The smile of Amphiporus nelsoni Sanchez, 1973 (Nemertea: Hoplonemertea: Monostilifera: Amphiporidae) leads to a redescription and a change in family

—A common intertidal hoplonemertean species, Amphiporus nelsoni Sanchez, 1973, from Chile is re-described based on the investigation of material from the type locality and one other locality in Chile. The species is transferred to the genus Prosorhochmus Keferstein, 1862 (Prosorhochmidae) based on the presence of a dorsal epidermal fold, i.e., "prosorhochmid smile" on the bilobed head, truncated stylet basis, well-developed frontal organ with characteristic epithelial specialization, structure of the nephridial system and other characters of internal anatomy. Placement of this species into Prosorhochmus expands the geographical distribution of the genus, previously known only from the North Atlantic and Mediterranean, to the South Pacific. Interestingly, Prosorhochmus nelsoni (Sanchez, 1973) is characterized by separate sexes and oviparity, unlike all the other members of the genus, which combine hermaphroditism with ovoviviparity. We compare P. nelsoni to the other species of Prosorhochmus and reassess some of the morphological characters used in the systematics of the genus. The genus Prosorhochmus currently of photomicrographs and diagrams. We comprises four marine intertidal species demonstrate that morphological charactercombining two relatively uncommon charistics clearly place A. nelsoni in Prosoacteristics among nemerteans, hermaphrorhochmus, and we compare it to the other ditism and viviparity. A total of nine spevalid species of the genus Prosorhochmus. cies have been described in the genus, but two of these have been synonymized with Materials and Methods Prosorhochmus claparedii Keferstein, 1862 and three others are considered species inThree attempts over a 15-year period quirendae. The four valid species are found failed to locate the type material, consisting in the North Atlantic or Mediterranean of a series of histological sections of a ho(Gibson & Moore 1985). The original delotype and three unsectioned paratypes in scription of Amphiporus nelsoni Sanchez, 9% sea water formalin originally deposited 1973 was mainly based on external appearwith the Museo de Historia Natural, Santiance. In this paper we re-describe A. nelsoni ago, Chile. The current redescription is on the basis of histological sections of mabased on investigation of the series of histerial from the type locality and recently tological sections of three specimens collected material from another locality, (USNM 173162—173164) collected and and we illustrate the description with a set identified by Malva Sanchez (who original484 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON