High species diversity and unique ecological characters of interstitial Ostracoda was introduced here. Although the number of reports on interstitial Ostracoda especially from Japan has been small yet, the recent researches by the author strongly suggest the existence of a huge number of undescribed interstitial ostracods. The number of interstitial species might surpass that of surface dwelling one in not only Ostracoda but also in other taxa. The two species of interstitial ostracods show a wide tolerance to in salinity, but they cannot live where fine sand (mode of grain size less than 1/8 mm) is the dominant particle size. In assays of phototaxis, one species which has a naupliar eye showed negative phototaxis.
The cytheroid Ostracoda is known as one of the major taxa in interstitial fauna. The evolution from surface dwelling taxa to the interstitial one is defined as "interstitialization" here. In order to resolve how "interstitialization" was achieved in the evolutionary history in Cytheroidea, the phylogenetical positions of the interstitial cytheroids were analyzed by the molecular phylogeny based on the nuclear 18S rDNA region. As a result, it was revealed that the interstitial taxa were independently and frequently derived from various positions in the cytheroid lineage. This result suggests that the dorso-ventrally depressed carapace shared in some interstitial taxa was developed as a result of parallel evolution, and that the "interstitialization" caused the high taxonomical diversification of Cytheroidea. Thus the "interstitialization" is an important change for the adaptive radiation of cytheroid lineage. The viewpoint of frequent "interstitialization" can become a reason why the high diversity of the interstitial fauna.
Reproductive isolation and evolution of copulatory organ in eleven interstitial species of the genus Parapolycope (Ostracoda, Myodocopida) were discussed. The shapes of male ejaculatory duct are divided into the three types i.e., a helical tube type (Type H), a curved short tube type (Type S), and tapering long tube type (Type L). And the correlation between the shapes of copulatory organs in both sexes is recognized as, what we call, the "lock and key". After copulation, the female genital openings of Parapolycope sp. 2 are often blocked by a rod-shape structure. The rod-shaped structure is thought as a part of the male copulatory duct. The phylogenetic relationships of several Parapolycope species were estimated by the mitochondrial COT gene sequences. According to this, the extremely long type of copulatory duct must have evolved gradually from the short curved tube type. As a hypothesis to explain the development of the extremely long type of ejaculatory duct, the concept of an "evolutionary arms race" would be applicable.
The interstitial ostracods and copepods have degenerated nauplius eye. The ultrastructure and ontogeny of their nauplius eyes are described here, using the transmission electron microscopy. The observations, found degenerative nauplius eyes in the both taxa. According to the comparison between the embryogenesis of normal nauplius eyes and the post-embryogenic development of degenerative nauplius eyes, it is strongly suggested that the degeneration is derived by paedomorphic evolution. Based on these observations as well as on some previous researches, I propose a hypothesis of the modularity, as hierarchical interactions in the nauplius eye.
Soil is a home to extraordinary high diversity of organisms. Soil structure has been modified by bioturbation of soil organisms and this structure determines assemblage of soil organisms. Experimental disturbance of soil structure modified the abundance of soil microarthropods and soil process; nitrogen mineralization and decomposition of organic matter, therefore conservation of surface soil structure is crucial for protection of soil biodiversity.
Marine caves and hyperbenthic layers harbor highly unique and diversified crustacean communities and accommodate both ancestral and advanced forms, suggesting repeated colonization to these habitats through the geological time. Some of the primitive groups show a Tethyan track. Remipedes and other crustaceans such as mictaceans are exclusively endemic to marine caves, taking advantage of caves as refuges. Truly cavernicolous crustaceans could have originated directly from shallow hyperbenthic, interstitial or crevicular ancestors or indirectly from the shallow- throughout the deep-water forms. Copepods can be regarded as one of the best model animals to understand the colonizing processes and patterns in these habitats, due to ample data on the distribution and phylogenetic analyses. These habitats have been intensively surveyed in the Mediterranean Sea, the Canary Islands, Burmuda, the Yucatan Peninsula, the Caribbean Sea, the Galapagos Islands and western Australia, but not so in East Asian waters. Hence taxonomic and phylogenetic investigations of these crustaceans should be addressed in Japanese waters to clarify their origins, colonization routes and evolutionary patterns and processes.
Upper Ordovician cave-dwelling trilobite species, Isocolus sjoegreni, Ityophorus undulatus and Prionocheirus obtusus, found in originally subsurface open-spaces of the Boda Limestone, Sweden, show two distinct occurrence patterns. Blind and dwarfed I. sjoegreni and I. undulatus co-occur with non-trilobite animal taxa, the former with ostracods and the latter microgastropods, which indicates ecological similarity with the taxa such as in preferable food resources. The two species show morphological simplification in their cephalic suture pattern, which is alike to the general morphological characteristics recognised in the modern cryptobionts. P. obtusus is generally found in a fossil assemblage that consists exclusively the specimens of the species. No other than its dwarfed body size, P. obtusus shows no corresponding morphological characteristics that are exhibited in the other two cave dwelling trilobite species. Its ancestral habitual characteristic, living in a deeper-water and stagnant muddy level bottom environment, is an indication that the species preferred on physical aspects of cryptic environments such as darkness and lack of predators. There appeared at least two general directions for the biodiversity of fossil cryptobionts.
The biology of Nymphonella tapetis Ohshima, 1927, a pycnogonid endoparasitic on some bivalves, is reviewed. After the first discovery of this species from Hakata Bay, Fukuoka in 1926, there were scattered records of N. tapetis from several places in Japan before 2007, but they were on a small scale. In April 2007, N. tapetis appeared suddenly in the commercial bivalve, Ruditapes philippinarum and several other bivalves on the Banzu Tidal Flat in Tokyo Bay. The spread of the parasite was explosive, and caused a mass mortality of the bivalves in the area. Adults of the pycnogonid live freely on or just under the surface of sandy bottoms, and show nocturnal activity. The hatching larva is a typical protonymphon larva. The larva enters the host bivalve, attaches to various soft parts, and feeds on the body fluid of the host. The number of parasites in one host ranges from one to over 60. At least eight different developmental stages can be distinguished in the parasitic larvae and juveniles. Adults leave the host probably just after the maturation molt. The adult male receives one egg-mass onto his ovigers after each mating, and one male can bear up to seven egg-masses. Several experiments were undertaken to attempt to eradicate or reduce the number of N. tapetis, but no effective method has yet been found. Three species of the genus Nymphonella have been described from Japan, the Mediterranean, and southern Africa. They are very similar in morphology, which leads to potential taxonomic confusion.