A. Jespersen et J. Lutzen, Ultrastructure of the seminal receptacle and the dimorphic sperm in the commensal bivalve Mysella bidentata (Veneroida; Galeommatoidea; Montacutidae), ACT ZOOL, 82(2), 2001, pp. 107-115
The seminal receptacle and the euspermatozoa and paraspermatozoa of Mysella
bidentata were examined at an ultrastructural level and the results were c
ompared with earlier findings of the same and other species of the Montacut
idae. The euspermatozoon has a slender 13 mum long nucleus and a 1.1 mum lo
ng bullet-shaped acrosome. The acrosome of the paraspermatozoon is almost i
dentical in ultrastructure to that of the euspermatozoa but is longer (1.9
mum) and more slender and is bent at an angle to the diminutive nucleus (1.
1 mum long). The unpaired seminal receptacle is lined by a heavily ciliated
epithelium and a nonciliated epithelium with short and broad microvilli. E
uspermatozoa only are stored in the receptacle. They are densely packed and
orientated with their heads towards the non-ciliated epithelium. In this p
osition they develop numerous extremely fine microvilli from the acrosome w
hich apparently serve to attach them to the epithelial microvillar surface.
Stored sperm may presumably remain functional for at least six months. A p
ossible function of paraspermatozoa could be to clump sperm into sperm bags
to keep them in suspension.