SPERMATOZOA AS PHYLOGENETIC CHARACTERS FOR THE EUCESTODA

Spermatozoon ultrastructure and spermiogenesis are significant charact ers for phylogenetic inference. Sperm ultrastructure is reviewed from the: literature in 56 species of Eucestoda. Data are available for 11 of the 12 orders of Eucestoda (Lecanicephalidea excepted), but in some orders data are scarce and often limited to a single species. Spermio genesis and sperm ultrastructure in the Eucestoda is compared to that of other parasitic Platyhelminthes, with emphasis on structures of phy logenetic interest. Nor only the descriptions of sperm structure, but those of the process of spermiogenesis. are necessary to define charac ters. Synapomorphies based on sperm ultrastructure for the Eucestoda i nclude the absence of a mitochondrion in mature sperm and the presence of a crested body. A proposed synapomorphy for the Cyclophyllidea + T etrabothriidea is the twisting of the peripheral microtubules; the abs ence of intercentriolar body and the absence of striated roots in the spermatid may constitute additional synapomorphies for this assemblage . Absence of flagellar rotation during spermiogenesis is synapomorphic for the Cyclophyllidea, and absence of proximodistal fusion could be synapomorphic for a parr of the Cyclophyllidea. Several other characte rs could be useful for understanding phylogeny within the Eucestoda. T he polarity of these characters could in several cases be determined, but diagnoses for taxa or relationships based on synapomorphies cannot be specified unequivocally due to putative convergence. Such characte rs and their putative polarity include: (1) the number of axonemes in mature spermatozoon (plesiomorphic = 2: apomorphic = 1); (2) size and number of crested bodies (p = 1; a = several); and (3) angle of twiste d microtubules: shape of nucleus (p = compact cord; a = crescent and a nnulus). Additional apomorphic attributes include (1) presence of a pe riaxonemal sheath (a putative synapomorphy for the Cyclophyllidea + Te trabothriidea if reversals are postulated in certain cyclophyllideans) : (2) presence of proteinaceous transverse walls: (3) presence of dens e granules: and (4) shape of apical cones and posterior structures. St udies of sperm structure in the poorly known orders and additional com parative studies in the Cyclophyllidea are expected to provide new inf ormation for elucidation of phylogenetic relationships.