F. latimarginata and F. cumingi are
gonochoric species. The reproductive system in both these species is
simple, and copulatory organs are absent. The reproductive system is
intimately associated to the excretory systems. The right kidney is
much more developed than the left kidney in both species and there is a
single gonad which is connected only with the right kidney. Upon
careful examinations of the dissections, the reproductive systems oiF. latimarginata and F. cumingi were
indistinguishable in microscopic organization, and so a single
description is presented here for both species. The reproductive system
is composed of a) a single gonad, b) a renopericardial duct that
transport the gametes to the distal portion of the right kidney, it has
a gland attached to its inner wall and is connected by the nefrostome
to the pericardium; and c) the distal portion of the right kidney which
receives the gametes from the duct. The gametes leave the kidney
through its aperture toward the mantle cavity, and from there reaching
the exterior (Fig.1).
The renopericardial duct which carries the gametes from the gonad to
the right kidney is referred to from now on as the "genital duct".
Gonad: This organ is a multilobed
sac with variable morphology and size depending on the stage of
maturity of the individual. The color in males varies from white-cream
to yellow and in females is dark green; in both sexes it is well
separated from other organs of the visceral mass. The gonad occupies a
ventral position in the body cavity, below the digestive gland and
stomach, and is dorsal to the foot. In mature individuals it is
swollen, and extends from the posterior portion of the visceral cavity
toward its anterior end, occupying all the available space. The gonad
is covered with a cubical to low columnar epithelium, under which lies
a muscle/ connective tissue layer, from which projects septa of
connective tissue toward a common gonadic cavity. The germinal cell
line develops around the septa, interacting with the somatic cells in a
centrifugal organization towards the gonadic cavity (Figs. 2A, B).
Genital duct and kidney opening: Seen
in a transversal section genital duct arises in the upper right
mid-zone of the gonad and projects upward in the visceral cavity
parallel to the muscular wall of the limpet (Figs. 2C; 3A, C),
to which it is anchored by a thin mesentery. A gland is proximally
attached to the internal wall of the genital duct lumen (Figs. 2C, G,
H; 3A, C). Soon after the gland appears the nephrostome (Figs. 2D, I),
which is an aperture bearing a ciliated epithelium joining the duct
with the pericardial cavity at the level of the right auricle. Then the
duct continues its course below the muscular floor of the pericardium
toward the mid-region of the animal to open into the distal part of the
right kidney, near the base of the right kidney opening (Figs. 2F, K; 3B, D).
Distally, the duct near the kidney shows a widening of the lumen and
finger-like epithelial folds that fail to fill the lumen, with apparent
difference in length between both sexes (Figs. 2E, J; 3B).
The transversal section shows two types of simple epithelia all along
the genital duct, one above and one below, supported by a
muscular/connective tissue layer. The upper epithelium is observed as a
continuation of the epithelium which covers the gland associated with
the wall of the genital duct, while the lower epithelium is a
continuation of the gonadic wall isolating the gonad from the digestive
gland. The upper epithelium is formed of cylindrical cells having a
vesicular appearance, generally with basal nuclei, among which are
intercalated goblet cells. The epithelial cells release large
quantities of cytoplasmic vesicles and secretions into the lumen of the
genital duct. Prior to their detachment the vesicles remain connected
to the cells by cytoplasmic peduncles. Once the vesicles are released
they appear to break open in the lumen and release their contents. The
lower epithelium is also secretory, and is formed of flatter cells
which are more densely stained. The cells are smaller near the distal
portion of the duct and their borders are poorly defined. The histology
of the mid-portion of the genital duct in males of F. latimarginata and F. cumingi is shown in Figs. 3G, H.
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