The secret of the 'left hand' of the sea snail

The left hand snail (left) seems to have more survival advantage than the right hand snail, because crabs cannot stick to them. ( Photo: BBC ) The snails with shells rolled to the left have a great survival advantage, because the enemy must give up on eating them.

The conclusion is published by American scientists in the Royal Society's Biology Letters. To distinguish the left or right hand clamshell, hold it in your hand and point the tip towards the front, the snail's mouth is facing you. If the mouth opens on the right, it is the right-hand clamshell and vice versa, if the mouth opens to the left, it is the left-hand clamshell.

The scientists examined the shells of the snails (snail-like sea snail) and cones that were the prey of Calappa flammea . They found that the crabs could not open the spiral shells to the left because it only had one tool to turn the lid on the top right, so the crabs ignored those screws.

" Crab has a special tool on it, which is used as a can opener. Therefore, imagine using a can opener for the right-handed person with your left hand - you will find it difficult. towel to do that, "said Gregory Dietl from Yale University.

Calappa flammea crab

Dietl and colleagues studied 11 pairs of shells and cones dating from 1.5 to 2.5 million years ago along with those that exist today, in both left and right hands. .

10 out of 11 pairs showed a lot of scars on the right arm, indicating that the crabs attacked them more than the left hand.

Normally, the crab will clutch the snail shell so that the tip is directed away from its body. With the right-hand shells, that means opening the screw cap to the right, and the special tool on the crab's shell can attack inside. But with a left hand screw, or a crab will have to open the lid on the left, or it must grab the prey in the snail-tip posture towards the body. Both of these solutions seem too complicated, and the crab will act like a vegetarian going into the butcher's counter, and leaves.

The evolutionary question here is why the left hand screw is so rare - some even become extinct - if that advantage makes it easier for them to escape the crab's clutches.

Perhaps if the left-hand sea snail group becomes more popular, crabs will evolve the body structure or hunting technique, and the advantage of the left hand snail will disappear.

T. An