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Megadenus atrae n. sp., an endoparasitic eulimid gastropod (Mollusca) from the black sea cucumber Holothuria atra Jaeger (Aspidochirotida: Holothuriidae) in the Indo-West Pacific

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Abstract

An eulimid gastropod, Megadenus atrae n. sp., endoparasitic in the cloacal chamber of the black sea cucumber Holothuria atra Jaeger is described from Okinawa, Japan, as the fifth species of the genus. Conspecific specimens have also been found from southeast India, northeast Australia and New Caledonia. The generic assignment is justified by the presence of (i) a thick, long proboscis that bears a large fold (pseudopallium) near the base and a collar-like structure at the middle, (ii) a thin, globose shell that is covered by the pseudopallium, and (iii) sexual dimorphism with the female generally larger than the male. The new species is distinguishable from the four previously described congeners by its cauldron-shaped pseudopallium, moderately-developed collar of the proboscis and rounded basal lip of the shell. The comparisons of the size and sex of solitary and paired individuals support a previous hypothesis that the species of Megadenus Rosén, 1910 are protandrous with environmental sex determination. The present species occurs mostly as monogamous pairs despite its very low population density, implying that the presence of a conspecific individual acts as a cue for larval settlement. Both mechanisms would increase individual reproductive success in such permanent parasites with low prevalence and abundance as the species of Megadenus.

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Acknowledgements

We thank P. Bouchet, H. Fukumori, H. Hidaka and G. Kobayashi for their help in the fieldwork. Invaluable comments were provided by P. Bouchet and K. Seike for the improvement of the manuscript.

Funding

Financial support was provided by KAKENHI grant from the Japan Society for the Promotion of Science (nos 26291077 and 15J10840) and Sasakawa Scientific Research Grant from The Japan Science Society (25-529).

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Authors and Affiliations

  1. Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa, Chiba, 277-8564, Japan

    Tsuyoshi Takano & Yasunori Kano

  2. Swedish Museum of Natural History, Box 50007, 10405, Stockholm, Sweden

    Anders Warén

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  1. Tsuyoshi Takano
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  2. Anders Warén
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  3. Yasunori Kano
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Correspondence to Tsuyoshi Takano.

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All applicable institutional, national and international guidelines for the care and use of animals were followed.

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This article was registered in the Official Register of Zoological Nomenclature (ZooBank) as urn:lsid:zoobank.org:pub:73AECE62-07A8-4C09-99F5-B27B54370D5C. This article was published as an Online First article on the online publication date shown on this page. The article should be cited by using the doi number. This is the Version of Record.

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Takano, T., Warén, A. & Kano, Y. Megadenus atrae n. sp., an endoparasitic eulimid gastropod (Mollusca) from the black sea cucumber Holothuria atra Jaeger (Aspidochirotida: Holothuriidae) in the Indo-West Pacific. Syst Parasitol 94, 699–709 (2017). https://doi.org/10.1007/s11230-017-9731-7

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