Anatomy of finfish and shellfish (2+1)

Unit 13 - Mollusca

13.3.9. Sensory Organs
Eye
The two large eyes are unique in that superficially they resemble those of the vertebrates. However, when criti¬cally examined, they are found to be fundamentally different in structure and origin. Each eye has a transparent cornea a pigmented iris, a spherical lens, anterior and posterior chambers and retina with rods, etc. and can form a real image. This resemblance is a case of analogy or convergent evolution.
Statocysts
The two sac-like statocysts, probably organs of equilibrium, lie side by side embedded in the cephalic cartilages of the head, below the visceral ganglion.
Olfactory organ
Immediately behind each eye is a fold, the olfactory crest, the concavity behind which probably acts as an olfactory organ.