Review of the Genus Polycheria Haswell, a Symbiotic Group of Amphipods (Crustacea: Dexaminidae) With Descriptions of New Species from Florida, the Caribbean Sea, and the Indo-Pacific Region
Systematics and taxonomy of the dexaminid amphipod genus Polycheria Haswell (Dexamindae: Amphipoda), whose members are cosmopolitan associates of tunicates and sponges, are confused. This is due in large part to the many inadequate and incomplete descriptions and poorly some executed illustrations, especially for the early studies on the group. Previously, 22 nominal species or forms have been described or designated in the literature. The purpose of this study is to critically review and clarify the systematics of this enigmatic genus. Based on personal collections and on specimens from museums, five new species are designated and 22 species or forms are re-described. All the species and forms of Polycheria are illustrated and a dichotomous key constructed for their identification. For cladistic analysis, a suite of 77 morphological characters were selected and coded in DELTA. Analysis was preformed using PAUP, including strict consensus, 50% majority rule, and decay indices. The resulting best tree indicated that Polycheria is a monophyletic group characterized by (1) subchelate pereopods 3-7; (2) absence of palp on maxilla on the mandibles; (3) lower lip inner and outer lobes well developed; (4) a one-articulate palp on maxilla 1, and (5) and a 4-articulate palp on the maxilliped. The hypotheses presented, based on the currently understood distribution of Polycheria , the current and historical position of the continents and major oceanic currents, and the majority rule consensus tree generated from 77 parsimonious characters, indicates that (1) Polycheria had its origins in the Southern Ocean between Antarctica and the Australia/New Zealand area; (2) the dispersal of the ancestral Polycheria genotype occurred along at least two tracks--a circumpolar track eastward around Antarctica, driven by the Antarctic Circumpolar Current and along a northern track around New Zealand, along the east coast of Australia, into the Australasian region, and eventually northward to the Sea of Japan; and (3) the Antarctica peninsula appears to be an area of high speciation from which dispersals eastward into the Indian Ocean and possibly Australia originated.