Postembryonic development of certain tetraphyllidean and trypanorhynchan cestodes with a possible alternative life cycle for the order Trypanorhyncha

Abstract

Development of metacestode stages obtained from experimental infection of copepods (Tigriopus californiens) with one species of tetraphyllidean (Acanthobothrium olseni) and two species of trypanorhynchs (Lacistorhynchus tenuis and Parachristianella monomegacantha) is described. Both A. olseni and L. tenuis produced procercoids lacking a cercomer. The procercoid of A. olseni had paired dorsal and ventral osmoregulatory canals which connected to the exterior both laterally and at the posterior end, while those of L. tenuis emptied only posteriorly. A procercoid was not produced by P. monomegacantha; instead development continued to an immature plerocercus stage with developing proboscides and bothridia.The contrasting metacestode stages of the trypanorhynchs L. tenuis and P. monomegacantha indicates the possibility of two different life cycles in this group. One, in which a procercoid develops, requires a teleost intermediate host as well as a crustacean intermediate host. The second life cycle would require only a microphagous crustacean intermediate host in which a plerocercus stage infective to elasmobranchs may develop.