Leocratides kimuraorum (Japanese: Kimura-hanakago-otohime-gokai) is a species of marine worm belonging to Hesionidae,[1] which is known for the intensity of its intraspecific fighting.

This bristle worm species lives off the coast of Japan, inside sponges 85–169 metres (279–554 ft) deep.

[4] Other members of the genus Leocratides — worms inhabiting Aphrocallistes sponges — include L. ehlersi and L. filamentosus.

In life, the worm is transparent, with ring-shaped integument (scaly ridges) along the back, and discontinuous brown stripe markings.

During these encounters, the pharynx muscles expand rapidly, forming a cavitation bubble that then collapses and produces a loud "pop" while the worms launch into each other.