Systematic Parasitology

, Volume 94, Issue 6, pp 699–709 | Cite as

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

Article

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.

Notes

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).

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

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

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Copyright information

© Springer Science+Business Media Dordrecht 2017

Authors and Affiliations

  1. 1.Atmosphere and Ocean Research InstituteThe University of TokyoKashiwaJapan
  2. 2.Swedish Museum of Natural HistoryStockholmSweden

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