Alaocaris Holthuis, 1949

Grave, Sammy De & Ashelby, Christopher W., 2013, A re-appraisal of the systematic status of selected genera in Palaemoninae (Crustacea: Decapoda: Palaemonidae), Zootaxa 3734 (3), pp. 331-344 : 340

Comments on Alaocaris Holthuis, 1949 and Calathaemon Bruce & Short, 1993

Holthuis (1949) erected Alaocaris as a subgenus in Palaemonetes , for the Texan cave dwelling species, Palaemonetes antrorum Benedict, 1896 . Strenth (1976) however, considered three out of the four distinguishing features of the subgenus to be regressive characters linked to the subterranean environment of P. antrorum , with the remaining character, the absence of a movable spine on the exopod of the uropod, showing considerable variation across the genus, even amongst North American epigean species of the genus. Logically, he therefore synonymised both subgenera, an action generally followed since then in all major compilations.

Bruce & Short (1993) erected the genus Calathaemon for the aberrant subterranean species Palaemonetes holthuisi Strenth, 1976 ; which was subsequently placed in the family Kakaducarididae by Bruce (1993), although with some reservation. As discussed below, following Short et al. (2013), Calathaemon is herein transferred to Palaemoninae , which potentially raises a further taxonomic issue. Short et al. (2013) drew attention to the fact that despite the unique mouthpart morphology of C. holthuisi , this species, morphologically at least, most closely resembles the sympatric P. antrorum , which could either be due to convergent evolution or a phylogenetic link between both species. Should these taxa indeed form a distinct clade separate from Palaemon sensu lato (as herein defined), then the generic name Alaocaris Holthuis, 1949 would take priority over Calathaemon Bruce & Short, 1993 . Alternatively, both species may belong to Palaemon sensu lato, with their morphologies being unique adaptations to their subterranean environment, as indeed was the view of Strenth (1976). Currently, this cannot be resolved, as neither species could be included in the phylogeny of Ashelby et al. (2012) and further fresh material suitable for genetic analysis has not been forthcoming. For now, the genus Calathaemon is thus treated as valid and monotypic, primarily supported by its unique mouthpart morphology, whilst P. antrorum is herein transferred to Palaemon .