In the second part of a review of the genus Fusinus in Japan, several species commonly confused or associated with F. undatus (Gmelin, 1791) and F. similis (Baird, 1873) are examined via their types and material from various collections. F. undatus and F. similis have been frequently confused in literature, but are here shown to be separate species. F. similis is further compared with the types and other examples of the morphologically similar F. galatheae Powell, 1967, F. bountyi Rehder & Wilson, 1975 and F. genticus (Iredale, 1936). In addition, F. sandvichensis (Sowerby III, 1880), F. michaelrodgersi Goodwin, 2001 and R midwayensis Kosuge, 1979 are illustrated for comparison. The new species Fusinus mauiensis is described from Hawaii, where it is apparently endemic to the island of Maui. Lectotypes are selected for Fusinus undatus, F. similis and F. sandvichensis.
In the Ryukyu Islands, Japan, Litigiella pacifica n. sp. lives attached to the body of the burrowing sipunculan Sipunculus nudus. The morphology of the shell and the soft parts are described and compared with other bivalve commensal with the same sipunculan. The new species is hermaphroditic, and the filamentous sperm cells are stored in paired seminal receptacles.
The tropical mussel Modiolus philippinarum is common and abundant in seagrass beds in Okinawa Island, southernmost Japan, and is commercially important to local fishermen. In order to elucidate the mechanisms that maintain the difference in density between benthic populations of the mussel within and outside seagrass beds, we monitored temporal variations in densities of the mussel at different developmental stages (planktonic larvae; new settlers; small and large individuals) within and outside seagrass beds in Okinawa Island over one year. Based on these data, the difference in larval density was not significant, but there were significant differences between densities of new settlers (shell length<250μm), small individuals (250μm≦shell length<1.0mm) and large individuals (shell length≧1.0mm), within and outside seagrass beds. Cohort separation was applied to data for shell length distributions of new settlers and small and large individuals, and revealed that larvae mainly settled in July to August. New settlers grew up to about 20 mm in shell length in their first year; their mortality was constant and/or low once individuals had attained shell lengths of about 300μm. These facts indicates that the much higher density of benthic populations of the mussel within seagrass beds may be determined at and/or shortly following larval settlement, though details of the mechanisms driving the above difference are not yet identified.
The reproductive behavior of the Japanese spineless cuttlefish Sepiella japonica was observed in a tank. The males competed for females before egg-laying and then formed pairs with females. The male then initiated mating by pouncing on the female head, and maintained the male superior head-to-head position during the mating. Before ejaculation, the male moved his right (non-hectocotylized) arm IV under the ventral portion of the female buccal membrane, resulting in the dropping of parts of spermatangia placed there during previous matings. After the sperm removal behavior, the male held spermatophores ejected through his funnel with the base of hectocotylized left arm IV and transferred them to the female buccal area. The spermatophore transfer occurred only once during each mating. The female laid an egg capsule at average intervals of 1.5 min and produced from 36 to more than 408 egg capsules in succession during a single egg-laying bout. Our results also suggested one female produced nearly 200 fertilized eggs without additional mating, implying that the female have potential capacity to store and use active sperm properly. The male continued to guard the spawning female after mating (range=41.8-430.1 min), and repeated matings occurred at an average interval of 70.8 min during the mate guarding. Although the time spent on the sperm removal in S. japonica was shorter than in other sperm-removing cuttlefishes, the shorter sperm removal duration may be compensated by the post-copulatory mate guarding and repeated matings in this species.
In recent years, the volume of the Japanese short neck clam Ruditapes philippinarum imported from China, South Korea and North Korea has increased rapidly to compensate for the decrease in domestic production in Japan. Imported clams are generally released in areas already inhabited by the same species, and it is feared that they may affect the domestic populations. It is necessary to understand the genetic characteristic of the various local populations to manage and conserve biodiversity. However, the genetic variation of the Japanese short neck clam from Japan and the other countries has not been studied. This study was therefore designed to analyze the genetic variation among local populations from Japan and China using nucleotide sequence of the M and F types COX1 gene from the mtDNA of Japanese short neck clam. The nucleotide sequence for the total length of the M-type (1608 bp) and F-type (1599 bp) COX1 gene of 39 male individuals collected during the spawning season (November to May, 2004) from nine locations in Japan and China was determined. In the M-type COX1 gene, the number of nucleotide and amino acid substitutions were higher than in the F-type COX1 gene. Both the M-type and F-type COX1 gene revealed differences in nucleotide sequence between Japanese and Chinese populations, which were clearly grouped in the phylogenetic trees (MP and NJ methods). In addition, the Japanese populations were divided into two subgroups by the M-type COX1 gene, the Honshu-Kyushu (Tokyo Bay, Mikawa Bay, Nanao Bay, Miyazu Bay and Ariake Sea) and Hokkaido (Notsuke Bay) groups. The Chinese populations were also divided into two subgroups, these from the North (Dalian Bay and Kiachow Bay) and those from the South (Xiamen Bay).
