title: The ultrastructure of spermatozoa of the slender catfish Silurus microdorsalis (Teleostei, Siluriformes, Siluridae) with phylogenetic considerations.
abstract: The spermatozoa of the slender catfish Silurus microdorsalis examined using transmission and scanning electron microscopy are characterized by a tubular structure and the absence of axonemal fins. Their characteristics can be considered to represent a valid symplesiomorphy uniting the Siluridae and taxon-specific for this family. The tubules of Silurus spermatozoon are not observed in the other siluroids. Unusual tubules occur in Citharinus spermatozoa of Characiformes. In addition, there is a considerable similarity in the absence of axonemal fins between Siluridae and Characiformes. Thus the two shared characteristics provide strong evidence that there exists a phylogenetic link between Characiformes and Siluriformes. Silurus appears to be plesiomorphic in having lost the axonemal fins while retaining the tubules in midpiece. The spermatozoa of S. microdorsalis are similar to those of other siluroids having a spherical head with a deep nuclear fossa, a short midpiece and an elongated tail. However, there are some differences between Silurus and other siluroids in the orientation of the centrioles, the number of the mitochondria and the axonemal fins, and minor differences between S. microdorsalis and S. asotus, in particular the orientation of the centriolar complex, and the arrangement of the tubules and the mitochondria in the midpiece. The deep nuclear fossa represents a synapomorphy uniting the Siluriformes, while the shallow nuclear fossa and the absence of axonemal fins are shared by two orders, Characiformes and Cypriniformes.
authors.affiliation: Division of Science Education, Taegu University, Kyungsan, Korea.
authors.forename: Y H
authors.initials: YH
authors.lastname: Lee
authors.forename: K H
authors.initials: KH
authors.lastname: Kim
mesh_terms: D000818:Animals; D002397:Catfishes / Q000502:physiology*; D008297:Male; D015388:Organelles / Q000648:ultrastructure; D010802:Phylogeny; D013045:Species Specificity; D013094:Spermatozoa / Q000648:ultrastructure*