Nutritive Egg Formation in the Marine Snails Crepidula dilatata and Nucella crassilabrum

Summary

Both frequency and morphology of the nutritive eggs in the snails Crepidula dilatata and Nucella crassilabrum were analyzed. In both species, nutritive eggs constitute over 90% of the eggs deposited in each capsule. Marked differences in nutritive eggs exist between these species with respect to morphological and cytological characteristics.

Nutritive eggs of C. dilatata remain uncleaved and in their cytological characteristics resemble oocytes whose development becomes arrested at the stage of germinal vesicle. Although the eggs of this snail are dimorphic in size, such dimorphism is not correlated with the fate of these cells. Nutritive eggs of N. crassilabrum typically abort their development at the stage of zygote cleavage divisions and anarchic cleavage occurs only in a small fraction of them (X = 5–6%).

The nature of these food eggs is discussed. Our findings suggest that, at least in C. dilatata, the mechanisms of nutritive egg formation reside in properties of the oocyte.