著者

Shuhei Ikeda Ayaka Hashimoto Kazuya Okuizumi

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.18, no.3, pp.160-166, 2023-08-31 (Released:2023-08-31)

参考文献数

22

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This study reports an effective and simple method for culturing the comb jellyfish, Beroe cucumis. The method for breeding another comb jelly, Bolinopsis mikado, was published by Ikeda et al. (2022), in which Bolinopsis mikado was bred stably and in large numbers, and then provided as food to developing Beroe cucumis. Fertilized eggs were found in a 235-L tank two days after five parental Beroe cucumis were housed in the tank, and the parental individuals were isolated from the tank the next day. The day after the eggs were found, Beroe cucumis larvae (0.54 ± 0.04 mm long (n = 9)) were observed in the tank daily and were fed Bolinopsis mikado. The Beroe cucumis larvae were only fed Bolinopsis mikado during the early stages of development. They reached a total length of approximately 10 mm in 17 days, and by day 20, when most had grown large (approximately 12 mm and over) enough to not pass through the 3-mm perforated plates, they were moved to a 145-L display tank. Thereafter, they were reared in the same manner and were successfully propagated cumulatively for more than five generations. The greatest advantage of this culture method is that the larvae need only be fed and observed until they reach the size required for display. Therefore, stable breeding of Beroe cucumis can be achieved by feeding its larvae with Bolinopsis mikado, reducing labor and stress on the organisms from frequent water changes.

著者

Michael Ford Nicholas Bezio Allen Collins

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.15, no.4, pp.296-305, 2020-11-18 (Released:2020-11-12)

参考文献数

36

被引用文献数

2 10

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On April 10, 2015, three individuals of an undescribed species of ctenophore were observed moving just above the seafloor in the Arecibo Amphitheater inside the Guajataca Canyon, north-northwest of Puerto Rico at a depth of approximately 3,900 m. The ctenophore is distinctive; having two prominent tentacle arms, a body that is rectangular when observed laterally along the tentacular plane, and rounded when observed laterally along the stomodeal plane. The tentacle arms each give rise to an extensible tentacle bearing short tentilla of uniform length and distribution. One ctenophore appeared to be anchored to the seafloor by its two long flexible tentacles, as well as by two filaments exiting its oral end. The overall form of the ctenophore suggests classification within the problematic, non-monophyletic order Cydippida, but the robust tentacle arms are more reminiscent of benthic species of Platyctenida, particularly those of families Lyroctenidae and Ctenoplanidae. Whereas most platyctenid ctenophores do not possess ctene rows in their adult forms, features that are possessed by the new species described herein, species of Ctenoplanidae retain comb rows as adults and are capable of limited swimming. The species described herein is easily distinguishable from all other known species of Ctenophora and may trace its origin to a lineage diverging near the origin of Platyctenida.

著者

Hiroki Nakajima Ryuta Yoshida Tohru Naruse

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.17, no.1, pp.34-44, 2022-02-22 (Released:2022-02-23)

参考文献数

30

被引用文献数

2

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Four mantis shrimp species are recorded from the Ryukyu and Ogasawara islands, southern Japan: Gonodactylaceus ternatensis (De Man, 1902) (Gonodactylidae); Lysiosquilloides siamensis (Naiyanetr, 1980) (Lysiosquillidae); Alimopsoides tuberculatus Moosa, 1991 (Squillidae); and Busquilla plantei Manning, 1978 (Squillidae). This is the first specimen-based record of G. ternatensis and the first distributional records of the latter three species from Japan. The genus Lysiosquilloides Manning, 1977 is recorded for the first time from Japanese waters, and the genus Alimopsoides Moosa, 1991 is newly found from the northern hemisphere. Diagnoses, taxonomic remarks, ecological notes and new standard Japanese names are provided.

著者

Ryutaro Goto Yumi Henmi Yuto Shiozaki Gyo Itani

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.16, no.3, pp.155-164, 2021-08-06 (Released:2021-07-31)

参考文献数

42

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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.

