THE USE OF CUTICULAR CHARACTERS IN DECAPOD PHYLOGENY

Development of a robust character matrix for fossil decapod crustaceans that parallel characters used in the phylogenetic analyses of extant taxa has been hampered by the vagaries of fossil decapod preservation. In the best of circumstances, when the entire exoskeleton of the decapod is fossilized, identification and classification still pose problems because the classification of extant taxa is based upon molecular, developmental, soft-part, or delicate morphological structures that are seldom preserved or accessible in fossils. This study examines the microstructural variations within cuticle of decapod crustaceans in order to identify innovative character states in fossil and extant organisms that can be observed, coded, and included in phylogenetic analyses. The primary hypothesis to be tested is that there is a unique set of phylogenetic characters in the cuticular architecture of decapod cuticle that be incorporated into phylogenetic analyses of both fossil and living taxa. These characters of the cuticle include features observable on the surface (nodes, pits, and perforations of the cuticle associated with setal hairs) and those observed within the cuticle (node construction and disposition of cuticular sublayers). Analysis of these characters is ongoing, but preliminary results suggest that the structure of the exocuticle provides characters that differentiate the shrimp, crabs, and lobsters, and that these differences are observable in both fossil and extant material. Surficial characters, in addition to characters regarding their corresponding internal construction, show a phylogenetic signal, but convergence makes them irrelevant at lower taxonomic levels. Features that appear similar on the surface may be constructed in different manners and may involve different layers of the cuticle, and thereby can be differentiated with the addition of internal characters to provide additional resolution. In general, it is clear that characters of the decapod cuticle do provide some phylogenetic signal and are worth incorporating into phylogenetic studies that utilize a broader array of morphological and molecular characters.