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The family Prosthiostomidae Lang, 1884, is placed in the superfamily Euryleptoidea Faubel, 1984.
Prosthiostomidae species have a long, slender or elongated oval form of the body, with a rounded anterior end and a tapering posterior end. They are without any trace of tentacles, and have the male and female gonopores separate.
There are according to WoRMS 5 genera in the family Prosthiostomidae Lang, 1884.