What are worms arrows?
worms are a highly unusual group of "worms" that are clearly not related to any other worm or other animal. They create their own phylum, chaetognatha, one animal phylum among about 37 in total. As far as numbers are concerned, the arrow worms are among the most abundant phylo on the planet - only arthropods, non -plates and several others will even approach. The wide worms inhabit the water column, usually in the pelagic zone, up to 200 m (656 ft), where most plankton live, even if they can be found as deep as the lower mesoplagic zone, 1000 m (3 280 ft). Together with copepods, the crustaceans are "insects of the sea", Chaetognaths are the most common form of plankton. Long hair is a reference to a dependent, chitinous grip of the spine found in pairs on their head, their primary hunting tool. During swimming, the spine is held in the hood. The screws are carnivores, consume any plankton they can find. Their size is about 3-5 cm (1-2 inches), nail length, although some individuals can be up to 10 cm (4 inches). In 20 rOnly about 120 kinds of chaetognaths are known, but despite the low number of species, their abundance for the human mind is difficult to imagine.
We can provide a rough estimate of the number of worms with darts around the world. The measured densities range from about 1 to 30 individuals per meter of cubic meter of illuminated water, with a diameter of five. Given that the world ocean has an area of about 340 million square kilometers, without Arctic and Antarctic waters and the pelagic zone is 200 m deep, we can estimate a total of approximately 340 billion, which is probably correct. Interestingly, it also allows you to estimate that the human biomass exceeds the bio -bio -bio.
Because Chaetognaths are transparent, scientists can place them under the microscope and observe the whole process of digestion. They estimate that the worms eat arrows between 3 and 50 prey per day, including numerous larvae, braopod and other small crustaceans and otherWorms with arrows. They puncture the thin protective tissue layers of these organisms with their chitin spine and then injection toxins such as neurotoxin tetrodotoxin to cause death.
The arrow worms are considered a good model for early bilaterian. It is assumed that basal schedules (one of the two main divisions of animals) are, although the elements of their embryological development resemble deuterostomes. This is considered because they represent a very early branching of deuterostomes. This event probably appeared extremely long ago, during the Ediacaran period. Molecular and morphological studies have indicated that Chaetognaths are most closely related to nematodes, and in fact it may be related to the common ancestor of the ecdysozoans (a group that includes every animal that casts its cuticle).