Sperm ultrastructure in Kellia suborbicularis (Bivalvia: Galeommatoidea: Kellidae).

The sperm cells of Kellia suborbicularis are narrow with a short bullet-shaped acrosome, a 5.0–5.5 µm long and 0.4–0.6 µm broad nucleus, and a short midpiece with a ring of five mitochondria. The disposition of the subacrosomal substance into a coronet-like formation is unique, and the sperm structure offers no clue to the relationship between Kellia and other galeommatoidean genera. The possible significance of narrow elongate sperm for their entry into the brood pouch is discussed. [ABSTRACT FROM AUTHOR]