There are many animals that make loud noises in the water, such as marine mammals, fish and crustaceans.However, no sound has been known in invertebrates such as annelids, which have a soft structure in most of their bodies.Kimurahanakagootohimegokai is a polychaete with a body length of about 2 cm, and is characterized by a round mouth attached to the front end of the body and long tentacles that grow from a translucent body.It lives on the Pacific coast of Japan and has a habit of living in the sponge of the sponge family.

　When this worm encounters another individual of the same species, it engages in a peculiar intraspecific struggle (mouse fighting) in which it talks to each other.At that time, an attack action (mouse attack) is performed in which the proboscis is momentarily projected on one side or each other and the opponent is flicked off.This time, at the same time as this attack, it was discovered by observing the inside of the aquarium that a single loud underwater sound was heard.

　The maximum sound pressure level of this underwater sound is 157 decibels (dB: 1 μPa sound pressure at a distance of 1 m is 0 dB).The frequency peaked around 6.9 kHz (kHz) and showed a wide range of values ​​up to 90 kHz and above.Furthermore, the mechanism of sound generation was inferred from the morphological changes of the pharynx that rapidly swelled during mouse attack and its muscle structure, but detailed verification is required in the future.

　This time, for the first time, we have shown that soft invertebrates, which were previously considered to be silent (cannot produce), can instantaneously produce loud underwater sounds.It is expected to contribute to the elucidation of the role and mechanism of pronunciation in invertebrates.

Paper information:[Current Biology] Remarkably loud snaps during mouth-fighting by a sponge-dwelling worm