Archerfishes are well known for their ability to shoot a jet of water at insects in overhanging branches. So how do they do it?
Adaptations to the mouth give archerfishes their impressive expectorating ability. A deep groove runs along the roof of the mouth (see image to the right). A ridge along the top of the tongue fits into this groove. When an archerfish shoots a jet of water, it raises its tongue against the roof of the mouth forming a tube. The gill covers are then quickly closed, forcing water along the tube. The tip of the tongue acts as a valve. The BBC filmclip below shows archerfish in action along with a velvet worm firing streams of glue.