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Primitive fish such as lampreys (Petromyzon marinus) have free nerve endings in the skin that respond to heat and mechanical pressure. However, behavioural reactions associated with nociception have not been recorded, and it is also difficult to determine whether the mechanoreceptors in lamprey are truly nociceptive-specific or simply pressure ...
Crayfish have peripheral nerve fibres [44] which are responsive to noxious stimuli. [42] Neurons functionally specialized for nociception have been documented in other invertebrates including the leech Hirudo medicinalis, the nematode Caenorhabditis elegans and the molluscs Aplysia californica and Cepaea nemoralis.
Although they have ears, many fish may not hear very well. Most fish have sensitive receptors that form the lateral line system, which detects gentle currents and vibrations, and senses the motion of nearby fish and prey. [1] Sharks can sense frequencies in the range of 25 to 50 Hz through their lateral line. [2] Fish orient themselves using ...
Two groups of invertebrates have notably complex brains: arthropods (insects, crustaceans, arachnids, and others) and modern cephalopods (octopuses, squid, cuttlefish) and other molluscs. [14] The brains of arthropods and cephalopods arise from twin parallel nerve cords that extend through the body of the animal.
Most fish have a homocercal tail, but it can be expressed in a variety of shapes. The tail fin can be rounded at the end, truncated (almost vertical edge, as in salmon), forked (ending in two prongs), emarginate (with a slight inward curve), or continuous (dorsal, caudal, and anal fins attached, as in eels).
While the electroreceptors in fish and amphibians evolved from mechanosensory lateral line organs, those of monotremes are based on cutaneous glands innervated by trigeminal nerves. The electroreceptors of monotremes consist of free nerve endings located in the mucous glands of the snout.
Although chitons lack osphradia, statocysts, and other sensory organs common to other molluscs, they do have numerous tactile nerve endings, especially on the girdle and within the mantle cavity. The order Lepidopleurida also have a pigmented sensory organ called the Schwabe organ. [26]
Many fish also have chemoreceptors that are responsible for extraordinary senses of taste and smell. Although they have ears, many fish may not hear very well. Most fish have sensitive receptors that form the lateral line system, which detects gentle currents and vibrations, and senses the motion of nearby fish and prey. [53]