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This study describes the microscopic anatomy of the reproductive systems of the …

Biology Articles » Anatomy & Physiology » Anatomy, Animal » Microscopic Anatomy of the Reproductive System in Two Sympatric Species of Fissurella Bruguiére, 1789 (Mollusca: Vetigastropoda) » Introduction

- Microscopic Anatomy of the Reproductive System in Two Sympatric Species of Fissurella Bruguiére, 1789 (Mollusca: Vetigastropoda)

An unusually large number of relatively large species of Fissurella occupy the temperate South American coastline (McLean, 1984). Taxonomic separation of these species has been historically based on the Typological Species Concept, relying mainly on externally visible shell characteristics. Sympatry of some of these species, coupled with individual variability within natural populations (Ramirez, 1974; McLean) has in the past produced some taxonomic confusion with regard to species identification among these limpets. It was resolved to some extent by McLean's synonymy which recognized 13 species from a previous total of 58 names based on characters of the shells, epipodium, and in some cases radulae, complemented by data on their geographic distributions.

The vetigastropods, which include Fissurella latimarginata Sowerby, 1835 and F. cumingi Reeve, 1849, release their gametes into the surrounding seawater at spawning. It is typical within this group that the gametes are transferred from the gonad to the distal portion of the right kidney through a genital duct, and are released to the exterior through a right kidney opening which opens to the mantle cavity. The detailed anatomy of the reproductive system in the Fissurellidae, however, is subject to some controversy. Unresolved discussions have been centered on the location of the opening of the genital duct, on the presence of a gland associated with the genital duct, and on the existence of a renopericardial canal (Boutan, 1885; Erlanger, 1892; Ziegenhorn & Thiem, 1925; and more references below). Until the present, no data have been presented on the microscopic anatomy of the reproductive systems in F. latimarginata and F. cumingi, and consequently has not been available for anatomical analysis of the reproductive system neither to be used in taxonomic differentiation, particularly with regard to structures which may help explain their interspecific reproductive isolation. Among the different barriers of separation between species, a morphophisiologycal isolating mechanism has been proposed in relation to reproductive systems that would prevent the fertilization due to anatomical incompatibilities (Dobzhansky et al, 1980; Savage, 1971), but has been controversial in gastropods because anatomical differences between closely related species are lacking (Graham, 1965; Houston & Hatfield, 1981).

The objective of the present study was to make a comparative microscopic description of the morphology of the reproductive systems ofF. ¡atimarginata andii cumingi to test the existence of a possible isolating reproductive mechanism of morphophysiological type, and consequently to determine if the findings provide a valid taxonomic characteristic to distinguish these sympatric species.

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