Ultrastructure of the spermatozoon of Lepidogalaxias salamandroides and its phylogenetic significance.

The spermatozoon of Lepidogalaxias salamandroides possesses an acrosome (putative), one or two perforatoria (putative) but no nine-triplet centrioles. Two elongated mitochondria (12 micron long) are situated in parallel between the nucleus (20 micron long) and the axoneme (53 micron long). The above features are unique among other teleosts with internal fertilization. The presence of an "acrosome" in this primitive teleost supports the hypothesis that this structure has been secondarily lost in teleosts during evolution. The uncertainty of phylogenetic placement of this fish is reflected by its unique sperm ultrastructure.