Reproductive condition in two Malayan freshwater viviparid gastropods

Siamopaludina martensi and Filopaludina sumatrensis have typical viviparid reproductive systems with dimorphic spermatozoa and copulatory right tentacle in the male, and a large pallial brood-pouch in the female. Females outnumber males as in several other viviparids. Brood-pouches contained overall monthly averages of 0–14 developing young in S. martensi , 9–23 in F. sumatrensis , more than half of which were well-developed, later juveniles. Brood-pouch counts and ovary condition of both species varied in broad accordance with monthly rainfall, giving an irregularly seasonal pattern of annual change resembling those of several terrestrial Malayan snails. Juveniles emerge from the brood-pouch mostly at night. Alteration of aquarium conditions leads to temporarily accelerated release of young but does not permanently raise brood-pouch counts or rates of release.