Pontonia panamica n. sp., is described on the basis of 14 specimens from the Pacific coast of Panama. The new species associates with sea squirts, Ascidia cf. interrupta Heller, 1878 (Ascidiidae) attaching underneath rocks partly submerged in silty sand in the lower intertidal. Pontonia panamica n. sp. is closely related to P. longispina Holthuis, 1951 from the Gulf of California, but can be distinguished from the latter species by the absence of a subdistal tooth on the ventral margin of the rostrum; the more developed distolateral tooth on the first antennular segment; the longer proximal segments in the endopod of the second maxilliped; the dactylus of the minor cheliped with one simple triangular tooth on the cutting edge; and the comparatively longer carpi of both minor and major chelipeds. The recently proposed phylogeny of Pontonia (Fransen 2002) and the association of P. panamica n. sp. with an ascidian host suggest a host switch from Ascidiacea to Mollusca relatively early in the evolutionary history of this genus.
Crustacea, Decapoda, Caridea, Palaemonidae, Pontoniinae, Pontonia, eastern Pacific, Panama, symbiosis, ascidians, host switch, new species.