Ultrastructure of euspermatozoa and paraspermatozoa in the volutid snail Adelomelon ancilla (Mollusca: Caenogastropoda)

Abstract

The ultrastructure of the euspermatozoa and the paraspermatozoa is investigated in Adelomelon ancilla, through histological section observed by transmission electron microscopy. Euspermatozoa of A. ancilla consists of: (1) a conical acrosomal vesicle (with a short basal invagination, constricted anteriorly) which is Xattened at the apex and associated with an axial rod, a centrally perforated basal plate and a short accessory membrane, (2) a rodshaped, 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 taxonomic 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.

Ultrastructure of euspermatozoa and paraspermatozoa in the marine gastropod Adelomelon beckii (Caenogastropoda, Volutidae)

“…This also was found in Zidona dufresnei and Adelomelon ancilla (Giménez et al 2008;Zabala et al 2009), both belonging to the subfamily Zidoninae.…”

“…In A. beckii, in particular, the outer layer of each mitochondrial element is very electron dense, with a U-shape proWle in transverse section, coinciding with the other volutids studied (Giménez et al 2008;Zabala et al 2009). …”

“…The structure of the nucleus, with a basal invagination where the axoneme is inserted, is similar to that in most mesogastropods (Healy 1982(Healy , 1986a(Healy , b, 1994(Healy , 1996b and some neogastropods (Giménez et al 2008;Zabala et al 2009). …”

“…In other species of the superfamily Muricoidea (West 1978;Jaramillo et al 1986;Gallardo and Garrido 1989; Giménez et al 2008;Zabala et al 2009), the mid-piece is formed by mitochondrial elements helically arranged around the axoneme. In A. beckii, in particular, the outer layer of each mitochondrial element is very electron dense, with a U-shape proWle in transverse section, coinciding with the other volutids studied (Giménez et al 2008;Zabala et al 2009).…”

“…This species as well as some others of the family, is commercially exploited and recently detailed studies have been undertaken on its reproductive biology (Arrighetti 2009). The ultrastructure of eu-and paraspermatozoa of some species of the family Volutidae has also been described (Giménez et al 2008;Zabala et al 2009). However, a detailed description of both types of sperm has not been reported at ultrastructural level for Adelomelon beckii, except for some preliminary results on euspermatozoa ).…”