Systematic Evaluation of Raninid Cuticle Microstructure

Studies of decapod cuticle microstructure in both the paleontologic and neontologic literature generally focus on understanding cuticular construction and recognizing these features in fossil material. We examine the cuticle of 57 species in 26 genera within the Raninoidea. Within each genus cuticle microstructure of raninids is generally similar, but in successively higher taxonomic groups, greater variance is seen within and between groups. The subfamily Lyreidinae contains microstructures limited to pits and upright nodes. The Paleocorystinae contains species with predominantly upright nodes and cuticle that generally differs from the other subfamilies. The remaining subfamilies, including the Ranininae, Raninoidinae, Cyrtorhininae, and Notopodinae, are generally similar in their cuticle microstructure; they exhibit inclined nodes, and various combinations of pits, setal pits, depressions, and perforations. The Symethidae contains fungiform nodes, similar to those seen in Cretacoranina, a genus within the Paleocorystinae. Traditional taxonomic characters clearly separate the subfamilies of the Raninidae as well as separating the Raninidae from the Symethidae. Similar cuticle microstructures may appear in different subfamilies. Based upon cuticle microstructure alone, the Raninidae can be divided into three, morphotypes; the Paleocorystinae with upright and fungiform nodes, the Lyreidinae with pits and upright nodes, and the Ranininae, Raninoidinae, Cyrtorhininae, and Notopodinae with inclined nodes. Morphometric study of characters on the surface of the cuticle shows that features such as nodes and pits generally increase in size during the growth of the organism with a concomitant decrease in distribution density. Features of the cuticle change both across a single carapace and during growth of the organisms. Cuticle microstructures that are seen to grade into one another are considered to be part of a morphological continuum. Those structures that do not appear on the same carapace or during successive instars are not part of a morphological continuum.