HMCS Max Bernays Pre-Deployment Brief (May 2024).pptx
Gastropods reproductive system
1.
2. Two gonads are located next to the coelom and release ova or
sperm into it. The kidneys extract them from the coelom and
release them into the mantle cavity from which they can reach
the water or land.
3. • If we will study the reproductive biology of
some gastropods, we can find that some
gastropods use internal fertilization and/or are
hermaphrodites, functioning as both sexes
and some are external fertilization.
• The marine gastropods are commonly dioecius
i.e.-both the sexes are separated(except-
family onchidiidae and siphonnidae). But the
terrestrial gastropods are generally
hermophrodites.
4. • The process starts when both the male and
female releases the sperm and eggs into the
water respectively.
• Fertilization to take place outside the female.
The fertilized egg hatches into a free-
swimming form called trochophore larva.
5. • Upon the expansion of the ciliary girdle of the
trochophore larva into large, heavily ciliated
lobes (vela), the larva, called a veliger. Food
consists of diatoms (an algae group) and other
small plankton collected by ciliary currents of
the velum and channeled by the currents into
the mouth.
• Then the meta-morphosis of veliger occurs
and it becomes a post larvae and then a
juvenile and then an adult.
6.
7. • In simultaneous hermaphrodites, each animal performs only
one role in a given mating, with role preferences varying
within and between individuals. After completing one
unilateral sperm donation, the partners often switch roles in a
second mating.
E.g- opisthobranchs (Aplysia, Cliona, Cavolina, Doris, etc) and
The pond snail(Lymnaea ).
8. • Animals such as Aplysia californica, which have their male and
female genitalia located on different parts of the body and
normally mate unilaterally, can form daisy chains which may
contain as many as six mating individuals. The first individual
in the chain acts only as a male, the last individual acts only as
a female, and all animals in between act as female to one
partner and male to a second partner.
• Numerous species of freshwater gastropods contain
hermaphroditic individuals that lack penes (aphally). Such
animals reproduce either by outcrossing as females or by
using their own sperm to fertilize their own eggs (selfing).
9. • Potential mates must be located and identified
using the chemical senses (olfaction and contact
sensations) because gastropods have no sense of
hearing and little or no vision. Sea slugs in the
genus Aplysia release a bouquet of pheromones
when laying eggs, and these substances attract
conspecifics that may then mate with the egg-
laying individual. Several of these pheromones
have been identified and sequenced; they have
been given the names “attractin”, “seducin”,
"enticin", etc. (Painter et al., 2004).
10. • The receiver, receives sperm and can
store for many months to years before it
is used to fertilize eggs. Meanwhile, the
receiving individual may mate with
additional sperm donors. When the
multiply mated individual eventually
fertilizes its eggs, it will generally select
sperm at random (as in a raffle) from the
stored pool.
11. • The “ ” is a phenomena seen in
terrestrial gastropods where the donor expel the
dart (solid and has a sharp tip; it is made of pure
calcium carbonate crystals) from the genital pore
in the later stages of courtship and it often, but
not always, penetrates into the flesh of the mate.
It is observed that more of the shooter’s sperm
becoming stored by the receiving mate compared
to cases where the dart misses. This is because of
the mucus that clings to the surface of the dart.
This mucus contain a peptide and enhance the
survival of the shooter's sperm.
12.
13. • Aquatic gastropods generally deposit their eggs in
gelatinous masses that are attached to a hard
surface. Opisthobranchs lay huge numbers of
fertilized eggs. For example, a single specimen
of Aplysia californica was observed depositing
one mass that contained 140,000 eggs (Kandel,
1979). Moreover, during the spawning season, an
individual Aplysia californica will typically lay eggs
at intervals of 1 or 2 days.
• In such species the trochophore and veliger
stages are passed within an egg and it releases a
crawling gastropod after hatching.
