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Cephalopods, as active marine predators, possess sensory organs specialized for use in aquatic conditions. [1] They have a camera-type eye which consists of an iris, a circular lens, vitreous cavity (eye gel), pigment cells, and photoreceptor cells that translate light from the light-sensitive retina into nerve signals which travel along the optic nerve to the brain. [2]
There are two sets of ocular tentacles: one set in front of the eye (pre-ocular) and one set behind the eye (post-ocular). The digital and labial tentacles are arrayed circularly around the mouth, with the digital tentacles forming the outermost ring and the labial tentacles in between the digital tentacles and the mouth.
There are many diseases known to cause ocular or visual changes. Diabetes , for example, is the leading cause of new cases of blindness in those aged 20–74, with ocular manifestations such as diabetic retinopathy and macular edema affecting up to 80% of those who have had the disease for 15 years or more.
Symptoms include “sensitivity to light, dizziness, pain behind the eyes, nausea, vomiting, and rash,” the CDC says, while more serious disease includes meningitis, encephalitis, and bleeding.
Additionally, the tentacles of the Nautilus also perform several sensory functions. Their ocular and preocular tentacles feature cilia, and operate as mechanoreceptors, while their digital tentacles have been hypothesised to feature a range of receptor cells. [15]
Scallops have up to 100 simple eyes. The molluscs have the widest variety of eye morphologies of any phylum, [1] and a large degree of variation in their function. Cephalopods such as octopus, squid, and cuttlefish have eyes as complex as those of vertebrates, while scallops have up to 100 simple eyes.
8 - nerve of the eye: Drawing of cross sections of the extracted tentacle (left) and constricted tentacle (right) with and eye of Helix pomatia. 1 - nerve of an eye 2 - 3 - 4 - eye 5 - tentacle ganglion 6 - epidermis 7 - 8 - nerve of an tentacle 9 - retractor muscle 10 - Well-developed lens eye of Eustrombus gigas on eyestalk has a black iris.
Throughout the world, the nautilus is captured to carve the elegantly shaped shells, and for their nacreous inner shell layer, a pearl substitute. [63] [64] [65] Mother-of-pearl or nacre, which lines some mollusc shells, is used to make organic jewellery. It has traditionally been inlaid into furniture and boxes, particularly in China.