An examination of the shrimp family Callianideidae (Crustacea: Decapoda: Thalassinidea).

—One striking character was found to unite the members of the family Callianideidae, viz. the presence of rows of plumose setae, each seta sited in a pit, these rows being found on the carapace, abdominal pleura, and propodi of pereopods 2-4. Several new taxa are described: Crosniera, new genus (for Callianassa minima Rathbun, 1901); Michelea, new genus (for Callianidea vandoverae Gore, 1987, Callianidea leura Poore & Griffin, 1979, Callianidea lepta Sakai, 1987, plus the new species M. pillsburyi and M. lamellosa); Mictaxius, new genus (with the new species M. thalassicola); Marciisiaxius lemoscastroi Rodrigues & Carvalho, 1972, is redescribed, along with M. colpos, new species, while six species of Meticonaxius are discussed, with Meticonaxius bouvieri, new species described. A cladistic analysis of 11 taxa suggested that, within the Callianideidae, pleopodal respiratory filaments arose twice, that the linea thalassinica and the dentate ischial crest of maxilliped 3 have twice been lost, and that the Thomassinia-Crosniera-Mictaxius group of genera are most closely related to the Callianassidae. In the continuing effort to bring clarity to the systematics of the thalassinidean decapods, individual genera and families are being examined in detail (e.g., Kensley 1989, Kensley & Heard 1990). Morphological characters in particular are being reassessed, in an attempt to estabUsh relationships. With this objective in view, the western Atlantic members of the Callianideidae possessing accessory respiratory filaments of the pleopods were examined, but it became apparent that several thalassinidean species lacking these filaments should also be included in this group; the review was thus expanded beyond the western Atlantic. Of the group possessing respiratory filaments on the pleopods, the genus Callianidea is diagnosed, a new genus Michelea created to accommodate Callianidea vandoverae, two Pacific species, and two new species. In the group lacking pleopodal filaments, the species of the genera Meticonaxius and Marcusiaxius are reviewed or redescribed, and one new species of each described; the genus Thomassinia is examined, along with the seemingly closely-related ^Callianassa'' minima and the new genus Mictaxius. For comparative purposes, material of the Pacific Callianidea typa H. Milne Edwards, 1837, was examined from Bikini Atoll, Saipan, Guam, and Tahiti, as was the holotype o{ Callianidea lepta Sakai, 1987, from Japan (USNM 231419). Common to all these forms is the presence of short plumose setae, each seta sited in a pit-like structire, these pits usually arranged in tight rows. From hereon referred to, for the sake of brevity, as 'setal rows,' these rows are found on the anterolateral carapace, on the pleural region of each abdominal somite, and on the propodi of pereopods 2 ^ (Fig. 1). Amongst the callianideid genera, the arrangement and siting of these setal rows fall into three patterns, illustrated in Fig. 2. The number and position of exopods and 494 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON Fig. 1. SEM micrographs of Marcusiaxius colpos: A, Setal row from pleuron 2, 350 x; B, Setal row from propodus of pereopod 3, 150x; C, Setal row from propodus of pereopod 3, 250 x. VOLUME 104. NUMBER 3 495 Fig. 2. Diagrammatic representation of three patterns of setal row distribution on carapace and abdomen (above) and propodi of pereopods 2 ^ (below): A, Callianidea (pattern 0); B, Crosniera (pattern 1); C, Marcusia.xius (pattern 2). 496 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON Table 1. —Distribution of exopods, epipods, and gills.