Anatomy of finfish and shellfish

Unit 13 - Mollusca

13.2.15. Sense Organs
The sense organs are poorly developed due to slow, sluggish and sedentary habits. The eyes and tentacles are altogether absent.
The main sensory parts are— (1) statocysts, (2) osphradium and (3) scattered epithelial nerve sensory cells.
Statocysts
The foot contains a pair of minute hollow vesicies, the statocysts, one close to each pedal ganglion. They are innervated by the cerebro-pedal connectives. Statocyst is lined by sensory cells and contains a mass of lime, called a statolith, the movement of which stimulates the sensory cells. The statocysts are thought to be organs of equilibrium.

Fig. 20. Anodonta. T.S. Statocyst
Osphradium
At the base of gills and on the surface over the visceral ganglia, is a pair of dark yellow patches of sensory epithelial cells forming the osphradium, which is probably used for testing the chemical nature of the water entering the mantle cavity through the inhalent siphon.
Sensory cells
The edges of the mantle-lobes are provided with scattered sensory cells, especially abundant on the inhalent siphon. They probably respond to touch (tactile) and also seera to be sensitive to light (photoreceptors).

Fig. 20. Anodonta. T.S. Statocyst