Nassarius dorsatus

Nassarius dorsatus, called the channeled nassa, is a marine gastropod mollusk belonging to the family Nassariidae—the group that includes Nassa mud snails and dog whelks. Its shell, which is ovate and conical, ranges from 15 mm to 45 mm in length. The surface is smooth and uniformly ashy white. The spire consists of eight whorls; the upper ones are slightly plaited, while the lowest whorl is fairly large and marked with nearly straight, longitudinal lines that are close together and tinged a slightly deeper reddish color.

Six or seven furrows decorate the base of the shell. The ovate aperture is white inside, with a fawn-colored interior. The thick outer lip curves toward the base and rises externally into a thick, very prominent margin; it is striated along its entire inner length.

The left lip is thick and partly covers the columella, which is adorned with guttules along half its length—the uppermost guttule being much more pronounced than the others. At the columella’s base there is a very prominent fold that ends in a guttule shaped like a flattened point. This marine species occurs in the tropical Western Pacific, off East India, the Philippines, Papua New Guinea, and Australia (New South Wales, the Northern Territory, Queensland, and Western Australia). Two parasites recorded from Australia are Stephanostomum-like cercariae: Cercaria capricornia VII and Cercaria capricornia VIII.