Ontogenetic Variations in Cuticle Morphology in the Blue Crab Callinectes Sapidus Rathbun, 1896

Abstract

In an effort to use aspects of the cuticle as taxonomic characters in phylogenies of fossil and extant decapods, variation due to gender, growth, sample location on the carapace, and molt cycle must be understood so that taxonomically important characters can be identified. In this study, effects of sample location on the carapace and carapace size were examined. A series of male Callinectes sapidusRathbun, 1896, specimens from |${\text{2}} - {\text{6}}\,\,{\text{cm}}$| in length were collected on the Rhode River of the Chesapeake Bay, MD, USA. To study the effects of sample location and carapace size on parameters of the cuticle, the cuticle was examined in thin section and on the surface of the dorsal carapace. The distributional density of setal pits and nodes and node size were measured on the surface. In thin section, thickness of the cuticle and construction of the nodes and setal pits was examined. Thickness of the cuticle, node size, and setal pit density increased during growth of the crab. Node density decreased with growth. Construction of nodes and setal pits remained constant in all specimens and sample locations. Morphometric parameters of the cuticle were consistent with previously reported growth rates of the carapace in C. sapidus. Differences in the rate of change for the cuticle metrics studied occurred at carapace sizes that are attained upon reaching sexual maturity. Growth rates of cuticular features provide context for comparison with similar data in other species. In addition, the change in growth rates of these features, if recognized in fossil crab populations, may allow the determination of population age structures and size at maturity.