Alpheus arenensis ( Chace, 1937 )

Anker, Arthur, Hurt, Carla & Knowlton, Nancy, 2008, Revision of the Alpheus websteri Kingsley, 1880 species complex (Crustacea: Decapoda: Alpheidae), with revalidation of A. arenensis (Chace, 1937), Zootaxa 1694, pp. 51-68 : 59-62

Alpheus arenensis ( Chace, 1937)

Figs. 3E, 4B

Crangon arenensis Chace 1937: 119 , fig. 4.

Alpheus arenensis — Crosnier & Forest 1966: 236; Rodríguez de la Cruz 1977: 29; Carvacho & Ríos 1982: 282; Rodríguez de la Cruz 1987: 43.

Alpheus websteri (not sensu Kingsley 1880)— Wicksten 1983: 42 (part.); Wicksten & Hendrickx 1985: 572; Kim & Abele 1988: 28, fig. 11; Villalobos Hiriart et al. 1989: 17; Wicksten & Hendrickx 1992: 5 (part.); Wicksten 1993: 151; Hendrickx 1993a: 306; Hendrickx 1993b: 6; Hendrickx 1995: 432; Salazar-Rosas 1995: 59, pl. 17; Camacho 1996: 64; Vargas & Cortés 1999: 902; Villalobos 2000: 66, fig. 33; Wicksten & Hendrickx 2003: 65 (part.); McClure 2005: 157, fig. 24 (reproduced from Kim & Abele 1988).

FIGURE. 3. Color patterns of adult males of Alpheus websteri Kingsley, 1880 (A–D) and Alpheus arenensis ( Chace, 1937) (E); A–C, specimen from Dominican Republic (MNHN-Na 16362), A, general view, B, chelipeds, C, tail fan; D, specimen from Isla Grande, Caribbean coast of Panama; E, specimen from Isla Perico, Pacific coast of Panama.

Material examined.— Panama (Pacific coast). 1 male (CL 4.1), USNM 1109190, Las Perlas Islands, Saboga, shallow subtidal, from rock crevices, coll. A. Anker, J. Jara and C. Hurt, 15 Nov 2005 [fcn 05-156]; 1 male (CL 9.7), 1 female (CL 9.3), USNM 1109191, Amador Causeway near Panama City, Isla Perico, intertidal, coll. N. Knowlton et al., 22 Jan 1992 [fcn C-292 and C-293, B-68]; 1 male (CL 9.3), USNM 1109192, Río Mar, intertidal, coll. N. Knowlton et al., 16–20 Feb 1992 [fcn C-367, B-103]; 1 male (CL 8.7), USNM 1109193, same collection data as previous specimen [fcn C-363, B-99]; 1 male (CL 6.7), USNM 1109194, same collection data as previous specimen [fcn C-365, B-101]; 1 ovig. female (CL 6.5), MNHN-Na 16387, Coiba Marine National Park, Coibita, mud-rock intertidal, under rock, coll. A. Anker, I. Marin, J. Jara, E. Gómez and E. Tóth, 20 Mar 2007 [fcn 07-111].

Description.—See Chace (1937) as Crangon arenensis ; Kim & Abele (1988) as Alpheus websteri .

Color pattern.—Background color cream white or pale grey; carapace with two broad transverse chestnut to brown bands, one band at about mid-length, extending anteriorly on mid-dorsal line, and one more posterior band, constricted on anterior and posterior margins, and extending anteriorly dorsolaterally, almost reaching first band (Fig. 3E), defining “bikini” pattern in dorsal view; both bands abruptly changing direction on carapace flanks (Fig. 3E); two small short brown bands present anterolaterally, ventrally and posteroventrally to orbital hoods (Fig. 3E); rostral area also brownish, in particular rostral carina; inner organs visible through carapace dorsally as large brownish patch; articulation zone between carapace and abdomen and posterior carapace sharing white rhomboid patch on brown background (Fig. 3E); abdomen with six broad (except first) chestnut to brown transverse bands with concave margins, extending to ventral margin of pleurae, abruptly changing direction laterally (towards posterior) and nearly touching on flanks (Fig. 3E); second abdominal band bifurcating laterally, reverse V-shaped (Fig. 3D); sixth abdominal somite almost completely brown except for transversely elongate white patch (Fig. 3E); white bands between brown bands with sparse spots of pale-yellow chromatophores; tail fan mostly purple-brown with large white areas, proximal portion of telson and uropods whitish, dorsal spines whitish; distolateral spine black; walking legs and second pereiopods appearing pinkish semitransparent speckled with minute red chromatophores except on articulations; cheliped merus and carpus brown laterally; mesial face of palm of major chela mostly pale brown with white areas and brown patches and fairly large dark brown spots on distal half (Fig. 3E), most proximal portion of palm white; pollex brown with whitish tip; dactylus brown-white with dark spots proximally, pink distally (Fig. 3E); palm of minor chela brown-orange, with white areas and brown spots; fingers dark brown, paler towards tip; antennular peduncles brown distally, whitish proximally; basicerite and scaphocerite mostly whitish with occasional brown-orange spots, lateral margin and distolateral tooth of scaphocerite brown; antennular and antennal flagella pale brown; corneas dark brown-grey (Fig. 3E); juveniles similar, but with more contrasting pattern on chelae, carapace, abdomen and tail fan; yellow chromatophores more intense and forming transverse bands fringing brown-grey bands on carapace and abdomen (Fig. 4B).

