Hydatina physis (Linnaeus, 1758)

Hydatina physis lives on intertidal and shallow subtidal lagoon reefs in the Marshalls. The best area is in some man-made reef quarries that range in depth from a few centimeters to about 3 meters. They are usually seen at night, when they emerge from their hiding places under the sand. The figured specimen in the two shots immediately below is a young one, measuring only 20mm in length. This specimen was observed on 20 November 1981 on sand at a depth of 8m on Enewetak Atoll's eastern lagoon reef.

The specimen figured below had a shell that measured 29mm. It was found at the base of a Halimeda plant in a Kwajalein lagoon algae patch at a depth of 8m on 27 July 2008. A fragment of a shell from the same area measured over 40mm; the full sized shell would have been well over 50mm, so these animals can get pretty large.

Created 27 January 2007
Updated 19 September 2008