Themolluscs have the widest variety ofeye morphologies of anyphylum,[1] and a large degree of variation in their function.Cephalopods such asoctopus,squid, andcuttlefish have eyes as complex as those of vertebrates, whilescallops have up to 100simple eyes.[2]
There are between seven and eleven distinct eye types in molluscs.[3] Molluscs have eyes of all levels of complexity, from the pit eyes of manygastropods, to the pinhole eyes of theNautilus, to the lensed eyes of the othercephalopods. Compound eyes are present in some bivalves, and reflective 'mirrors' have been innovated by other lineages such asscallops.[1] As well as varying in complexity, the eyes of molluscs span a huge range in size; they may be from 20 μm (0.0008 in) to 27 cm (11 in) across.[1]
Gastropods andcephalopods have paired eyes on their heads (and sometimes tails),[1] but many molluscs do not have clear head regions in which to locate the eyes. Consequently, many molluscs may have a multitude of eyes in more unlikely places, such as along the edge of their shell.[1]Chitons have a dispersed network oftiny eyes over the surface of their shells which may act together as a compound eye.[1]Many gastropods have stalked eyes; the eye can be retracted into the stalk itself in the presence of danger.[1]
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