Identification of the cercarial stage ofMaritrema arenaria(syn.M. gratiosum) (Trematoda: Microphallidae)

Abstract

Maritrema arenaria is a microphallid trematode found in the intestines of marine wading birds. The metacercarial stage occurs in barnacles, Semibalanus balanoides. To date the cercarial stage had not been identified. Large numbers of M. arenaria metacercariae were found in barnacles at one site on the north shore of Belfast Lough, N. Ireland (Irish Grid Reference D355,810) where a previously unidentified cercaria, Cercaria littorinae saxatilis V, was also abundant. Experiments were carried out to establish if C. littorinae saxatilis V developed into the metacercariae of M. arenaria. The experiments demonstrated that C. littorinae saxatilis V entered the cirri of feeding barnacles and later accumulated in the haemocoel close to the barnacle's gut. There the cercariae formed cysts which increased in size until they attained the structure of M. arenaria metacercariae. The study has clearly demonstrated that the cercariae of M. arenaria are those previously known as C. littorinae saxatilis V.