著者

Takahiro Sugiyama Naoto Jimi Ryutaro Goto

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.15, no.4, pp.289-295, 2020-11-18 (Released:2020-11-12)

参考文献数

30

被引用文献数

6

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The Polynoidae, commonly known as “scale-worms” due to the scale-like elytra on the dorsal surface, contains many species living in symbioses with other invertebrates. Most of these symbionts are host-specific, but some have a wide range of hosts. The genus Asterophilia includes two species living in shallow subtropical to tropical waters in the Pacific Ocean as ectosymbionts of asteroids and, more rarely, crinoids. Here, we recorded Asterophilia culcitae from asteroid hosts (Culcita novaeguineae, Linckia laevigata, L. guildingi, and Leiaster leachi) and, for the first time, from holothurian hosts [Stichopus chloronotus, Holothuria atra, H. (Stauropora) pervicax, and Bohadschia argus] along warm Japanese Pacific coasts. The cytochrome c oxidase subunit I sequences of the specimens from holothurians did not differ significantly from those on asteroid hosts, proving that A. culcitae has a wide host range across three different echinoderm classes: asteroids, holothurians, and crinoids. The general body color of A. culcitae was constantly reddish (female) or whitish (male), regardless of the host body color, although a previous study suggested that it differs in accordance with the host body color. However, we found that one individual from a holothurian host showed a different color pattern: A. culcitae typically shows three whitish or yellowish elytral mounds that have been suggested to mimic the tube foot of the asteroid hosts, whereas one individual from S. chloronotus had reddish brown translucent mounds, which we suggest might be cryptic on its holothurian host.

著者

Ryutaro Goto Taigi Sato

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.16, no.1, pp.69-72, 2021-02-19 (Released:2021-02-19)

参考文献数

21

被引用文献数

3

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The family Vitrinellidae is a group of tiny marine snails that generally occur in shallow waters of temperate and tropical seas. The biology of most vitrinellid species remains poorly understood. In this study, we report that Circulus cinguliferus (A. Adams, 1850) (Vitrinellidae), distributed widely in the warm shallow waters of the Pacific, inhabit crustacean burrows, including those of the mud shrimp Neaxius acanthus (Strahlaxiidae) and snapping shrimp Alpheus rapax (Alpheidae), in the intertidal and subtidal flats of the Okinawa Islands, southern Japan. They exhibited highly clumped distribution among the host burrows, suggesting that they are attracted by conspecifics. Although the biology of most Circulus species remains unknown, Circulus texanus (D. R. Moore, 1965) is known to inhabit stomatopod burrows in the western Atlantic. Our findings suggest that such a commensal habit may be more widespread in this genus than previously thought.

著者

Sho Toshino Jun Nishikawa Khwanruan Srinui Supattra Taleb Hiroshi Miyake

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.14, no.3, pp.143-149, 2019-08-26 (Released:2019-08-17)

参考文献数

29

被引用文献数

2

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The stings of box jellyfishes can be fatal, so knowing the fauna of a certain area is important to save lives. Five described and two still-undescribed species of Cubozoa have been reported from Thailand: Chironex indrasaksajiae, Chironex sp., Chiropsella sp., Chiropsoides buitendijki, Copula sivickisi, Morbakka fenneri, and Tripedalia cystophora. We made detailed observations of the morphology of two of the species newly recorded in Thailand: Alatina morandinii and Tripedalia binata. The molecular phylogeny of these species is also discussed. Additional investigations are needed to understand the diversity of Cubozoa in Thailand.

著者

Hisanori Kohtsuka Kohei Oguchi Yusuke Yamana Masanori Okanishi

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.16, no.3, pp.228-236, 2021-08-06 (Released:2021-07-31)

参考文献数

60

被引用文献数

1

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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.

著者

Luna Yamamori Makoto Kato

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.14, no.2, pp.131-134, 2019-05-28 (Released:2019-05-24)

参考文献数

13

被引用文献数

2

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The rock-boring sea urchin, Echinostrephus molaris, excavates soft rocks, and the pits are later used by non-boring sea urchins such as Echinometra mathaei and Anthocidaris crassispina. The pits used by these non-boring sea urchins are also characteristically inhabited by a limpet-like algivorous trochid snail, Broderipia iridescens (Gastropoda, Trochidae). To determine how this unique symbiotic association is maintained, we observed reproduction and larval development of the snail, and performed assays to detect what induced settlement in the snail larvae. As candidates of settlement inducers, a habitat biofilm plate, the host and the non-host sea urchins, and conspecific snails were kept in separate glass bowls, and newly hatched B. iridescens veliger larvae were introduced to each bowl. Sixty to 80% of larvae settled in bowls that contained the non-boring host sea urchins and conspecific snails. On the other hand, only approximately 8% of the larvae settled in bowls containing the boring non-host sea urchins. This is the first report demonstrating that larval settlement of an algivore is induced not by the habitat biofilms, but by the symbiotic hosts.