Two genetic types (A and B) of Anodonta "woodiana" were identified as A. lauta and A. japonica respectively, based on the number of large teeth on the hook of glochidia, which was always more than 12 in A. lauta, but less than 11 in A. japonica on the average. The ratio of shell height to shell length in the glochidia was not a suitable character to identify these two species, because it varied largely in A. japonica.
To reveal the mechanism of androgenesis, we observed chromosomes, centrosomes and microtubules in fertilized C. fluminea eggs from meiosis to first mitosis. We also observed fertilized eggs of C. sandai, in which development is normal. In C. sandai, one of the centrosomes attached to the egg cortex and the other remained in the center of eggs at metaphase of meiosis. The spindle axis at metaphase of meiosis was perpendicular to the egg cortex. On the other hand, in androgenetic eggs of C. fluminea, two centrosomes attached to the egg cortex. The spindle axis was parallel to the egg cortex. As a result, all egg chromosomes were extruded with two polar bodies at first meiosis. Only the male pronucleus remained in eggs after the polar body formation. C. fluminea has two centrosome attachment sites, while C. sandai has only one attachment site at meiosis. We deduced that the change of attachment site may cause the androgenesis in C. fluminea. We also measured the size of male pronucleus in C. sandai and C. fluminea fertilized eggs during meiosis. At 20 min after fertilization, all egg chromosomes were extruded with two polar bodies in C. fluminea. Meiosis of C. fluminea was apparently completed at 20 min, but the male pronucleus didn't enlarge until 40 min had elapsed. At 40 min, the male pronucleus started to enlarge, which coincides with the period of second polar body formation in C. sandai. We suggest that the cell cycle of second meiosis is still functional in oocytes of C. fluminea.
A camaenid land snail that has previously been cited in literature as "Satsuma (Satsuma) peculiaris lepidophora Kuroda MS" (Yamashita et al, 1990) or "Satsuma (Satsuma) japonica lepidophora Kuroda MS" (Ohara & Otani, 2002), inhabits a small islet called "Oshima" (Fig. 1), located about 5 km south off Kii-Nagashima, Kihoku-cho in the southern Mie Prefecture. It has hitherto been known from four specimens in museum collections; two in the Kuroda Collection in Nishinomiya Shell Museum, and two in the Kawamura Collection in the National Science Museum, Tokyo. In order to clarify the taxonomic status of this snail, the author carried out two field samplings on the islet in 2002 and 2004, with the permission of the Agency for Cultural Affairs, Japanese Government, and collected seven live specimens. Careful examination of this material, together with additional specimens collected by Mr. Masaru Naka, revealed that it is a distinct new species, and the description is given in the following lines.
The shipworm Zachsia zenkewitschi Bulatoff & Rjabtschikoff, 1933 lives inside the rhizomes of the eelgrasses Phyllospadix and Zostera (Helobiales; Zosteraceae) and has sporadic distribution records from Primorskii Krai (=Primoriye Region) to Siberia in the Russian Far East and in Japanese waters (Higo et al, 1999). Its detailed distribution and habitats have been surveyed in detail only locally along the coast of Vladivostok in Primoriye (Turner et al, 1983; Fig. IF). In Japanese waters, this species has been recorded in only three catalogues of local molluscan faunas (Fig. 1; Inaba, 1982; Kano, 1981; Kuroda & Habe, 1981). These catalogues, however, did not provide information on detailed collecting sites and habitats. This rare species was recently rediscovered along the coast of Miyagi Prefecture, northeast Japan (Sasaki et al, 2006; Fig. 1C). Z. zenkewitschi has dwarf males and exhibits remarkable sexual dimorphism. Bulatoff & Rjabtschikoff (1933) noted the presence of larvae' within the female body with a long tail-like appendage and an internal shell. Turner & Yakovlev (1983) confirmed that the larvae' are dwarf males, a rare example of sexual dimorphism in bivalves. Subsequent authors studied the biology of Z. zenkewitschi in detail and determined that: 1) spawning occurs 2-5 times in summer; 2) fertilization then takes place in the suprabranchial cavity of the female using sperm received from the dwarfmales; 3) after fertilization, the larvae are brooded until they grow to the straight-hinge stage; 4) the released larvae settle on the rhizomes of the eelgrass after a short planktonic stage; and 5) the larvae either crawl into the lateral pouches of a female within the rhizome and grow into dwarf males or develop into females in cases where the rhizomes are free from any adult female (Drozdov et al, 1999; Turner et al, 1983; Yakovlev et al, 1998). However, it is still not yet known how this species dispersed so widely despite its short-term, free-swimming larval stage. Turner & Yakovlev (1983) observed that the larvae swam mostly near the bottom of a culture dish in their laboratory. They hypothesized that in natural environments the larvae can swim only for short distances within the eelgrass beds and that wide dispersal might have been achieved through long-distance transportation of the host eelgrass by accidental drifting. However, this hypothesis has not been verified to date. This report is the first documentation of Z. zenkewitschi in drifted rhizomes of eelgrass, and describes the soft animal morphology of this species.