ABSTRACT
Spermatozoa were used as phylogenetic characters for the Platyhelminthes in early studies such as those of Hendelberg (1969). The use of cladistic methods gave a new direction to these studies. Sperm characters were included in the definition of several major groups by Ehlers (1984, 1985a,b, 1986) and Brooks (Brooks 1989a; Brooks and McLennan 1993b). A critical assessment of sperm characters in the systems of Ehlers and Brooks was given later (Justine 1991a), and sperm characters were used for the construction of a phylogeny of the monogeneans, mainly the monopisthocotyleans (Justine 1991b, 1993). Sperm characters of the monogeneans have been incorporated, along with other morphological characters, into wider analyses of monogeneans (Boeger and Kritsky 1993, 1997, 2001, this volume). Sperm characters of the cestodes (Ba and Marchand 1995) were also given a cladistic interpretation (Justine 1998b), and were incorporated into a phylogenetic analysis of the group (Hoberg et al. 1997c). Although sperm characters have been used in a variety of phyla for phylogenetic reconstruction (Jamieson et al. 1995), the wide use of sperm characters in modern phylogenies is certainly a distinctive feature of the phylogenetics and taxonomy of Platyhelminthes, to an extent not seen in other invertebrate groups. Absence of fossils, lack of reliable, homologous morphological characters and extensive variation of sperm are probably responsible for this exception (Justine 1998c).
