Arrow Worm
(Chaetognatha)
Chaetognatha, otherwise known as the arrow worm, are a predatory marine worm that feed on other planktonic animals.
There are around 120-125 species of arrow worm, most of which are planktonic.Their sizes range from 1mm to 15 cm and they have transparent skin. They also have a very distinct head that includes between four and fourteen hooked, grasping spines on the side of the head. The spines are used in hunting, and covered with a flexible hood arising from the neck region when the animal is swimming.
Arrow worms locate their prey by detecting vibrations produced by copepods and other zooplankton, they then use the spines and teeth at the front of the body to grab their victims and immobilize them with neurotoxins. Many chaetognath rise to surface waters at night and sinking downward during the day, possibly to avoid predators. These vertical movements are facilitated by ammonia-filled vacuolated cells in the trunk, which regulate buoyancy. Arrow worms lack circulatory, respiratory, and excretory organs. Cilia circulate fluid within each of the three body cavities, transporting nutrients and dissolved waste. Oxygen and carbon dioxide diffuse directly across the body wall.
Chaetognaths are hermaphrodites and reproduce sexually. Sperm in the tail cavity mature before the eggs in the trunk cavity. Sperm are released outside the body and cross-fertilization between individuals is typical, although some species may self-fertilize.
There are around 120-125 species of arrow worm, most of which are planktonic.Their sizes range from 1mm to 15 cm and they have transparent skin. They also have a very distinct head that includes between four and fourteen hooked, grasping spines on the side of the head. The spines are used in hunting, and covered with a flexible hood arising from the neck region when the animal is swimming.
Arrow worms locate their prey by detecting vibrations produced by copepods and other zooplankton, they then use the spines and teeth at the front of the body to grab their victims and immobilize them with neurotoxins. Many chaetognath rise to surface waters at night and sinking downward during the day, possibly to avoid predators. These vertical movements are facilitated by ammonia-filled vacuolated cells in the trunk, which regulate buoyancy. Arrow worms lack circulatory, respiratory, and excretory organs. Cilia circulate fluid within each of the three body cavities, transporting nutrients and dissolved waste. Oxygen and carbon dioxide diffuse directly across the body wall.
Chaetognaths are hermaphrodites and reproduce sexually. Sperm in the tail cavity mature before the eggs in the trunk cavity. Sperm are released outside the body and cross-fertilization between individuals is typical, although some species may self-fertilize.