An octopus is known for its round squishy body, three hearts, shifting skin, and eight flexible tentacles full of suckers. Its whole body helps it survive in the wild by camouflaging to remain hidden while stealthily exploring their surroundings with their limbs that each seem to have a mind of its own.
Unknown to many, these tentacles are not only used to reach their prey but also allows them to taste it. The suckers in each tentacle turn out to possess the touch-taste ability that enables them to capture a sensory map of their surroundings.
Molecular biologist Lena van Giesen and colleagues from Harvard University have identified these chemosensory cells in the sucker's skin of a California two-spot octopus that detect molecules like how the olfactory and gustatory cells do. They published their findings in Cell.
Taste Cells in the Suckers of an Octopus
Scientists from Harvard University in Cambridge, Massachusetts analyzed how octopuses behaved when their suckers touched an object. They found that an octopus would ignore inanimate objects and would probe the sea using their limbs. Once they find their prey, they would wrap it using their limbs which confirms the notion that an octopus uses their suckers to detect their food.
Previous studies have shown that the chemotactile receptors on the surface of the suckers respond to specific molecules, such as terpenoids, which are released by several marine animals as a defense mechanism.
When the taste cells bind with these chemicals, it sends an electrical signal that passes chemical and tactile information to the nervous system of the octopus.
Moreover, the suckers of the octopus also contain more familiar mechanosensory cells that only fire during the start of contact, according to Science Alert. This type of signalling tells the octopus that they are touching inanimate objects or squirming prey.
"We find octopuses explore their environment using stereotypical touch motions that are distinctly modified by contact with different [molecules that trigger the chemotactile receptors]," the researchers said.
They used a method called transcriptomics in looking at what proteins are expressed by the genes of specific sucker cells. The team found that some of the chemotactile cells are strongly activated to crab and fish extract. Also, these sucker cells trigger a rapid retreat at repulsive flavors that could hint at danger.
The researchers also observed how the ink of the octopus shuts down the ability of the suckers to taste. The findings of their study suggest that chemosensation could also be present in other aquatic animals by detecting soluble molecules that are contact-dependent as well.
Octopus Has Eight Dexterous Arm-Tongues
According to biologist Rebecca Tarvin from the University of California, who was not part of the study, the genes for chemotactile receptors are found across the octopus species, but some cephalopods like squids do not use their suckers the way a California two-spot octopus does.
Molecular biologist Nicholas Bellono said that their team is now exploring how this unique sensorimotor system evolved in octopus as they try to answer questions regarding its evolution and physiology.
The researchers believe that that the "mini" brains in the octopus arms have an exceptional ability to filter information from highly specialized receptors which might explain why two-thirds of its neurons are on its arms.
Essentially, an octopus has eight dexterous arm-tongues that they use to feel and taste their food without using their main body.
Read More: Deadly Blue-Ringed Octopus Spotted in Sydney Harbour
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