Molluscan ResearchISSN 1323-5818
 An international journal of the Malacological Society of Australasia and 
the Society for the Study of Molluscan Diversity published by Magnolia Press

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Molluscan Research 31(2): 114-124; published 28 Jul. 2011
Copyright © The Malacological Society of Australasia & the Society for the Study of Molluscan Diversity

Morphology of an endosymbiotic bivalve, Entovalva nhatrangensis (Bristow, Berland, Schander & Vo, 2010) (Galeommatoidea)


1Biological Institute, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen Ř, Denmark

2Department of Biology, University of Bergen, N-5020 Bergen, Norway

*Corresponding author, Email:



We describe the morphology of Entovalva nhatrangensis Bristow, Berland, Schander & Vo, 2010, an endosymbiontic bivalve living in the oesophagus of Holothuria spinifera and H. leucospilota in Vietnam. The delicate shells are entirely internalized. The body is very small compared to the foot, which is dorso-ventrally flattened and contains the digestive diverticula and the fertile parts of the gonads. Even though the gills are small, they probably serve in collecting suspended matter, and in addition, the species clearly feeds on benthic diatoms, which it probably sorts out from the contents of the host’s gut. The species is a protandric hermaphrodite. Most males have a total length of 1.5–3.0 mm and above that size start changing sex to become females, which may attain a total length of nearly nine mm. Sperm is transferred in spermatophores with a solid wall produced by glands within the male siphon. One to three spermatophores are placed on the gills of females and the ova become fertilized as they pass from the genital pores to the siphon, where they are brooded until released as D-larvae.

Key words: functional anatomy, hermaphroditism, protandry, spermatophore, Holothuria spinifera, Holothuria leucospilota, Bivalvia, Heterodonta

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