Aspects of myodocopin (Ostracoda) biology and crustacean iridescence

This study describes the following discoveries I made while working on cypridinid ostracods, and subsequently other crustaceans. -- Two new cypridinid genera, Cohenia and Lowrya, containing the species C. taiti and L. kornickeri, and a new species of cypridinid, Vargula karamu, are established. The genus Cohenia bears an unusual type of sensilla, termed a trichocoel. Trichocoels may be velocity detectors, which detect either steady fluid drainage motion or acoustic motion in the surrounding water. The furca is used as a major feeding tool in scavenging cypridinids. The hard section of the dorsal body wall almost adjacent to the furca in all myodocopins is termed the sclerosome. The sclerosome provides support for certain fureal muscles, and protection for the soft body when the carapace is opened. The central adductor muscles of myodocopins, are arranged as a group of small muscles, rather than a single large muscle, allowing different areas of the anterior, ventral, and posterior carapace margins to open almost independently of each other. The sensory seta of the fifth article of the myodocopin first antenna is termed the sseta. Setules of the s-seta, and some from other long first antennal setae, have a finely ringed ultrastructure and are termed halophores. The halophores of one first antenna are collectively termed the halothalium. The grooved external surface of a halophore acts as a diffraction grating, and causes highly efficient iridescence. This iridescence is functional during courtship in at least some cypridinids. Some cypridinids copulate in a position where ventral carapace margins are juxtaposed, and anterior ends are opposite. Copulation in these ostracods is completed in about five seconds. The cypridinids have evolved with light as a major stimulus. Based on phylogenetic studies, iridescence appears to be a precursor to cypridinid bioluminescence, and the myodocopin compound eye may have evolved independently. Iridescence is widespread throughout the Crustacea, occurring as a result of external diffraction gratings, or internal multilayer reflectors.