This fantastic image from Plankton Portal shows one of the lethal predators of the plankton world, a chaetognath, more commonly referred to as an arrow worm. These sleek, streamlined creatures pray on other small organisms using hooked grasping spines that flank the mouth.  A hood arising from the neck region can be drawn over or away from the hunting spines, much like the action of sheathing and unsheathing a blade.

Hunt for some some arrow worms yourself on www.planktonportal.org