Ikeda taenioides (Ikeda, 1904) (Annelida: Thalassematidae: Bonelliinae) is the world’s longest spoon worm species, which possesses an extremely long tape-like proboscis with a striped color pattern and a large brownish red trunk. This species is endemic to the Japanese Islands and inhabits a deep vertical burrow in intertidal and subtidal sand flats. Their proboscis, which extends from its small burrow opening, has been frequently observed around Japanese coasts. However, sampling of the main body (i.e., trunk) has been extremely rare because it always stays within a deep part of the burrow. Here, we report the success of the sampling of two specimens of I. taenioides with trunks in two different localities of the Seto Inland Sea (i.e., Ohmishima and Hachi), Japan, in 2019 and 2020 using a yabby pump. This is the first sampling of the trunk of I. taenioides in 88 years after its last collection in Onomichi Bay in 1931. We described the trunk color and morphological characteristics of the two specimens, including the internal anatomy. The trunks of the two specimens showed different colors, that is, pale brown (Ohmishima) and deep brownish red (Hachi). However, they were not distinguished to the species level by the comparison of partial COI sequences, suggesting that I. taenioides has an intraspecific variation in trunk color. Despite the difference in the sampling seasons (Ohmishima: June, Hachi: February), both specimens included numerous ripe eggs. According to previous studies, those collected in November and December also included numerous ripe eggs. Taken together, I. taenioides may be reproductive throughout the year or have multiple reproductive seasons per year.

Distribution and abundance of holothurians before the boom of fisheries in the 1990s were analyzed in relation to types of bottom sediment and biomes in inner reefs of Ishigaki Island, Okinawa, Japan. The data had been collected continuously over three years at Yoshihara and once at three other sites. Fifteen species were found, among which the dominant Holothuria atra and Stichopus chloronotus were abundant on bottoms with sand and seagrass, and those with sand and coral cobbles, respectively. The continuous survey at Yoshihara revealed that the overall density of H. atra was 2 to 3 ind. m⁻², which was the highest among values reported previously, and spatial-temporal distribution of H. atra was almost stable throughout the research period, but the distribution of St. chloronotus fluctuated irregularly. The density of H. atra fluctuated seasonally (high in winter and low in summer) and was correlated negatively with air temperature and irradiation, and positively with cloud cover. The body length of H. atra became longer in summer and shorter in winter. The frequency of asexual reproduction (fission) was estimated at less than 1% of annual recruitment, and the growth rate was estimated to be low (K=0.0845 in von Bertalanffy equation). The high density and slow growth suggested that the H. atra population had reached carrying capacity at Yoshihara. The sand-coated ratio of H. atra was positively correlated with wind speed, however, no trend was found with the spatial-temporal variation in the density and distribution of the sand-coated individuals.

We present a descriptive account of the dynamics of epiphytic diatoms, epifauna, and the leaf surface area of Zostera marina in a shallow water ecosystem. We hypothesized that the growth stage of the host macrophyte (i.e., leaf surface area) influenced the presence of epiflora and epifauna, as well as that the leaf surface area and epifaunal population density affected the cell density and species composition of epiphytic diatoms. To evaluate this hypothesis, we quantified the leaf surface area of a host macrophyte (Zostera marina), the presence of epifauna, and the community of epiphytic diatoms that could be observed on the leaves of Z. marina during the period from May 2017 to December 2018. We conducted a descriptive analysis of the time-series observations of leaf surface area, epiphytic diatom density, and epifauna population density. Epiphytic diatom density was low and epifauna density was high during the growing season of Z. marina. Epiphytic diatom density was high and epifauna density was low during the maturation and senescence periods of Z. marina. Our analysis shows that epifauna densities lagged epiflora densities by at least four months, and that epiflora densities lagged leaf area by four months. Therefore, we hypothesized that herbivorous gastropods and amphipods could alter species composition via their preference of food items (active choice) or by ingesting more of the species that were structurally more available (passive preference).

