A Cercaria of the Trematode Family Haploporidae

Abstract

Cercaria caribbea LII is described and evidence presented that it is the larva of a haploporid, probably Hapladena varia. The cercaria develops in simple rediae in Zebina browniana and encysts in the open. It is biocellate, the tail is slender and unadorned, and the excretory system is stenostomate with a nonepithelial bladder and primary pores at the sides of the tail in the embryo. Affinity of the Haploporidae to the Haplosplanchnidae is indicated and the Megasolenidae and Waretrematidae are considered synonyms of Haploporidae. Of the digenetic trematode families represented by parasites of marine fishes in the Gulf-Caribbean region, the Haploporidae is one of the few for which no life history has been demonstrated or at least convincingly suggested by morphological similarities of cercariae and adults. La Rue (1957) did not include that family in his scheme based on the embryology of the excretory system and on larval as well as adult stages. Because those features are essential to the interpretation of affinities between families and more inclusive taxa, information concerning the life cycle in the Haploporidae was a particular objective of studies in the Caribbean region during the first 7 months of 1961. This paper reports more fully results published in an abstract (Cable, 1961). At the laboratory in Curacao, Mr. Gerrit Klay called my attention to minute white snails crawling at night up the glass of an exhibit aquarium to which he had added fresh sand from shallow water nearby. In daytime, most of them remained hidden in the sand. Several snails were crushed and nearly all of them were infected with a minute hemiurid cercaria, but one contained a large, biocellate gymnocephalous species. On subsequent nights, further lots of snails were collected and isolated. Before morning about 5 per cent shed the large Received for publication 20 November 1961. *This study was supported by National Science Foundation Grant G-14691. The author is indebted to Dr. H. E. Coomans, American Museum of Natural History, for identification of the molluscan host, and to the Director, Dr. Ingvar Kristensen, and staff of the Caraibisch MarienBiologisch Instituut for laboratory facilities and assistance. species, one or two cercariae per snail. The larvae rarely failed to encyst before 8:00 AM when their detached tails were still moving about actively. The cercaria has a combination of features not found in any other marine larval trematode reported from the Gulf-Caribbean region. Its morphology and ecology indicate that the adult is a species of Hapladena, probably H. varia, which is a common parasite of surgeonfishes in that region. In both the cercaria and adult, the cuticle is spinose anteriorly, the body contains yellow pigment and eyespots or remnants thereof, the digestive system is the same, and there is complete agreement in essential features of the excretory system (cf. figs. 1 and 6). Encystment of the cercaria in the open and the absence of penetration glands indicate that the life history does not include a second intermediate host but, instead, is completed when the definitive host ingests the free metacercaria, probably with vegetation. Although time limitation and other factors precluded controlled feeding experiments, several young Acanthurus hepatus were placed in an aquarium with infected snails and examined at intervals thereafter. Some of the fish yielded very young worms that were smaller than any found in a large number of similar A. hepatus examined without previous exposure to infection in the laboratory. In an extensive collection of fishes from the area where infected snails were obtained, no haploporid was found except the Hapladena species in surgeonfish. But because the adult has not been demonstrated beyond doubt, the cercaria is described and designated as an additional species in the series reported from Puerto Rico (Cable, 1956).