Functional aspects of behavior and morphology in the decorator crab Microphrys bicornutus (Latreille, 1825) (Crustacea: Brachyura: Mithracidae)

Masking or decorator crabs, conceal themselves partially through camouflage, by selecting or indiscriminately attaching materials from their environment to their exoskeleton. Functional aspects of decorating behavior and morphology in this group have not been documented. Using Microphrys bicornutus as a model species, this dissertation demonstrates clearly that decorating is an advantageous phenotype that has evolved to serve several functions.;Decorating is a complex behavior that begins when a crab approaches an algal substrate and results in the attachment of algae to hooked setae on the exoskeleton. Once decorated, crabs remain motionless on the substrate until disturbed or until another behavior is initiated. This was confirmed for M. bicornutus, as crabs spent a significant amount of time feeding, remaining motionless, picking, and walking when compared to decorating. Crabs displayed agonistic behaviors during encounters with conspecifics conspecifics. These included both active aggressive behavior and display behavior. Crabs showed a decrease in motility during these encounters, helping maintain dispersed distributions, thereby decreasing intrsapecific encounters in the field.;Trials were done to determine the effect of conspecifics, predators and feeding preferences on algal utilization. M. bicornutus showed a significant decrease in the amount of algae used for decoration in the highest density trials (i.e., 4 and 8 crabs). Agonistic displays and aggressive behavior between these crabs likely affected the time available for decorating. Decorated crabs isolated from an algal substrate were more likely to survive in the presence of either of two sympatric fish predators. Thus, being protected by the algal decoration on their exoskeletons. Trials also showed a parallel between algal consumption and algal materials used for decoration. In addition to its protective function, algae used by M. bicornutus for decoration simultaneously serve as short term food supplies for the crabs.;Eleven morphologically complex structures were identified and mapped on the exoskeleton. Hooked setae were the primary structures used to attach algae to the crab's body. Ten additional setal structures were present, including two novel types of setae. On the basis of location and morphological variation exhibited among these latter structures, a primary sensory function may be inferred.