COMPARISON OF MORPHOLOGICAL CHARACTERISTICS OF THE DORSAL CARAPACE OF SPONGE CRABS (DECAPODA: BRACHYURA: DROMIACEA) USING MULTIVARIATE ANALYSES

The superfamily Dromioidea (Decapoda, Brachyura) includes six families of true crabs that first appeared in the fossil record during the Aptian (Early Cretaceous). Members of the family Dromiidae are well known in modern oceans as sponge carriers that utilize a reduced and sub-dorsal 5^th pereopod in order to hold onto the sponge. Along with these characteristics it has been observed that the pleon is extended laterally from the carapace instead of tightly tucked under. This extension aids in the rotation and placement of the 4^thand 5^th pereopods. Though the pereopods are often not preserved in fossil specimens, the pleon is. Characters of the dorsal carapace are hypothesized to be indicative of carrying capabilities in the absence of a sponge preserved alongside dromioids in the fossil record; testing that hypothesis is ongoing. Principle component analysis and PCoA were used to analyze over 90 species using more than 30 characters from coding characteristics of the dorsal carapace, pereiopods, and pleon. This constitutes over 50% of the known genera; the goal is to analyze at least one member of each dromioid genus. This analysis has demonstrated that ornamentation and development of carapace regions is most important in grouping species together. Preliminary data suggest there is no significant difference in arrangement of fossil members when analyzing both fossil and modern members together versus plotting fossils independently. The placement of many fossil members into families have been contested over the years, and in this analysis, members of Dynomenidae and Dromiidae become intermixed while other, extinct families have better defined groupings. Preliminary data suggests that some members of Dromiacea incerte sedis can be confidently placed within the families of Dromioidea. It was previously hypothesized that members of Dromioidea changed in overall carapace size through time. A t-test of carapace width and length of fossil versus extant specimens indicates that no change has occurred. This ongoing study of the superfamily is providing new information and shedding light on common characteristics found in fossil and modern members.