Decapods are the most diverse and complex group of crustaceans, adapted for life in all parts of the marine environment, many aquatic habitats, and some terrestrial niches. With this diversity of life styles, a vast range of morphotypes of decapods has evolved, exploiting almost every imaginable variation in morphology of the complex exoskeleton that characterizes them. Many of the morphological variants are a response to exploiting a particular niche in which the organisms live or an adaptation to particular behavioral characteristics. Assessing the significance of morphological variation in the fossil record is challenging because of the taphonomic overprint that results in loss of soft tissue, preservation of partial remains of hard parts, and vastly reduced numbers of preserved individuals as contrasted to the once-living population. The purpose of the present paper is to identify aspects of morphology that may be useful in interpreting the behavioral responses of the organism to its environment, w,th primary emphasis on morphological features of the exoskeleton that are not expressed on all individuals but that occur at low, and unpredictable, frequencies.