Genus Prosthiostomum Quatrefages, 1845

Diagnosis (modified by Faubel 1984). Prosthiostomidae with marginal eyes along varying lengths of the anterior margin or encircling the entire margin; without marginal tentacles or pseudotentacles; a digestive system with frontally running main median intestine; male reproductive system with a pair of accessory vesicles, penis papilla armed with a pointed tubular stylet.

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