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Cephalopods have large, well-developed brains, [8] [9] [10] and their brain-to-body mass ratio is the largest among the invertebrates, falling between that of endothermic and ectothermic vertebrates. [11] The nervous system of cephalopods is the most complex of all invertebrates.
The head includes the mouth and brain. The foot has evolved into a set of flexible, prehensile appendages, known as "arms", that surround the mouth and are attached to each other near their base by a webbed structure. [26] The arms can be described based on side and sequence position (such as L1, R1, L2, R2) and divided into four pairs.
Cephalopod limbs bear numerous suckers along their ventral surface as in octopus, squid and cuttlefish arms and in clusters at the ends of the tentacles (if present), as in squid and cuttlefish. [9] Each sucker is usually circular and bowl-like and has two distinct parts: an outer shallow cavity called an infundibulum and a central hollow ...
Squids do not have the longitudinal muscles that octopus do. Instead, they have a tunic. [81] This tunic is made of layers of collagen and it surrounds the top and the bottom of the mantle. Because they are made of collagen and not muscle, the tunics are rigid bodies that are much stronger than the muscle counterparts.
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Researchers have identified an extinct vampire squid-like creature that is the first of its kind with 10 functional arms. The earliest known relative of octopuses and vampire squid has been named ...
The yellow papillae flatworm, Thysanozoon nigropapillosum, is somewhat cephalized, with a distinct head end (at right) which has pseudotentacles and an eyespot. The Platyhelminthes (flatworms) have a more complex nervous system than the Acoela, and are lightly cephalized, for instance having an eyespot above the brain, near the front end. [4]
These selective pressures may explain why the octopus’ brain is the largest of any invertebrate and vastly larger and more sophisticated than the clams. There’s another concept that comes into ...