Taxonomy and Phylogeny of Dicyemid Mesozoans

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(1) Description of new species of dicyemids.Ten new species of dicyemids were described from Sepioteuthis lessoniana, Sepia latimanus, Amphictopus areolatus, A.kagoshimensis, and A.fangsiao in Japanese seas.(2) Phylogenetic and evolutionary studies on dicyemidsThe calotte morphology of dicyemids appears to result from adaptation to the structure of host renal tissues and help to facilitate niche separation of coexisting species.In most dicyemids distinctly small numbers of sperms are produced in a hermaphroditic gonad (infusorigen). The number of eggs and sperms are roughly equal. All inverse proportional relationship exists between the number of infusorigens and that of gametes, suggesting a trade-off between them.The renal organs of 32 species of cephalopods were examined for parasite fauna and for histological comparison. Two phylogenetically distant organisms, dicyemid mesozoans and chromidinid ciliates, were found in 20 cephalopod species. Most benthic cephalopods (octopus and cut … More tlefish) were infected with dicyemids. Dicyemids and chromidinids attach their heads to epithelia or insert their heads into folds of renal appendages, pancreatic appendages, and branchial heart appendages. The rugged and convoluted external surface provides a foothold for dicyemids and chromidinids with a conical head. They apparently do not harm these tissues of their host cephalopods.Cell numbers and cellular composition were examined in infusoriform larvae of 44 species of dicyemid mesozoans belonging to 6 genera ; Conocyema, Dicyema, Dicyemennea, Dicyemodeca, Mocrocyema, and Pseudicyema. Infusoriform larvae consist of a constant cell number which is species-specific. Small interspecific variations are found in total cell numbers, 35, 37, 39, 41, and 42. Most differences in total cell numbers are due to the absence or presence of particular ventral cells. In all infusoriform larvae, the lateral, dorsal and caudal areas are cell constant, whereas in the apical and ventral areas a distinct and variablc configuration of cells are present. Less