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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