著者

Shuhei Ikeda Chika Sato Michiko Yamaguchi Hibiki Kanno Kazuya Okuizumi

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.17, no.4, pp.343-348, 2022-11-30 (Released:2022-11-30)

参考文献数

19

被引用文献数

2

---

This paper reports an effective and easy method to culture the ctenophore Bolinopsis mikado. Fifteen adult B. mikado individuals were maintained in a kreisel tank, and fertilized eggs, which were detected in the following days, were all raised together in the same tank. From the early development stage to day 13, the B. mikado cydippid larvae were only fed Artemia nauplii. The cydippid larvae were able to easily catch the Artemia nauplii excreted by adult B. mikado; therefore, they were considered capable of growing on excrement. Adult B. mikado individuals were removed from the tank when the cydippid larvae reached approximately 5 mm in length (day 14). The cydippid larvae were then transferred to a circular tank with a water spray chamber. Approximately 21 days after the early development stage, cydippid larvae had grown to lengths of approximately 20 mm and were then bred in the same manner up to the 5th generation. The greatest advantages of this culture method are that it is less cumbersome and only requires feeding and observation until the cydippid larvae attain a size that enables them to pursue live Artemia nauplii. Thus, damage to the living body due to water exchange and the labor involved are reduced, thereby allowing stable breeding of B. mikado.

著者

Avril H. Underwood Ilka Straehler-Pohl Teresa J. Carrette Jessica Sleeman Jamie E. Seymour

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.13, no.4, pp.143-153, 2018-11-21 (Released:2018-11-14)

参考文献数

71

被引用文献数

4

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This research presents the early life history stages of Malo maxima, a recently described tropical Australian cubozoan from the family Carukiidae, from sexual fertilisation to metamorphosis including planula, polyp, asexual reproductive strategies and young medusa. We discuss the similarities between M. maxima and two closely related carukiid species from Japan and Australia including morphology and behaviours previously undocumented in the class Cubozoa. All three carukiids can reproduce by mono-disk strobilation, a strategy common to all other orders of the class Scyphozoa but only recently described in Cubozoa.

著者

Chong Chen Leigh Marsh Jonathan T. Copley

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.13, no.1, pp.25-27, 2018-02-28 (Released:2018-03-14)

参考文献数

16

被引用文献数

5

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“Mating stacks” have been widely documented in calyptraeid slipper limpets, which are protandric and exhibit sequential hermaphroditism. Gigantopelta is a genus of peltospirid snails endemic to deep-sea hydrothermal vents containing two species, one distributed on the East Scotia Ridge in the Southern Ocean and another on the Southwest Indian Ridge in the Indian Ocean. Here, we report the observation that both species form extensive (often >15 individuals) “snail chains”. These chains are potentially analogous to ‘mating stacks’ of calyptraeids, or alternatively, maybe a behaviour to facilitate spermatophore transfer. Both Gigantopelta species apparently have separate sexes and are sexually mature at a small size. However, it remains unclear whether they undergo sex change during their life.

著者

James Davis Reimer Chloé Julie Loïs Fourreau Takuma Fujii Yuji Ise Yuka Kushida Iori Mizukami Megumi Nakano

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.17, no.3, pp.249-254, 2022-08-30 (Released:2022-08-30)

参考文献数

13

被引用文献数

3

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We report the presence of the coral-killing sponge species Chalinula nematifera (de Laubenfels, 1954) in southern Japan via photographic records and specimens. The species appears to be a substrate generalist on scleractinians and occasionally octocorals, and is found across a wide variety of depths (0 to 24 m), as has been recently reported for this species from Indonesia. From our information, the species is found in southern Japan across the southern and central Ryukyu Islands, with a northern limit of Amami-Oshima Island, although future work will likely expand the range. As our records stretch back more than 20 years, we do not believe Chalinula nematifera is a recent arrival to the region. Due to the potential for this species to harm coral reefs, we suggest field surveys are needed to establish a baseline distribution and abundance database to aid in future monitoring.

