Abstract
Knowledge of the testis structure is important for gastropod taxonomy and phylogeny, particularly for the comparative analysis of sympatric Littorina 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. The testis of adult males consists of numerous lobules filled with multicellular cysts containing germline cells at different stages of differentiation. Each cyst is formed by one cyst cell of somatic origin. Here, we provide evidence for the existence of two ways of cyst formation in Littorina saxatilis. One of them begins with a goniablast cyst formation; it somewhat resembles cyst formation in Drosophila testes. The second way begins with capture of a free spermatogonium by the polyploid cyst cell which is capable to move along the gonad tissues. This way of cyst formation has not been described previously. Our data expand the understanding of the diversity of spermatogenesis types in invertebrates.
Highlights
Gastropod mollusks are key species in many marine, freshwater and land communities. They serve as the first intermediate hosts for trematodes and in this way, they support natural foci of epizootic diseases including important for man and domestic animals [1,2]
We have recently found that spermatogenesis of the rough periwinkle Littorina saxatilis, a marine gastropod, has some surprising similarities with spermatogenesis of Drosophila rather than most mollusks [33]
We provide evidence for the existence of specialized somatic cells in the L. saxatilis testis wall, referred here as Sertoli-like cells (SLCs)
Summary
Gastropod mollusks are key species in many marine, freshwater and land communities. They serve as the first intermediate hosts for trematodes and in this way, they support natural foci of epizootic diseases including important for man and domestic animals [1,2]. The cystic mode of spermatogenesis implies that germline cells develop within a cyst (spermatocyst)— the basic functional unit of the gonad.
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