We found a new species of tellinoidean bivalve in coral reef lagoons of the Ryukyu Archipelago, Japan. The lagoons were dominated by the seagrass Halophila ovalis. The new bivalve is minute and slightly inequivalve; the shells are extremely flattened; there are unique hinge teeth with a developed, vertically oriented resilium and vestigial external ligament; commarginal lamellae are widely spaced and sharp; inhalant and exhalant siphons are elongated; inner and outer demibranchs are triangular. We here name the new species Semelangulus lacrimadugongi. Definitive familial placement awaits further revision of related genera in the Tellinidae and Semelidae. The known habitats of this bivalve are the remaining areas in which dugongs survive, or have survived until recently.
Following analytical studies on the two forms (Japanese names: Awaji-chihiro and Yami-no-nishiki) of Volachlamys hirasei, fossil specimens in genus Volachlamys from Japan were examined. The fossil specimens were from the Kazusa Formation (1.7 Ma), the Kitaarima Formation (0.9 Ma), the "Maiko Shell-Beds" (Early-Middle Pleistocene), the Takatsukayama Formation (0.41 Ma), the Atsumi Group (0.44 Ma), the Kioroshi Formation (0.125 Ma) and a seaside alluvium in Takamatsu (0.006 Ma). In addition to these, Recent specimens collected from the Seto Inland Sea were examined. Shells of the specimens were measured, and growth was analyzed by observing the annuli on the shell surfaces. In the fossil specimens, the Yami-no-nishiki form was detected in the Atsumi, Kioroshi and Takamatsu samples; it appeared in 1 of 44 individuals in the Atsumi sample, 1 of 2 individuals in the Kioroshi sample, and 17 of 39 individuals in the Takamatsu sample. The remaining specimens were comprised entirely of the Awaji-chihiro form, suggesting that the Yami-no-nishiki form first appeared around the middle Pleistocene. Morphologically, although shell proportions and costae number were unique by locality, there were no samples that were particularly specialized. On the other hand, the shell weight index (SWI) of the Maiko sample was prominently lower, indicating that these shells were much thinner and lighter than the other specimens. The growth analysis revealed distinctly greater growth in the Maiko specimens, although the other specimens (including the Recent ones) showed similar growth rates to one another. These results suggest that only the Maiko specimens were genealogically distinct from the others. The fossil specimens of Volachlamys from Japan were generally supposed to be Volachlamys yagurai, being treated as a species distinct from V. hirasei. The specimens from the "Maiko Shell-Beds", which is the type locality of V. yagurai, have biological characteristics so different from those of the Recent specimens that they are treated as a distinct species; however, in the other fossil specimens, significant characteristics that differ from those of the Recent specimens of V. hirasei could not be detected. These results indicate that only the fossil individuals from the "Maiko Shell-Beds" are referable to Volachlamys yagurai, and those from all other localities should be assigned to Volachlamys hirasei, which is common to the Recent specimens.
Juvenile specimens of two scaphopod species with the protoconch intact were collected from Wakayama Prefecture, Japan. One has a hexagonal cross-section with six longitudinal keels and is identified as Dentalium octangulatum; the other is of an unidentified species. Dentalium octangulatum differs from other known species in having a smaller protoconch A and an extremely long protoconch B. The protoconch of the unidentified species matches the type 1 protoconch of Dentaliida. The differences in protoconch morphology may reflect those in larval ecology, but this hypothesis should be tested by developmental studies.
A fossil Ellobium is recorded for the first time from the uppermost Lower Miocene Tate Sandstone Member of the Kadonosawa Formation in Iwate Prefecture, northeastern Honshu, Japan. The Tate species is comparable with the Recent Ellobium aurisjudae (Linnaeus) living in Indo-Pacific mangrove swamps. This is the northernmost record of the genus in East Asia through the Cenozoic. The occurrence of Ellobium in the member is regarded as new evidence for the presence of mangrove swamps in northeastern Honshu in the latest Early Miocene age.
Size-related differences in the day/night activity pattern and habitat preference of the herbivorous snail Gibbula umbilicaris (Gastropoda: Trochidae) on Posidonia oceanica leaves were investigated by a laboratory experiment. Snails were sampled at Ischia Island (Gulf of Naples) from a depth of 3 m, in December 1995. Some snails of three different size classes were individually placed in an aquarium and offered two types of differently epiphytized P. oceanica leaf fragments . Four types of behavior (rest, shaking epipodial tentacles without any other motion, directional movements, and shell twisting mainly for foraging) were recorded. Large sized snails showed a particularly high activity at night and were mostly inactive during the day, but this clear day/night pattern became weaker with decreasing snail size. However, by summing up the data for a 24-hour cycle, the relative proportion of the different behavioral types is similar for all size classes. Small sized snails utilized the two types of leaf without preferences, while larger sized snails mainly foraged on the apical, more epiphytized parts of the leaves. In the presence of the sea urchin Paracentrotus lividus, only the small sized snails changed their behavior, becoming more active in feeding.
