Short communication. First record of Torticaecum sp. (Trematoda: Didymozoidae) in the chaetognath Serratosagitta serratodentata (Krohn, 1853) from Caribbean waters

Abstract

From samples collected in the Caribbean Sea during February, March, May and August 1991, a total of 22 508 holoplanktonic chaetognaths were caught. During the analyses of the samples, one non-cysted specimen of didymozoid metacercaria was found in the coelom of the chaetognath Serratosagitta serratodentata (prevalence 0.004%). Owing to the lack of an authentic stomach and the morphology of the intestine, this trematode seems to belong to the Torticaecum larval type. This is the first report of both the chaetognath species as a host and the geographical locality for this parasite. Trematode larvae from the family Didymozoidae have been previously recorded in animals from the planktonic realm (Dollfus, 1963; Madhavi, 1968; Nagasawa and Marumo, 1979; Theodorides, 1989). Cable and Nahhas (1962), based on the presence of one single larva recorded in adult cirripedians, assumed that these crustaceans were intermediate hosts. Yamaguti (1970) mentioned small fish as possible paratenic hosts, as large marine pelagic fish, and more rarely freshwater fish species, are the final hosts most of the time (Yamaguti, 1971). Reports of these types of trematodes as parasites in zooplankton communities are extremely scarce around the world. Regarding chaetognaths as hosts, Dollfus (1960) registered a larval form (Metacercaria sagittae) in Sagitta enflata in Castiglione (Algeria), Reimer et al. (1971) reported a didymozoid metacercaria in Sagitta elegans in the North Sea and Oresland (1986) found them in Sagitta setosa from samples collected off Plymouth (UK). In all cases, the authors did not specify whether the parasites found belonged to the Monilicaecum or Torticae- cum larval type. On the other hand, Reimer et al. (1975) reported eight chaeto- gnath species from the Atlantic Ocean as being parasitized with metacercaria of the family Didymozoidae, apparently of the Monilicaecum type (Shimazu, 1978). The purpose of this work is to describe the metacercaria of Torticaecum found in the coelom of Serratosagitta serratodentata (Krohn, 1853) and to report the Caribbean Sea as a new geographical area for this parasite.