In both sexes in F. latimarginata and F. cumingi the germ cell line in the gonad presents a centrifugal organization like in the vetigastropod Tegula tridentata (Potiez & Michaud, 1838) (Brown, 1992). The gametes of F. latimarginata and F cumingi travel
from the gonad to the right kidney through the renopericardial duct.
The similar organization of the reproductive system between the two
species does not show differences useful for making unequivocal
anatomical distinctions between them. The histological detail of the
genital duct (Figs. 3G, H) also fails to reveal interspecific
differences in relation to find an isolating reproductive mechanism of
morphophysiological type. Consequently, the reproductive system has
therefore little value as taxonomic tool at the species level.
Anatomical characteristics of the reproductive systems of these species
could be useful in making differentiations at higher taxonomic levels
or between less closely related species; however, differences in sperm
morphology have shown to be useful to distinguish between both species
(Collado & Brown, 2003).
Relations between the reproductive and
excretory systems of the Fissurellidae were controversial until now. In
the Ihering (1877) model, the gonad of Fissurella opens to the
right kidney from which there is no renopericardial connection. Boutan
(1885) was unable to find a renopericardial connection in Fissurella reticulata (da Costa) [= Diodora apertura (Montagu)], nor did Erlanger (1892) in five species of Fissurella. Boutan however described a "glande annexe" in the internal wall of the genital duct mF. reticulata females.
According to Boutan and Erlanger the gonad opened to the right kidney.
A renopericardial duct was recognized by Haller (1886, 1906) in a Fissurella species. In the Perrier (1896) model, the Fissurella gonad
opened to the right kidney, in which there was a renopericardial
connection. Ziegenhorn & Thiem determined that the reproductive
system in Fissurella crassa Lamarck, 1822 consisted of a gonad
that opened to the right kidney through a gonoduct which contained a
gland in its internal wall, and which was also observed in females of Fissurella oriens Sowerby, 1835 (under Fissurella alba Philippi, 1845) and Fissurella limbata Sowerby, 1835. For Ziegenhorn & Thiem the gland was the same as that of Boutan and was also found in Fissurella (= Diodora) nubécula (Linnaeus,
1758) males. Ziegenhorn & Thiem found a renopericardial duct in all
the species which they studied. In the Pelseneer (1898) model, the Fissurella gonad
opened to the renopericardial duct and the gametes were evacuated
through the right renal aperture. More recent studies, and reviews made
by Gabe (1951), Fretter & Graham (1962), Delhaye (1976) and
Haszprunar (1988) agreed with the Pelseneer observations. The Voltzow
(1994) model, based on the literature, shows two renopericardial
connections, one for each kidney, with the gonad opening to the right
The results of the present study show that in F. ¡atimarginata and F. cumingi the
gametes are transported to the distal region of the right kidney
through the renopericardial duct, which functions as a genital duct, as
well as draining the pericardium. In this manner, the renopericardial
duct represents a "nephrogonoduct" if we follow the terminology
correctly assumed by Pelseneer for this double functional duct. No
connection was observed between the gonad and the small left kidney in
both F. ¡atimarginata and F. cumingi, which also
discharges its contents to the mantle cavity. Andrews (1985), however,
described two renopericardial connections in Emarginula reticulata Sowerby,
1813, one for each kidney, the left one revealed ultrastructurally.
Fretter (1984) mentioned that the kidney, pericardial cavity, gonad,
and gonoduct were coelomic in origin, and that the connections between
them remained in some adult prosobranchs, just as in the case of the
two species considered in the present study.
The anatomy of the reproductive system in F ¡atimarginata and F. cumingi is similar to that described by Ziegenhorn & Thiem for Fissurella species.
A gland of unknown function associated with the genital duct like that
described by these authors is also found in F ¡atimarginata and F cumingi, both
in male and females. The gland present in other fissurelids seems to be
related with the pattern of development of the species; adding extra
material to the gametes for clustering the oocytes during spawning in
females (Boutan), or packaging the sperms in spermatophores in males
(Medem, 1945). In the present study, we were unable to know if the
gland adds extra material to the gametes. Another interesting
possibility that could not be discarded is that secretions from the
gland had a communication role, releasing a chemical like a sex
pheromone to mediate an appropriate gregarious response and gamete
evacuation from conspecifics. The simultaneous hermaphrodite nudibranch
mollusk Aplysia with internal crossed fertilization, produces
water-borne attractin pheromones in the oviduct and are released during
egg laying (Cummins et al., 2005). Attractins are a family of
small proteins in invertebrates that stimulates the formation and
maintenance of mating and egg-laying aggregations (Cummins et al.). It is possible that the gland, as a specialization of the gonoduct in Fissurella, could
produce substances like attractins acting as chemical signals in sex
communication to induce aggregation and release of gametes improving
external fertilization. Although no gland has been associated with the
gregarious behavior, sexual aggregation associated with gamete release
has been described in vetigastropod species (Fretter & Graham,
Fissurella is one of the youngest genera within the Family Fissurellidae (McLean, 1984). Local species of Fissurella in
the Chilean coast appeared in the Pliocene, and increased diversity in
the Pleistocene (Herm, 1969). Although these species may have evolved
structures adapted for radiating to new habitats in this relatively
short geological period, this would not be the case for the
reproductive system, which probably requires a longer time period for
greater specialization and differentiation.
We thank Drs. Bernardita Campos and Doris Oliva for their valuable comments related to preparation of this MS.