New data on spermatogenic cyst formation and cellular composition of the testis in a marine gastropod, .

Knowledge of the testis structure is important for gastropod taxonomy and phylogeny, particularly for the comparative analysis of sympatric species. Observing fresh tissue and squashing fixed tissue with gradually increasing pressure, we have recently described a peculiar type of cystic spermatogenesis, rare in mollusks. It has not been documented in most mollusks until now.

Spermatogenesis and lobular cyst type of testes organization in marine gastropod Littorina saxatilis (Olivi 1792).

Although individual stages of spermatogenesis in Littorina saxatilis are well studied at the electron microscopic level, the gonad structure and the spatial localization of gametes at different stages of maturation remain unclear. Using differential-interference contrast (DIC) for observations of fresh tissue we show that the mature testis consists of numerous ovoid lobules forming larger lobes. The lobules of intact mature testes of L.

LOSP: A putative marker of parasperm lineage in male reproductive system of the prosobranch mollusk Littorina obtusata.

Reproductive isolation is the key attribute of biological species and establishment of the reproductive barriers is an essential event for speciation. Among the mechanisms of reproductive isolation, gamete incompatibility due to the variability of gamete interaction proteins may drive fast divergence even in sympatry. However, the number of available models to study this phenomenon is limited.

A potential species-specific molecular marker suggests interspecific hybridization between sibling species Littorina arcana and L. saxatilis (Mollusca, Caenogastropoda) in natural populations.

Three sister species of rough periwinkles, viz. Littorina saxatilis (Olivi 1792), L. arcana (Hannaford Ellis 1978) and L.