著者

Sho Toshino

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.15, no.4, pp.327-333, 2020-11-18 (Released:2020-11-12)

参考文献数

34

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The order Coronatae is a unique group, with the following characters distinguishing them from other scyphozoans: a coronal furrow, a coronate pedalium, and oocytes that develop without accessory pigments. Coronatae polyps are enclosed in chitinous tubes and produce multiple ephyrae via polydisk strobilation. So far, eleven described species of Coronatae have been reported in Japanese waters: Atolla wyvillei, Atolla vanhoeffeni, Atolla russelli, Atorella vanhoeffeni, Atorella japonica, Nausithoe punctata, Palephyra pelagica, Periphylla periphylla, Periphyllopsis braueri, Stephanoscyphistoma corniformis and Nausithoe racemosa. The present study reports detailed observations of the morphology of one species newly recorded in Japan: Linuche draco. Development from ephyra to mature medusa was observed and recorded. Additional investigations are needed to understand the diversity of the order Coronatae in Japan.

著者

Aoi Tsuyuki Hisanori Kohtsuka Natsumi Hookabe Hiroshi Kajihara

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.17, no.2, pp.147-155, 2022-05-30 (Released:2022-05-31)

参考文献数

26

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The cotylean polyclad flatworm Bulaceros porcellanus Newman & Cannon, 1996 has so far only been recorded in a few tropical locations in the Indo-Pacific Ocean, including the Lakshadweep Islands (India), the Great Barrier Reef (Australia), and the Marshall Islands (Republic of the Marshall Islands). In this study, we report B. porcellanus for the first time from Japanese waters based on specimens collected in Misaki (Kanagawa) along the Pacific coast of Honshu. This new record expands the species’ known geographic distribution northward to include the warm temperate region of Japan. Our molecular phylogenetic analysis revealed that B. porcellanus formed a clade with Pseudoceros harrisi Bolaños, Quiroga & Litvaitis, 2007, and was separated from the monophyletic group composed of 19 other species of Pseudoceros Lang, 1884, including its type species Proceros velutinus Blanchard, 1847 (now Pseudoceros velutinus). Based on the morphological and phylogenetic closeness between P. harrisi and B. porcellanus (type species of Bulaceros Newman & Cannon, 1996), we transfer P. harrisi into Bulaceros with a revision of the diagnosis of Bulaceros.

著者

Natasha Phillips Lawrence Eagling Chris Harrod Neil Reid Valentina Cappanera Jonathan Houghton

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.12, no.2, pp.143-144, 2017-05-30 (Released:2017-06-06)

参考文献数

19

被引用文献数

10 16

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This study presents new evidence of the extensive trophic role of gelatinous zooplankton by documenting typically non-marine predators, mallard ducks, feeding on hydrozoans in shallow, coastal environments.

著者

SAWAMOTO SHOZO MATSUMOTO RUI

出版者

日本プランクトン学会、日本ベントス学会

雑誌

Plankton & benthos research (ISSN:18808247)

巻号頁・発行日

vol.7, no.4, pp.203-206, 2012-11-01

被引用文献数

14

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More than 50 specimens of the megamouth shark Megachasma pelagios have been reported so far, but biological observations on the species are still limited. We examined a female megamouth specimen that was captured by the bonito purse seine fishery in the Kuroshio Extension in July 2007 and donated to the Okinawa Churaumi Aquarium. The specimen was an immature female, 3,667 mm in total length and 361 kg in weight. The stomach contents measured 2,200 mL excluding the portion that was lost from the specimen before measurement. Detailed examination of a small part (14.6 mL) of the stomach contents revealed undamaged worm-like organisms, 10 partially damaged euphausiids and abundant fragmented pieces of euphausiids. The worm-like organisms were probably parasites such as tapeworms. The partially damaged euphausiids were identified as Euphausia pacifica except for one individual of Nematoscelis difficilis. Based on the number of fragmented right mandibles, which were less damaged than the other fragmented appendages, the total number of euphausiids in the stomach contents is estimated to be at least 18,000 individuals. The high abundance of euphausiids in the stomach contents suggests that the present specimen has fed on a swarm of E. pacifica in an oceanic area.

