Arhythmorhynchus frassoni (Molin, 1858)

(Fig. 8)

Localitiy. SINALOA: Laguna el Caimanero.

Specimens deposited. CNHE 7711.

Remarks. The 5 specimens collected in the present study correspond to Arhythmorhynchus frassoni. This species is characterized by having a long slender body, divided in 2 regions by a constriction, and by having a spined foretrunk, a fusiform proboscis broadening at the base, armed with 18 longitudinal circles of 20 hooks each. The ventral hooks at base of the proboscis are larger than the rest, and the neighboring lateral hooks are smaller than the rest (Petrochenko 1958; Nickol & Heard 1970; Nickol et al. 2002). The specimens recovered in this study are immature, possibly indicating that Eudocimus albus may represent an accidental host for A. frassoni. The distribution area of A. frassoni includes Florida, and the Yucatan Peninsula in Mexico. It has also been reported as larval stage in the fiddler crab Uca rapax (Smith) (Nickol et al. 2002) and the spined fiddler crab Uca spinicarpa (Rathbun) (Guillén-Hernández et al. 2008). Adults of A. frassoni have been previously found in Rallus longirostris Boddaert from Southeastern North America (Nickol & Heard 1970; Nickol et al. 2002). The present record extends its distributional range into the Pacific Ocean slope, since it was already found in Laguna el Caimanero, Sinaloa, Northwestern Mexico.