Dicyemid mesozoans are endoparasites, or endosymbionts, found only in the renal sac of benthic cephalopod molluscs. The body organization of dicyemids is very simple, consisting of usually 10 to 40 cells, with neither body cavities nor differentiated organs. Dicyemids were considered as primitive animals, and the out-group of all metazoans, or as occupying a basal position of lophotrochozoans close to flatworms. We cloned cDNAs encoding for the gap junction component proteins, innexin, from the dicyemids. Its expression pattern was observed by whole-mount in situ hybridization. In adult individuals, the innexin was expressed in calottes, infusorigens, and infusoriform embryos. The unique temporal pattern was observed in the developing infusoriform embryos. Innexin amino acid sequences had taxon-specific indels which enabled identification of the 3 major protostome lineages, i.e., 2 ecdysozoans (arthropods and nematodes) and the lophotrochozoans. The dicyemids show typical, lophotrochozoan-type indels. In addition, the Bayesian and maximum likelihood trees based on the innexin amino acid sequences suggested dicyemids to be more closely related to the higher lophotrochozoans than to the flatworms. Flatworms were the sister group, or consistently basal, to the other lophotrochozoan clade that included dicyemids, annelids, molluscs, and brachiopods.

Two new species of freshwater gastrotrichs are described from rice paddies in Otsu, Shiga, Japan. Lepidodermella acantholepida n. sp. is a medium sized species attaining a length of 145 μ m, scales are flattened ovals and similar to those of L. squamata except that two dorsal scales near the furca have a claw-like spine. Dichaetura filispina n. sp. is a medium sized species attaining a length of 185 μ m, characterized by a thin, fiber-like spine, a spined furca with a constriction near its base and an elongate body. A total of 44 species (seven genera) including two new species were found in the rice paddies. The diversity of rice paddy gastrotrichs is briefly discussed.

Two new species of freshwater gastrotrichs are described from a pond in Osaka, Japan. Chaetonotus retiformis n. sp. is a medium size species attaining a length of 180 μm, characterized by a three-lobed head with a single tuft of sensory cilia on each side and small scales with four long spines on the base of each member of the furca. Chaetonotus machikanensis n. sp. is a small size species attaining a length of 110 μm in length, characterized by a five-lobed head with a two tufts of sensory cilia on each side and large scales with long barbed spines.

No abstract