The order Euryalida Lamarck, 1816 (Echinodermata: Ophiuroidea) comprises 4 families, 48 genera and about 190 species and is known from marine water. By the examination of type specimens of 117 species, taxonomy of euryalid genera and species from the Western Pacific are revised. With junior synonymizations of 2 species and descriptions of 1 genus and 5 species, a total of 120 species were recognized in this region. Molecular phylogeny based on mitochondrial and nuclear genes reviewed family-level systematics of the order.
Caprellidea have undergone a complicated morphological evolution. Most caprellid families exhibit strongly degenerated third and fourth pereopods (walking thoracic limbs) and abdomens. However, a caprellid family, Caprogammaridae, has developed abdominal segments with swimming appendages, whereas another family, Phtisicidae, possesses well-developed third and fourth pereopods. We conducted molecular phylogenetic analyses of caprellid families and ancestral state reconstruction. The analyses suggested that third and fourth pereopods in Phtisicidae and the abdomen in Caprogammaridae might be regained. The embryonic development of Caprella scaura was observed in order to understand the developmental and genetic mechanisms involved in the complicated morphological evolution of Caprellidea. In the embryonic development of C. scaura, distinct abdominal segments did not appear. In addition, elongation and segmentation of limb buds did not occur in the third and fourth pereonites (free thoracic segments), although the primordial gills appeared. These observations indicate that the telopods were not formed in the third and fourth pereonites. In order to confirm this hypothesis at the molecular level, gene expression analyses of Distal-less was performed and it was observed that Dll was not expressed in the third and fourth pereonites. This is the first molecular phylogenetic and developmental study focusing on the morphological evolution of Caprellidea.
A method to observe animal internal tissues of alcohol specimens is proposed using resin impregnation and geological grinding technique. Animal specimens were embedded in Spurr resin and ground to expose the internal organs. In this method, both hard and soft tissues can be simultaneously observed by using a stereo-microscope. Thin sections of the specimens were also prepared for transmitted-light microscopy. This method can retain the texture and color of the tissue. It was applied to an ophiuroid with calcite skeleton, a sponge with silica skeleton, and a beetle with hard cuticle exoskeleton.