A New, Sibling Species of Snapping Shrimp Associated with the Caribbean Sea Anemone Bartholomea Annulata

Alpheus immaculatus, a new species of snapping shrimp associated with the Caribbean sea anemone Bartholomea annulata, is described and figured. This new species, together with the well known Alpheus armatus, and a much rarer, as yet undescribed, third species, make up a complex of sibling species that share the same host and are extremely similar morphologically. A small set of distinctive color pattern differences unambiguously distinguishes these species when alive, and one morphological character can also be used to distinguish the two species in most preserved specimens. No reproductive pairings between species have been observed in the field. In the laboratory, adult males and females of different species behave very aggressively towards each other, in contrast to the placid interactions between conspecific, adult, male-female pairs. The distribution of A. immaculatus is wider with respect to depth than that of A. armatus. Deeper than 15 m, including all collections from anemones seaward of the reef crest, only A. immaculatus has been found. In many shallower backreef areas, A. armatus and A. immaculatus occur microsympatrically, although in some locations only A. armatus is found.