Carbohydrate-binding modules (CBMs) are non-catalytic protein domains that bind to carbohydrates, and have been well studied in microorganisms. Endogenous CBMs in aquatic invertebrates, however, have not yet been identified, and little is known about their ecological significance to wetland environments. Using an approach of characterizing a recombinant CBM (CjCel9A) from a brackish bivalve, Corbicula japonica, this work identified CjCel9A-CBM’s cellulose-binding activity. Scatchard plot analysis in the study of CjCel9A-CBM binding to α-cellulose showed a high corresponding partitioning coefficient (K_r) of 20.33, indicating CjCel9A-CBM’s high affinity for cellulose. In addition, this affinity tolerated a high ion concentration buffer system, consistent with C. japonica’s adaption to brackish wetland environments. Moreover, immuno-scanning electron microscopy (immuno-SEM) suggested that CjCel9A-CBM binds to α-cellulose unevenly, which was further determined to be caused by its higher affinity for crystalline cellulose (Cellulose I, mostly seen in plant leaves). Together, these findings suggest that CjCel9A-CBM is capable of immobilizing its associated catalytic domain on environmental crystalline cellulose (i.e., fallen leaves) in wetland sediments. Most importantly, they could provide a reasonable answer to a question recognized broadly in wetland ecologists, namely, why many wetland sediments have constant cellulase activities, although the sediments are being washed almost every day.

Holothurians referred to as “teatfish” contain three species, Holothuria (Microthele) nobilis, H. (M.) whitmaei and H. (M.) fuscogilva, that have recently been included in CITES Appendix II for sustainable catch and trade. Taxonomic key traits of these species are primarily genetic sequences and there are few morphological differences among them, except for color patterns of the body. Although located in the northern limit of their distribution, there have been no reports identifying species of teatfish in Japan based on both morphology and genetic traits. This study investigated sequences of mitochondrial cytochrome oxidase subunit I (COI) and morphology including ossicles of black and white teatfish collected from Okinawa Island and Yaeyama Islands, Japan. The entirely black specimens and white specimens having black mottles on the dorsal side were identified as Holothuria (M.) whitmaei and H. (M.) fuscogilva, respectively, based on the agreement of genetic and morphological traits and with published data. There is no clear difference in COI sequences between specimens from Japan and other Pacific regions for both species. The only inconsistent finding with previous reports was that one specimen of H. (M.) whitmaei lacked Cuvierian tubules, which are usually present in this species, implying plasticity of this trait. Mean diameter of the disc and height of the pillars of table ossicles were shorter and longer, respectively, in H. (M.) fuscogilva than in H. (M.) whitmaei (p<0.05, t-test).

The ontogeny of Ilisha elongata was reviewed, and their early distribution was examined because information on the early life history of this species is limited. Revision in ontogeny revealed several unique characteristics to this species, such as two chorions in the egg and a more anterior pelvic bud (fin) position. These characteristics contrast strikingly with the clupeid fishes, suggesting that this species belongs to the Pristigasteridae and not to the Clupeidae. Data from ichthyoplankton collected in March, May, July and November suggest that I. elongata spawned just off river mouths in summer and attained peak spawning in June. The larvae with elliptical eyes migrated inside the rivers, where the waters were more turbid. Thus, the spawning and nursery grounds of I. elongata almost entirely overlapped with those of the clupeid Sardinella zunasi both temporally and spatially, which may result in larval competition between the two species.

Mastigias papua, known as the golden (or spotted) jellyfish, is an epipelagic jellyfish widely distributed in the warm waters of the West Pacific. This jellyfish has a brownish body, owing to zooxanthellae, and white spots. We measured the maximum force to pierce the umbrella, which averaged 94–144 mm in diameter, to evaluate the hardness of M. papua, and returned a range of 0.14–0.45 N. Correlation analyses indicate that when the M. papua medusa grows (i.e., becomes heavier), the umbrella becomes larger in diameter, as well as thicker and harder within the size range we examined. However, a significant relationship between the hardness of the umbrellar apex and the thickness of the umbrella was not obtained. White spots are comprised of loose aggregates of mesogleal cells containing reflective granules. Since the white spots and the transparent parts were not significantly different in hardness, the spots were unlikely to strengthen the umbrella. The primary function of the spots may be the shading of solar radiation. Most of the zooxanthellae are located in mesogleal cells, and often beneath the exumbrellar epidermis. Therefore, light shading by white spots may be unnecessary for the zooxanthellae in mesogleal cells.

More than 100 individuals of sea cucumber larvae were collected in the Japanese coastal sea of Moroiso, Sagami Bay, Kanagawa Prefecture, central-eastern Japan, in January 2018. Based on an obtained sequence of mitochondrial 16S rRNA gene region of one juvenile, it was identified as Sclerodactyla multipes by BLAST search with 0.3% genetic distance. The developmental process of the S. multipes was observed for three months, in which time, they grew from 250 µm to about 4 mm in length; here they showed distinct tentacles and dermal ossicles. Detailed morphological features of this species were described based on stereomicroscopic, fluorescence and SEM observations for the first time. This is the first description of life history through planktonic larva to juveniles in the family Sclerodactylidae.