Purpuradusta fimbriata, Marshall Islands

Purpuradusta fimbriata (Gmelin, 1791)
Fringed cowry, 7.6-15.75mm

Purpuradusta fimbriata is one of the smaller cowries and lives in a wide range of atoll habitats. In can be found under rocks at depths of about 3m or more during the day on shallow lagoon subtidal reefs, or wandering about in seaward surge channel ledges and caves at night. It can also be found on shipwrecks and lagoon pinnacles as deep as 40m at least. Purpuradusta fimbriata is very similar to and often difficult to distinguish from Purpuradusta microdon and P. minoridens. Until one is familiar with the differences, it is usually necessary to compare specimens to determine which is which. Purpuradusta fimbriata has the largest teeth of the three, becoming noticeably larger on the anterior columellar side. All three species have three light transverse bands across the shell beneath the speckling of brown flecks; in P. fimbriata, the central band is more prominent than the other two, and it usually forms a darker but very irregular middorsal blotch that is usually not present in the other two species, both of which tend to have more regularly spaced dorsal spotting. Purpuradusta fimbriata is distributed widely across the Indo-Pacific and has been split into several subspecies, with the one in the Marshall Islands being Purpuradusta fimbriata marmorata.