The Estuarine Mud Snail, Nassarius Obsoletus: Abnormalities in the Reproductive System

Females of the dioecious snail Nassarius obsoletus may have three male characteristics: a penis, a vas deferens, and the convolution of a normally straight gonadial oviduct to resemble a stunted mimic of the vesicula seminalis in the male. The first characteristic is the most common and the last is the least common. Collectively these characteristics were called imposex. A system for evaluating its frequency of occurrence and intensity of expression was developed. The frequency and intensity of imposex was similar among different age groupings of snails, though there may be a trend towards less imposex in juveniles. The differences in the frequency and intensity of imposex between groups of parasitized and unparasitized females were very small. In males the reduction of penis size due to parasites was much larger. This pattern ofimposition of male characteristics on females is a new syndrome which does not resemble reported forms of hermaphroditism or pseudohermaphroditism related to age or parasitism.