Halomonhystera parasitica n. sp. (Nematoda: Monhysteridae), a parasite of Talorchestia brito (Crustacea: Talitridae) in Portugal.

Halomonhystera parasitica n. sp. (Monhysterida: Monhysteridae) is described from the body-cavity and under the dorsal plates of the sandy beach amphipod Talorchestia brito Stebbing (Crustacea: Talitridae) in Portugal. The new species differs from previously described members of the genus by a combination of the following characters: four medium-sized cephalic setae; base of stoma with three blunt denticles; posterior dilated portion of stoma absent; amphids small, with width less than quarter of corresponding body width; amphids located less than two labial widths from anterior extremity; uterine eggs elliptical and unembryonated; gubernaculum lacks caudal process; and male tail with two separated pairs of postcloacal papillae and a single subterminal seta-like papilla. This is the first representative of the family Monhysteridae parasitic in the body-cavity of crustaceans. Approximately 48% of the amphipods examined contained various stages of H. parasitica.