著者

Yusuke Kondo Shoma Okada Susumu Ohtsuka Takeshi Hirabayashi Aya Adachi Makoto Urata Sho Toshino Hiroshi Miyake Nanako O. Ogawa Naohiko Ohkouchi

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.13, no.2, pp.66-74, 2018-05-30 (Released:2018-05-24)

参考文献数

50

被引用文献数

1 1

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In this study, we investigated the trophic interactions between the Japanese giant box jellyfish, Morbakka virulenta, and fish in the central part of the Seto Inland Sea, western Japan, in autumn and winter. Occurring in the surface waters at nighttime, these cubomedusae, regardless of their size (1.5 to 22.5 cm in bell height), were found to be piscivorous, feeding mainly on the Japanese anchovy, as shown by their stomach contents analysis. This finding was supported by a stable isotopic analysis and by an unchanged cnidome, irrespective of the bell height of medusae. Their nocturnal occurrence near the surface often took place around the slack tide, during which the medusae were foraging with tentacles fully extended. Other associations between the medusae and fish were also observed at this time: presumed commensalism with juvenile Japanese horse mackerel, and predation by black scraper.

著者

Isao Sano Takumi Saito Jun-Ichi Miyazaki Akihisa Shirai Takeru Uechi Takaki Kondo Satoshi Chiba

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.15, no.2, pp.97-111, 2020-05-27 (Released:2020-05-30)

参考文献数

81

被引用文献数

7

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The evolutionary history and diversity of unionoid mussels in East Asia need to be clarified and would shed light on the formation process of the unique fauna of Japan. Unionoid mussels (Mollusca: Bivalvia) are unique models for understanding the process by which organisms have diversified before and after the formation of the Japanese archipelago. Unionoid mussels have poor dispersal ability, so it is thought that they would have been strongly influenced by the archipelago’s formation. Therefore, the speciation and diversification processes of mussels before and after the archipelago’s formation were investigated by analyzing the nuclear and mitochondrial DNA of a wide range of species, particularly those inhabiting East Asia. The evolutionary history and divergence time of these mussels were examined. Unionoid mussels were found to have higher endemicity than other freshwater organisms. Although most of the endemic unionoid mussels of Japan are likely to have diverged before the formation of the Japanese archipelago, some other Japanese unionoid mussel species, including species endemic to Lake Biwa, an ancient lake in Japan, potentially diverged after the Japanese archipelago began to separate from the continent. This suggest that adaptation to the unique habitat of the ancient lake has caused diversification in the mussels endemic to it.

著者

Mariko Kawamura Rina Ishihara Kohei Oshiro Masaki Ishida

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.18, no.1, pp.60-62, 2023-02-28 (Released:2023-03-02)

参考文献数

15

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We collected 43 medusae of Aurelia coerulea from Tanabe Bay, Wakayama, Japan, and measured the tubule lengths of 1,613 nematocysts at different growth stages: ephyra, juvenile, subadult, and adult. The median tubule lengths for ephyrae, juveniles, subadults, and adults were 72, 51, 79, and 58 µm, respectively. No nematocysts in ephyrae, juveniles, or subadults exceeded 200 µm in tubule length. In the tentacles of 15 adults, we detected nematocysts with tubule lengths exceeding 200 µm. The average proportion of nematocysts with long tubules was 9.1% in medusae with bell diameters of 110 mm or more, in contrast to only 1.0% in medusae with bell diameters of less than 110 mm. Among the 1,613 nematocysts examined, there were two different tubule groups with modes at 54 µm and 230 µm in length. Nematocysts in the short-tubule group were composed of microbasic euryteles and small isorhizas, whereas the long-tubule group was composed of only microbasic euryteles. These long tubules of microbasic euryteles can potentially penetrate not only large planktonic crustaceans but also human skin. The growth-related and intra-species variation in tubule length could also modify the degree of envenomation in humans.