Planaxidae is a small family of gastropods with about 22 species worldwide. These animals are mostly marine and are usually found on rocky shores in the tropics and subtropics (Healy and Wells 1998). Their intertidal habitats, where they cluster under rocks, are similar to those of the littorinids, although planaxids appear to be photonegative. Shells appear to be similar to those of littorinids; anatomical features such as open pallial ducts, aphallic males, cerithioid euspermatozoa, and multiflagel-late paraspermatozoa place them as cerithioideans (Healy and Wells 1998). In Planaxidae the shell is variable and relatively small (5 to 25 mm, or Vs to 1 in) and is either tall and conic without a true umbilicus (Planaxinae) or umbilicate, short, and turbinate (Fossarinae). The aperture is wide and oval to round. In Planaxinae the outer lip of the aperture is thick and shows a siphonal notch. In Fossarinae the outer apertural lip may be thin to somewhat thick and shows little if any evidence of a siphonal opening. The corneous, paucispiral operculum shows a terminal or sub terminal nucleus. The adult male shows sexual dwarfism, which may suggest the probability of protandrous hermaphroditism (Houbrick 1987b; Healy and Wells 1998). On the Texas coast Planaxidae is represented by 2 genera and 2 species whose size ranges from 2 to 6 mm