Records of Palisadia Laseron, 1956 from south-western Japan and phylogenetic relationships of the genus within the family Eulimidae (Caenogastropoda: Vanikoroidea)

ABSTRACT Palisadia Laseron, 1956 is a little-known gastropod genus in the echinoderm-parasitic family Eulimidae (Caenogastropoda: Vanikoroidea). This genus has so far been reported from empty shells only, which are characterised by (1) small size, around 3 mm in length; (2) enlarged, strong varices on either side which protrude above the sutures; (3) a distorted subtriangular aperture; and (4) a columella with a shallow sinus. Recently, two live and two fresh empty shell specimens were collected in the Okinawa Islands, south-western Japan. The live specimens allowed us to observe their soft part morphology and investigate phylogenetic relationships using molecular approaches, which confirmed the familial assignment of the genus to Eulimidae. The present molecular phylogeny based on six gene sequences recovered Palisadia to form a monophylum together with the ophiuroid-parasitic genera Pyramidelloides, Eulima, Hemiliostraca, and Introphiuricola. Although the live specimens were collected as free-living form without host information, the present study suggests that species of Palisadia are temporary parasites of ophiuroids. In addition, Palisadia species may prefer cryptic habitats, because many specimens were collected from a submarine cave, the bottom sediment of reef crevices, and under corals.