Molluscs {cephalopod} (Cephalopoda) include squid, cuttlefish, octopus, and nautilus.
evolution
Cephalopods began 500,000,000 years ago.
anatomy
Head and foot combine. Eight tentacles in octopus, or ten tentacles in squid, have suckers. Two beaks are in mouth. Mantle can fill with water and eject water for jet propulsion movement after mantle receives signals from giant axons. Ink sac squirts to confuse enemies.
anatomy: shell
Cephalopods have little or no shell, as in squid and octopus, or chambered shells, as in nautilus. Nautilus secretes gas into chambers, to float.
anatomy: eye
Eyes develop from skin folds. Octopus rapidly learns visual and tactile discriminations by trial-and-error and can learn complex landscape, using same visual cues that people do. Nautilus eyes are pinholes, with statocysts and eye muscles. Other cephalopods have eyes with photoreceptors in microvilli at right angles, to detect plane-polarized light.
anatomy: brain
Statocysts can detect three-dimensional movement. A cephalopod brain region acts like cerebellum. Cephalopods have visual-memory brain structures. They have no myelin.
blood
Hemocyanin copper protein, which has low oxygen-carrying capacity, causes green blood.
Biological Sciences>Zoology>Kinds>Mollusc>Cephalopod
4-Zoology-Kinds-Mollusc-Cephalopod
Outline of Knowledge Database Home Page
Description of Outline of Knowledge Database
Date Modified: 2022.0224