Spermatozoon ultrastructure in seven South American species of Tegula Lesson, 1835 (Mollusca: Vetigastropoda) and the phylogenetic implications for the subfamily Tegulinae

Abstract

This study presents results of the examination of the ultrastructure of the spermatozoon of seven South American species of Tegula using light and transmission electron microscopy. In all cases the spermatozoa were of the primitive or ect-aquaspermatozoon type, common in species which employ external fertilization as part of their reproductive strategy. The spermatozoon of Tegula, from anterior to posterior, are composed of: (a) a bullet-shaped head with an anterior acrosome and a basal nucleus, (b) a mid-piece with a prevalent number of five mitochondria plus proximal and distal centrioles, and (c) a flagellum with a 9+2 arrangement of microtubules. The ultrastructural dimensions of the spermatozoa and the characteristics of the acrosome and the nucleus of the Tegula species studied here, as well as those previously published in the literature, showed that each species produces male gametes having a species-specific morphology. The results also suggest that the ultrastructure of the spermatozoon could be potentially useful for recognizing subgenera within Tegula. The comparative study showed that some characters of the spermatozoon of the Tegulinae (e.g. length of the head, acrosome shape, acrosome length as percentage of total head length) agree with fossil, morphological and molecular evidence which suggest that members of this subfamily are more closely related to representative of the family Turbinidae.