Prey detection by Chaetognatha via a vibration sense

Chaetognaths (arrow worms) have two types of tufts along the body, not previously distinguished. The bristles seen in life are non-sensory processes of epithelial cells. The ciliary tufts visible in sections are groups of sensory neurons each of which bears a non-motile cilium at the tip of its dendrite. The high sensitivity to vibrations set up by a nearby oscillating source in the dark is attributed to the non-motile cilia. The example analysed, Spadella cephaloptera, makes an accurate feeding movement towards any source vibrating at 9 to 20 c/s with an amplitude of 100 to 500 μm at a distance of 1 to 3 mm. Other vibrations are ignored or cause an escape response.