Size.—The largest specimen from the Pacific coast of Panama is a male from Isla Perico with CL 9.7 mm, TL 24.8 mm. The CL of the Gulf of California specimens ranged from 4.4 to 8.0 mm, and TL from 17.0 to 21.6 mm ( Villalobos 2000).

Ecology.—Intertidal to about 6 m ( Wicksten 1983); in crevices of rocks and under coral rubble on sand or mixed sand-coral bottoms.

Type locality.—Arena Bank, Gulf of California, Mexico.

Distribution.—Eastern Pacific: Mexico: central and southern Gulf of California (e..g., Arena Bank, Sonora) and Revillagigedo Islands (Socorro) ( Chace 1937; Carvacho & Ríos 1982; Wicksten 1983; Wicksten & Hendrickx 2003); Costa Rica: Guanacaste, Puntarenas ( Kim & Abele 1988); Panama: Las Perlas ( Kim & Abele 1988; present study); Colombia ( Wicksten 1983); Galapagos ( Wicksten 1993; Wicksten & Hendrickx 2003).

Remarks.—The only noticeable morphological difference between A. websteri and A. arenensis lies in the development of the small distal tooth on the ventromesial margin of the major cheliped merus: acute in A.

websteri ( Fig. 1 H) and blunt or absent in A. arenensis (see Kim & Abele 1988, fig. 11f). A side by side comparison of two large adults of each species revealed two further, although very subtle differences: the orbital grooves appear to be deeper in A. arenensis compared to those of A. websteri , while the scaphocerite blade is shorter in A. arenensis compared to that of A. websteri , reaching to about 3/5 of the scaphocerite length (vs. 3/ 4 in A. websteri ). Differences in color between the two species are more numerous both in adults (Fig. 3D, E) and juveniles (Fig. 4A, B), including the more concave margins of the abdominal bands in A. arenensis (vs. almost straight in A. websteri ); the “bikini”-shaped posterior band on the carapace (this band is subrectangular in A. websteri ); and the presence of a white dorsomedian patch on the sixth abdominal somite (absent in A. websteri ) (see also Table 1 ).

GenBank number.— EU339466 [99-041, not deposited, Panama].

Feature A. websteri (WA) A. arenensis (EP) A. fagei (EA)

Figures

FIGURE 1. Alpheus websteri Kingsley, 1880, male from Isla Grande, Caribbean coast of Panama (USNM 1109181) (A – Q), male from Guadeloupe (MNHN-Na 16241) (R – T); A, frontal region, dorsal view; B, same, lateral view; C, tooth on ventromesial carina of first segment of antennular peduncle, lateral view; D, third maxilliped, lateral view; E, major cheliped, chela, lateral view; F, same, coxa to carpus, lateral view; G, same, chela, mesial view; H, same, detail of mesioventral margin of merus and carpus, mesial view; I, same, dactylus, lateral view; J, minor cheliped, lateral view; K, same, chela, mesial view; L, second pereiopod, lateral view; M, third pereiopod, lateral view; N, same, distal propodus and dactylus, lateral view; O, second pleopod, appendix masculina and appendix interna, mesial view; P, right uropod, dorsal view; Q, telson, dorsal view; R, frontal region, dorsal view; S, major chela, lateral view; T, minor chela, lateral view. Scale bars: 1 mm.