Biphasic moulting in isopods confers advantages for their adaptation to various habitats and lifestyle
Isopoda, a widely distributed crustacean order, exhibits the unusual biphasic moulting in which the posterior part of the exoskeleton constantly sheds before the anterior region. This paper presents a literature review on isopods, emphasizing the association of the biphasic mode of moulting with the adaptation of isopods to different habitats and lifestyles. Owing to the biphasic pattern of moulting, the two halves of the body take shifts to carry out essential functions such as oxygen consumption, resorption of cuticular calcium, evading the risk of water loss, and compartmentalising the processes of moulting and mating. Biphasic moulting is also advantageous for the parasitic isopods to cling to their host, regulate their feeding habitat and taxis, resist water flow, withstand strong forces in their microhabitat and synchronize mating. Histology and enzyme-linked immunosorbent assay (ELISA) experiments conducted in few isopods demonstrated the differential responses of anterior and posterior body parts to neurohormones such as ecdysteroids. Taken together, the conserved phenomenon of biphasic moulting in isopods should offer several advantages for adapting to diverse environments even though there is no direct evidence.