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GASTROPODS REPRODUCTIVE SYSTEM Ansuman Panda M.F.Sc 1 st Year Adm. No.- FRM 02/16

Gastropods reproductive system

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Page 1: Gastropods reproductive system

GASTROPODS REPRODUCTIVE SYSTEM

Ansuman PandaM.F.Sc 1st Year

Adm. No.- FRM 02/16

Page 2: Gastropods reproductive system

INTERNAL ANATOMY

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.

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• 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.

INTRODUCTION

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GASTROPODS HAVING EXTERNAL FERTILIZATION

• 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.

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• 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.

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GASTROPODS HAVING INTERNAL FERTILIZATION

• 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 ).

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• 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).

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PROCESS 1.MATE FINDING

• 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).

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2.MATING AND FERTILIZATION

• 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.

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• The “dart shooting” 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.

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• 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.

3.RELEASE OF FERTILIZED EGGS

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ENVIRONMENTAL CONDITION INTERNAL STATES

CENTRAL NERVOUS SYSTEM

BAG CELLS

EGG LAYING HORMONE (E.L.H)

OVULATION

HORMONAL ACTION

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