The ovary and associated appendages of the rare epipelagic octopus, Ocythoe tuberculata caught alive near the harbor of Naoetsu Port, Sea of Japan on 15 February 2005, were examined histologically. The ovary was 40 g in weight, and contained approximately 60,000 eggs. The oocytes, in variously developmental stages, were attached singly to lamella-like stalks. The ovary possesed a central cystic coele, with a complex labyrinthine form in cross section. Each ovoid oocyte in the early stage had a prominent round nucleus (= germinal vesicle) containing several nucleoli. Numerous oocytes were surrounded by an intricately folded follicular epithelial layer. Large spherical oocytes had significant yolk accumulation. Deeply infolded mucosae were present in the proximal part of the oviduct, whereas shallowly intricate mucosae were detected in the distal part of the oviduct, which was surrounded by thick muscular and fibrous connective tissues. The shape of the oocytes and pattern of oogenesis of this epipelagic octopus were similar to those of coastal and deep-sea octopods.
Glochidia and juveniles of two species of Margaritifera were examined in the Sakasa River at Togakushi, Nagano Prefecture, and four other localities in Japan. The shape and size of the glochidia were similar in both species, but the surface sculpture of the glochidial shell was different: smoother in M. laevis and rougher in M. togakushiensis. On the other hand, juveniles were oblong and flat in M. laevis, but ovate and inflated in M. togakushiensis. Most of them could be consistently separated using a discriminant function estimated from the shell length and shell height. Juveniles obtained in the other four localities were also identified with one or the other species by using the discriminant function. About 40 days after infection, the glochidia metamorphosed into juveniles on the host and the discriminant function is also applicable to the parasitic juveniles.
A shell collected in July 1988 was brought to my attention several years ago. Since then no other similar material has been found, and attempts to obtain more material remained unsuccessful. This is probably due to the locality, which is far away from usual field trip localities. However, the particular spiral cord morphology and the unusual pattern of the varical fronds separate this species definitively from any other known form of Triplex. The terminology used here to describe the spiral cord morphology is based on the standard terminology established by Merle (1999, 2001) for each major sequence of appearance of the primary and secondary cords.
The family Turridae is highly diverse in most world oceans from shallow to deep waters and from high to low latitude (Tucker, 2004). Even within Japan, at least 394 species have been recorded (Higo et al, 1999: G3479-3872), and we frequently encounter undescribed or unidentified specimens. It is highly likely that the diversity of the family in Japan is not adequately reflected in the literature. The genus Aliceia Dautzenberg & Fischer, 1897 is poorly known. There are only two described species in the world, both of small size. Aliceia aenigmatica Dautzenberg & Fischer, 1897 has been recorded from bathyal depths (1800-1980 m) in the Azores (Bouchet & Waren, 1980: 91), and Aliceia simplicissima (Thiele, 1925) was collected from off Indonesia and Zanzibar at depths of 356-470 m (Sysoev, 1997: 345, fig. 57). A possible third species (Bouchet & Waren, 1980: 90) was represented by an unidentified specimen reported by Kay (1979: 364, fig. 115N) from a depth of 700 m off Lanai, Hawaii as "Thatcheriasyrinx sp." During a series of dredge survey off Ogasawara Islands, southern Japan, the first author collected a previously unknown species of Aliceia. This paper describes this interesting new species.
The genus Panacea is a member of the Pholadomyoidea and comprises just six rare species in the world (Coan, 2000). In the Indo-Pacific region and adjacent areas, there are only three known species in the genus: P. sumatrana Thiele & Jackel, 1931 from Indonesia (175 m deep), P. tasmanica (Hedley & May, 1914) from Tasmania, southern Australia (91 m deep) and P. chilensis Coan, 2000 from Chile (130-180 m) (Coan, 2000). During a research cruise by the R/V Tansei-Maru, the first author (TS) collected a single valve of an unknown species of Panacea. We describe this species here as the first reliable record of the genus from Japan.
Yagura's scallop, Volachlamys yagurai (Makiyama, 1923), is a Pleistocene pectinid species from Japan. It was described as Pecten yagurai by Makiyama (1923) on the basis of "Pliocene" specimens from Maiko, Hyogo Prefecture. Prior to this publication, "Pecten yagurai Makiyama" was briefly introduced by Yagura (1922) for the same taxon from the same locality. The latter was intended to be published after Makiyama (1923), because Yagura (1922) noted "Pecten Yagurai was described as a new species by Mr. Jiro Makiyama, Kyoto Imperial University, in September, 1922". P. yagurai Yagura, 1922 is regarded as the earliest available name, because it was accompanied by photographs as an indication of new status (ICZN Art. 12.2.7). Consequently, Pecten yagurai Makiyama, 1923 is regarded as a junior synonym and a junior homonym of Pecten yagurai Yagura, 1922. Lectotypes of both taxa are designated herein for the fixation of the taxonomical confusion.