Biology of Archachatina SHITTU, O. Zoology, Unilorin ZLY 201

Description of the Shell

Shell Structure & Formation Fig. 16.5a

Body Shell Plan

The process of torsion

Coiling in Gastropoda Early gastropods had all the whorls lined in a single plane i.e. had a planospiral shell and were bilaterally symmetrical. Today, gastropods exhibits a conispiral shape i.e. each succeeding wall is at the side of the preceding one. With conispiral shape, the animal had to redistribute it weight by shifting the shell upward and posteriorly.

Coiling in Gastropoda The shell axis now appear oblique to the longitudinal axis of the foot. Weight and main body whorl pressed on the right side of the mantle cavity. Loss of the gill, auricle & right kidney leading to bilateral asymmetry. Fouling eventually avoided as water enters the left and lives by the right through the anus and nephridiopore Today, gastropods exhibits a conispiral shape i.e. each succeeding wall is at the side of the preceding one. With conispiral shape, the animal had to redistribute it weight by shifting the shell upward and posteriorly.

Ctenidia loss in Gastropoda The Pulmonata show some detorsion, therefore has lost their ctenidia thereby making the vascularized mantle wall assuming a lung function by contraction of the mantle floor. The anus and nephridiopore opens near the pneumostome expelling wastes via water from the lungs. Archachatina has two pairs of tentacles with the posterior one bearing the eyes. Position of the eye

Archachatina Anatomy Position of the lung showing pneumostome

Archachatina Anatomy They have a single nephridium (kidney). The circulatory and nervous system are well developed. The nervous system has three pairs of ganglia connected by nerves. Sense organ includes eyes (photoreceptors, statocysts, tactile organs & chemoreceptors) The eye cup contain a lens covered with a cornea. The osphradium situated at the base of the incurrent siphon is sensory in function (chemoreceptor)

Archachatina Anatomy Radula This is a rasping, protrusible, tongue like organ. It is a ribbon-like membrane on which rows of tiny teeth pointing backward are mounted. Complex muscles move the radula and odontophore in and out so that the membrane rotates over the cartilage tips (250,000). The radula rasp off fine food particles and conveys it towards the digestive tract. The pattern and number of teeth in a row determines the speciation.

Reproduction in Archachatina They are monoecious, undergoing intracapsular(direct) development instead. Fertilization is internal. They are ovoviviparous, brooding their eggs in the pallial oviduct Adult snails Mating Shedding of Eggs

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