The California two-point squid
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Octopuses can taste their prey by "licking" it with their arms before they are eaten. The researchers say that the eight appendages of the cephalopods correspond to the tongues with "hands" and "brain".
Octopus arms are lined with suction cups that contain cells for neural processing of touch and taste signals. These enable them to determine whether an animal is good to eat or whether it is poisonous, says Nicholas Bellono of Harvard University. This is especially useful as octopuses have a tendency to hunt "blind" and stick their limbs into holes and crevices to find hidden prey.
Bellono and colleagues examined the suction cells of California two-point squid (Octopus bimaculoides) microscopically and at the molecular level and found that some respond to touch and others to the "taste" of chemicals in the water, the sensory branching being typical Cells.
They then used electrophysiology, which measures the electrical activity of cells, to test how sensitive the taste and touch receptors on the suction cups were to different types of aromas and smells, respectively. Scientists found that the receptors responded to water-soluble chemicals like bitter chloroquine, as well as chemicals that don't dissolve well in water, such as those emitted by poisonous prey, Bellono says.
Many marine animals, including octopus, have olfactory organs that are likely to detect chemicals that are water soluble and possibly some sparingly soluble chemicals. However, it is usually believed that this "underwater smell" occurs over distance in the water, just as the noses work over distance in the air. Poorly soluble molecules require a close range for detection, which is facilitated by direct contact, similar to how tongues work.
Octopuses actually have a tongue-like organ in their mouth called the radula that cuts and scratches prey, especially shellfish. Still, it doesn't seem to be tasty. The radula “looks more like teeth,” says Bellono.
So far, the taste / touch receptors seem to be "specific to the suction cups," says Bellono.
Journal reference: Cell, DOI: 10.1016 / j.cell.2020.09.008
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