Neuroendocrine Control Mechanisms in Shell Formation

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Abstract
The brain of Helisoma duryi contains several neurodendocrine centres. Factors) present in the cerebral ganglia are thought to be involved in normal shell growth while neurosecretory substances present in the visceral ganglion are involved in the repair of damaged shell. In Lymnaea stagnalis a growth hormone is produced by the cerebral ganglion which stimulates periostracum formation and the calcification of the inner shell layer. The second effect is thought to occur through the action of a mantle edge calcium binding protein. In Helisoma, mantle collar is able to produce the periostracum in vitro. The presence of brain from a fast growing donor increases the amount of periostracum produced by a mantle collar from a slow growing animal. This effect is further enhanced by the removal of the lateral lobes. The periostracum produced by fast growing animals has a higher glycine content than that produced by slow growing snails. The presence of dorsal epithelial tissue enhances the incorporation of calcium into periostracum formed in vitro. These findings suggest that a single factor is present in the brain of fast growing Helisoma which modulates shell formation rates in vivo and periostracum formation in vitro.

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