Tonna perdix (Linnaeus, 1758)
120mm
Tonna perdix, the partridge tun, is moderately common exposed and hunting
on shallow reefs at night. They are known to eat sea cucumbers. The first photo
shows a small juvenile.
One night I caught one in the act
of attacking a Stichopus sea cucumber. Unfortunately, my camera was
stuck at the wrong focal distance, so the photo below is a bit unfocused. However,
it does show the large mouth emerging from the anterior end of the tun shell.
Just before this photo, it had expanded its mouth around about half of the sea
cucumber, starting at one end. The sea cucumber was frantically working its
tube feet and stretching the free portion of its body in an attempt to get away.
Suddenly, two strips of the cucumber's thick outer skin, one strip on each side,
detached from the cucumber's body. The portion of the cucumber that had been
in the tun's mouth then sprang out like a contracting rubber band that had been
stretched, which is the moment the photo below was taken. As soon as the cucumber
was out of the tun's mouth, it released its tube feet from the bottom and was
pushed away from the predator by a surge in the water. The prey escaped, and
presumably was able to regenerate its lost skin, which is shown in the following
photo below.
Here are the two flaps of thick
skin that the sea cucumber sacrificed in order to slip out of the mouth of the
attacking tun shell. The tun was left only with these in its mouth, and apparently
they are not very edible; the tun dropped them and wandererd off to look for
easier prey. Note that some sea cucumber tube feet were also sacrificed and
are still holding onto the substrate from the lower flap.
Created
9 January 2021
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