When chaetognaths swim
they cover their grasping spines with a hood, making them more streamlined
and allowing for faster movements. Swimming in chaetognaths is accomplished
by bending the head region back towards the tail in a flicking movement
which cause the sleek worm to glide forward. Fins are also important in
the organisms locomotion. Posterior fins are used to overcome sinking and
facilitate stablization of the swimming motion. The tail fin may help to
rocket the organism through the water.
Reproduction in chaetognaths is unique. All chaetognaths are hermaphroditic, meaning they have both male and female parts. Eggs are formed in the trunk region of the body, whereas the sperm develop in the tail portion. Sperm can sometimes be seen swimming inside the tail portion of the body. One species courts by grasping the potential mate with its head spines. It is thought that several species undergo a similiar courtship in order to prevent themselves from being interpreted as a tasty meal.
During the courtship the sperm must rupture through an outpocketing of the body and travel down along the partners body into the female opening. It is not known how sperm find their way from the male into the female opening. It is thought that some species are capable of self fertilization (egg and sperm come together from the same individual), which is rare in other invertebrates.
After fertilization, the eggs are secreted in a slime that is either dropped in the water column, brooded (kept on the body until metamorphosis), or placed on vegetation. Placing the eggs on vegetation is thought to be advantagous as it keeps the eggs from drifting away from the coastal planktonic environment.