Ciekawostka: A shark is the only fish that can blink with both eyes

Evidence: 73 • authority: 72

Sharks are a group of elasmobranch cartilaginous fishes characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the division Selachii and are the sister group to the Batomorphi (rays and skates). Some sources extend the term "shark" as an informal category including extinct members of Chondrichthyes (cartilaginous fish) with a shark-like morphology, such as hybodonts. Shark-like chondrichthyans such as Cladoselache and Doliodus first appeared in the Devonian Period (419–359 million years), though some fossilized chondrichthyan-like scales are as old as the Late Ord…

Evidence: 73 • authority: 72

Vision is an important sensory system for most species of fish. Fish eyes are similar to the eyes of terrestrial vertebrates like birds and mammals, but have a more spherical lens. Birds and mammals (including humans) normally adjust focus by changing the shape of their lens, but fish normally adjust focus by moving the lens closer to or further from the retina. Fish retinas generally have both rod cells and cone cells (for scotopic and photopic vision), and most species have colour vision. Some fish can see ultraviolet and some are sensitive to polarised light. Among jawless fishes, the lamprey has well-developed eyes, while the hagfish has only primitive eyespots. The ancestors of modern…

Evidence: 59 • authority: 72

Blinking is a bodily function; it is a semi-autonomic rapid closing of the eyelid. A single blink consists of the closing of the eyelid or inactivation of the levator palpebrae superioris and the activation of the palpebral portion of the orbicularis oculi. It is an essential function of the eye that helps spread tears across and remove irritants from the surface of the cornea and conjunctiva. Blinking may have other functions since it occurs more often than necessary just to keep the eye lubricated. It may help with disengagement of attention; following blink onset, cortical activity decreases in the dorsal network and increases in the default-mode network, associated with internal process…

Evidence: 59 • authority: 92

The secret in their eyes: A review of the recessus orbitalis, a unique structure of flatfishes.. Flatfishes (Pleuronectiformes) are famous for having one of the most peculiar anatomical transformations in the animal kingdom, the ontogenetic migration of one eye from one side of the head to the other. But the eyes of flatfishes also carry a much lesser known but equally unique modification: an organ called the recessus orbitalis, which is responsible for projecting the eyeball above the level of the head, thus expanding their fields of vision. However, the morphology and distribution of the organ have never been thoroughly investigated. Previous studies reported only part of the recessus orb…

Evidence: 58 • authority: 80

Hedgehogs make both fish and fly eyes

Evidence: — • authority: 35