Ultrastructure of euspermatozoa and paraspermatozoa in the volutid gastropod Adelomelon ancilla (Lightfoot, 1786) (Caenogastropoda, Volutidae)

ZABALA, SOLEDAD; HERMIDA, GLADYS; GIMENEZ, JULIANA

HELGOLAND MARINE RESEARCH

SPRINGER

Año: 2009 vol. 63 p. 181 - 188

1438-387X

The ultrastructure of the euspermatozoa and the paraspermatozoa is investigated in Adelomelon ancilla, through histological section observed by transmission electron microscopy (TEM). Euspermatozoa of A. ancilla consist of: (1) a conical acrosomal vesicle (with a short basal invagination, constricted anteriorly) which is flattened at the apex and associated with an axial rod, a centrally perforated basal plate and a short accessory membrane; (2)  a rod-shaped, solid and highly electron-dense nucleus (with a short basal fossa containing a centriolar complex and a initial portion of a 9+2 axoneme); (3) an elongate midpiece consisting of the axoneme sheathed by 5-6 helical mitochondrial elements each exhibiting a dense U-shaped outer layer; (4) an elongate glycogen piece ( where the axoneme is sheathed by nine tracts of glycogen granules); (5) a dense annulus at the junction of the midpiece and glycogen piece and (6) a short free tail region ( where the axoneme is surrounded only by plasma membrane). We observed a parasperm in A. ancilla. This is vermiform in shape and is composed of multiple axonemes and extensive cytoplasm with  numerous vesicles, and mitochondria are scattered inside the axonemes. Sperm of A. ancilla is characterized by the euspermatozoa type 2 and the paraspermatozoa morphology belongs to Type 5. The U shaped electrodense mitochondrial element in the midpiece of the eusperm and the constriction in the acrosomal vesicle present in A. ancilla are exclusive. We suggest that these characteristics could have toxonomic importance, because these was observed in other volutids and have not been observed in the rest of caenogastropods studies. We consider that the morphology of paraspermatozoa in A. ancilla corresponds to the “lancet” type.