Alpheus aequus Kim & Abele, 1988

Anker, Arthur, Hurt, Carla & Knowlton, Nancy, 2007, Three transisthmian snapping shrimps (Crustacea: Decapoda: Alpheidae: Alpheus) associated with innkeeper worms (Echiura: Thalassematidae) in Panama, Zootaxa 1626, pp. 1-23 : 17-19

Alpheus aequus Kim & Abele, 1988

Figs. 10 , 11 f

Alpheus aequus Kim & Abele, 1988: 55 , fig. 23; Wicksten & Hendrickx, 1992: 4; Ramos, 1995: 145, fig. 9; Vargas & Cortés, 1999: 898; Wicksten & Hendrickx, 2003: 63.

Material examined. 1 female (CL 4.7, TL 14.3), MNHN-Na 16388, Panama, Coiba Marine National Park, Coibita, mud-rock intertidal, under rock, in burrow of Ochetostoma edax (host collected and preserved), extreme low tide, 20 Mar 2007, coll. A. Anker, I. Marin, J. Jara, E. Gómez and E. Tóth [fcn 07-109]; 1 ovig. female (CL 4.9, TL 14.3), MNHN-Na 16389, Panama, Coiba Marine National Park, Coibita, mud-rock intertidal near STRI station, under rock, in burrow of Ochetostoma edax (host collected and preserved), extreme low tide, 22 Mar 2007, coll. A. Anker [fcn 07-177].

Description. For detailed description see Kim & Abele (1988).

Color. Mostly ivory-whitish with pinkish tinge in some areas due to presence of scattered reddish chromatophores ( Fig. 11 f); one female had yellow-orange eggs.

Size. The CL of the two females is 4.7 mm and 4.9 mm, the TL for both is 14.3 mm. The single male originally reported by Kim & Abele (1988) had a CL of 4.3 mm, whereas the two females both had a CL of 6.8 mm. Ramos’ (1995) three specimens were smaller, with 2.9 mm CL in the single male and 4.3–4.4 mm in the two females. Based on these data, the CL of adult A. aequus ranges from 2.9 to 6.8 mm.

Type locality. Playa Blancas, Costa Rica ( Kim & Abele, 1988).

Distribution. Eastern Pacific: Costa Rica: Playa Blancas; Galapagos: Santa Fe ( Kim & Abele, 1988); Panama: Coibita (Coiba Marine National Park) (present study); Colombia: Gorgona Island ( Ramos, 1995).

Ecology. The habitat of the holotype from Playa Blancas, Costa Rica, was described as “shore to 5.0 m; shale beach” and “shale beach between beach and rocky reef” ( Kim & Abele, 1988). Other alpheids collected in this area were Alpheus fasciatus Lockington 1878 (reported as A. paracrinitus Miers, 1888 ) and A. galapagensis Sivertsen, 1933 (reported as A. canalis Kim & Abele, 1988 ). The two specimens from Santa Fe (Barrington) Island, Galapagos, were collected while “diving in bay, [at] about 5 m ”. Other alpheids occurring in this locality were Alpheus bellimanus Lockington, 1878 and A. rostratus Kim & Abele, 1988 . Ramos’ (1995) specimens came from a tidal beach with coral sand (“playas de arena coralina”). No particular associations were noted by Kim & Abele (1988) or Ramos (1995). In contrast, the two Panamanian specimens of A.

aequus were found associated with medium-sized (body length 28 mm, diameter 11–12 mm, proboscis length 15 mm, proboscis diameter 3–5 mm) thalassematid echiurans, Ochetostoma edax (Fisher, 1926) ( Fig. 12 e) in a mixed mud-rock intertidal of Coibita ( Fig. 12 d). The burrows of O. edax are smoothly lined horizontal tunnels dug in muddy sand under partly mud-embedded rocks. The shrimps were observed sitting just next to their hosts. Notably, in both cases, only one shrimp per host was found, despite some efforts to find its potentially present mate by prospecting the immediate vicinity of the burrow.

Taxonomic remarks on host. The finding of two specimens of Ochetostoma edax (identification by G.-V. Murina) at Coibita represents a considerable extension of the distribution range of this species from Baja California to Panama. The identity of O. cf. edax from the Atlantic (Caribbean) coast of Panama remains to be determined (see above).

Variation. The two female specimens from Coibita agree well with the description and illustrations of A. aequus provided by Kim & Abele (1988), except for the length of the dactylus of the major chela, which reaches only slightly beyond the tip of the pollex in the Coibita specimens, and distinctly beyond the pollex in the holotype (cf. Kim & Abele 1988, fig. 23).

GenBank number. EU084881 (fcn 07-109, MNHN 16388).

Figures

FIGURE 10. Alpheus aequus Kim & Abeke, 1988, female from Coibita, Coiba Marine National Park, Panama (MNHN 16389): a, frontal margin, dorsal view; b, major cheliped, lateral view; c, same, chela, mesial view; d, minor chela, lateral view; e, second pereiopod, lateral view; f, third pereiopod, lateral view. Scale bars: 1 mm.

FIGURE 11. Color patterns in life. Alpheus christofferseni n. sp., male from Bocas del Toro, Panama (USNM 1100667) (a – c): a, b, dorsal view (note partly faded chromatopores in a); c, same, lateral view. Alpheus naos n. sp., male holotype from Punta Culebra, Isla Naos, Panama (USNM 1100668) (d, e): d, dorsal view; e, lateral view. Alpheus aequus Kim & Abele, 1988, female from Coibita, Coiba Marine National Park, Panama (MNHN-Na 16389) (f): dorsal view.

FIGURE 12. Habitats and hosts: a, shallow subtidal sandflat with patches of flotting algae and seagrass at Carenero Island, Bocas del Toro, Panama, type locality of Alpheus christofferseni n. sp.; b, c, Alpheus christofferseni n. sp. with host, Ochetostoma cf. edax (Fisher, 1946) (Echiura, Thalassematidae), a few hours after collection; d, partly exposed rock-mud intertidal at Coibita, Coiba Marine National Park, Panama, one of collection sites of Alpheus aequus Kim & Abele, 1988; e, Ochetostoma edax (Echiura, Thalassematidae), host of the Coibita specimen (MNHN-Na 16389).