The Half-smooth Odostome, Boonea seminuda (C.B. Adams, 1839) is a member of the marine gastropod family Pyramidellidae, a group of small species that in many cases are ectoparasites (parasites on the outer part of the body) on other mollusks. Its conical, tapered shell measures about 5 mm (about 0.2 inch). It has a sculpture of 4–6 spiral cords with squarish nodules. Its color is translucent-white. Half-smooth Odostomes are known to parasitize Common Atlantic Slipper Snails, Crepidula fornicata, and Bay Scallops, Argopecten irradians.
The Half-smooth Odostome, Boonea seminuda, from Sanibel. Photo by José H. Leal.