Karyotypes and chromosome morphologies of <i>Megalodiscus temperatus</i> and <i>Philophthalmus gralli</i>

Abstract

Abstract The karyotypes of two hermaphroditic trematodes, Megalodiscus temperatus and Philophthalmus gralli , were described and compared as to chromosomal morphology and constitutive heterochromatin constitution. The haploid number of chromosomes for both species is 10 and both karyotypes are composed mainly of acrocentric chromosomes. Constant heteromorphism of the No. 10 chromosomes was found in M. temperatus . The heteromorphic chromosomes differ is size and heterochromatin constitution. The possible mechanisms of chromosomal dimorphism in M. temperatus and its significance in the evolution of sexchromosome differentiation in trematodes are discussed.