, Panama, showed 15 – 24 paleae (Aguado et al. 2003).

Distribution. California and Tropical Eastern Pacific, from northwest Mexico to Galapagos islands (Monro 1933; Rioja 1941; Hartman 1961; Gómez et al. 1997; Dean et al. 2012) (Fig. 8).

Material examined. Guerrero: UMAR-Poly 889, four spec. (La Ropa Beach, 17 ° 37 ’ 37 ’’ N, 101 ° 32 ’ 46 ’’ W, on rocks, 0.5 m, September 19, 2007, coll. M. S. García-Madrigal); UMAR-Poly 890, one spec. (Ixtapa Island, 17 ° 40 ’ 36 ’’ N, 101 ° 39 ’ 22 ’’ W, on rock, 1 m, September 19, 2007, coll. M. S García-Madrigal); UMAR-Poly 891, seven spec. (La Roqueta Island, Acapulco, 16 ° 49 ’ 21 ’’ N, 99 ° 54 ’ 29 ’’ W, 0 – 4 m, September 21, 2007, coll. M. S. García-Madrigal); UMAR-Poly 892, two spec. (Morro del Cerro Colorado, 17 ° 40 ’ 47 ’’ N, 101 ° 30 ’ 31 ’’ W, on stony coral, 2.7 – 4 m, November 30, 2010, coll. S. D. Güenduláin); UMAR-Poly 893, one spec. (Morros de Potosí, 17 ° 38 ’ 49 ’’ N, 101 ° 37 ’ 44 ’’ W, on stony coral, 6.1 – 11.7 m, December 3, 2010, coll. S. D. Güenduláin); UMAR-Poly 894, two spec. (Manzanillo Beach, 16 ° 50 ’ 31 ’’ N, 99 ° 54 ’ 37 ’’ W, on Pocillopora damicornis, 3 – 6.1 m December 4, 2010, coll. S. D. Güenduláin et al.); Oaxaca: UMAR-Poly 895, four spec. (El Arrocito Beach, 15 ° 45 ’ 38 ’’ N, 96 ° 06 ’ 00 ’’ W, on dead coral, 3 m, May 25, 2000, coll. J. R. Bastida-Zavala); UMAR-Poly 896, four spec. (Estacahuite Bay, 15 ° 40 ’ 05 ’’ N, 96 ° 28 ’ 56 ’’ W, on rocks, 3 m, April 9, 2005, coll. J. R. Bastida-Zavala); UMAR-Poly 897, five spec. (Estacahuite Bay, 15 ° 40 ’ 05 ’’ N, 96 ° 28 ’ 56 ’’ W, May 12, 2005); UMAR-Poly 898, one spec. (Panteón Beach, 15 ° 39 ’ 50 ’’ N, 96 ° 29 ’ 43 ’’ W, on P. damicornis, May 28, 2005); UMAR-Poly 899, one spec. (Estacahuite Bay, 15 ° 40 ’ 05 ’’ N, 96 ° 28 ’ 56 ’’ W, on dead coral, November 9, 2005, coll. M. S. García-Madrigal); UMAR-Poly 900, six spec. (Carrizalillo Beach, Puerto Escondido, 15 ° 85 ’ 95 ’’ N, 97 ° 07 ’ 87 ’’ W, on bivalves, August 12, 2006, coll. I. Gutiérrez & N. Pedroza); UMAR-Poly 901, fourteen spec. (Estacahuite Bay, 15 ° 40 ’ 05 ’’ N, 96 ° 28 ’ 56 ’’ W, on dead coral, 3 m, August 25, 2006, coll. J. R. Bastida-Zavala); UMAR-Poly 902, eleven spec. (La Tijera, 15 ° 41 ’ 14 ’’ N, 96 ° 26 ’ 34 ’’ W, on dead coral, September 12, 2006, coll. J. R. Bastida-Zavala); UMAR-Poly 903, one spec. (El Faro, Chacahua Lagoon, 15 ° 57 ’ 49 ’’ N, 97 ° 40 ’ 35 ’’ W, April 13, 2007, coll. M. S. García-Madrigal); UMAR-Poly 904, one spec. (main pier, Puerto Ángel, 15 ° 39 ’ 55 ’’ N, 96 ° 29 ’ 28 ’’ W, on pier pilings, 0.5 m, May 20, 2007, coll. F. Cortés- Carrasco); UMAR-Poly 905, four spec. (El Arrocito Beach, 15 ° 45 ’ 38 ’’ N, 96 ° 06 ’ 00 ’’ W, on dead coral, 3 m, July 4, 2007, coll. B. Martínez); UMAR-Poly 906, two spec. (Chacahua Lagoon, 15 ° 58 ’ 07 ’’ N, 97 ° 41 ’ 01 ’’ W, on sabellariid aggregation, 0.5 m, April 3, 2008, coll. P. Hernández); UMAR-Poly 907, three spec. (La Tijera, 15 ° 41 ’ 14 ’’ N, 96 ° 26 ’ 34 ’’ W, on dead coral, 3 m, April 7, 2009, coll. F. Cortés-Carrasco); UMAR-Poly 908, one spec. (Montosa Island, 15 ° 45 ’ 52 ’’ N, 96 ° 05 ’ 04 ’’ W, on P. damicornis, 2.7 – 5.8 m, February 22, 2010, coll. R. Granja-Fernández & S. D. Güenduláin); UMAR-Poly 909, one spec. (Estacahuite Bay, 15 ° 40 ’ 05 ’’ N, 96 ° 28 ’ 56 ’’ W, on P. damicornis, 6.4 – 9.7 m, March 26, 2010, coll. A. López-Pérez & R. Zepeta); UMAR-Poly 910, four spec. (Mazunte, 15 ° 39 ’ 42 ’’ N, 96 ° 33 ’ 21 ’’ W, on P. damicornis, 7.5 m, August 11, 2010, coll. A. López-Pérez).