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

• Published in: Systematic parasitology Vol. 94; no. 6; pp. 699 - 709
• Main Authors: Takano, Tsuyoshi, Warén, Anders, Kano, Yasunori
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01-07-2017; Springer Nature B.V
• Subjects: Abundance; Agriculture; Animal Anatomy; Animal Ecology; Animal Systematics/Taxonomy/Biogeography; Animals; Aspidochirotida; Biomedical and Life Sciences; Breeding success; Congeners; Diversity of life; Endoparasites; Female; Gastropoda - anatomy & histology; Gastropoda - classification; Histology; Holothuria atra; Holothuriidae; Japan; Life Sciences; Livets mångfald; Male; Megadenus; Megadenus atrae; Mollusca; Monogamy; Morphology; New species; Pacific Ocean; Parasites; Physical characteristics; Population density; Proboscis; Reproduction; Sea Cucumbers - parasitology; Sex determination; Sexual dimorphism; Shells; Species Specificity; Zoology
• ISSN: 0165-5752; 1573-5192; 1573-5192
• DOI: 10.1007/s11230-017-9731-7

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
.