![]() ![]() All chordates are based on a bilateral body plan.This means that, during the embryo development stage, the anus forms before the mouth. There are soft constraints that separate chordates from other biological lineages, but are not part of the formal definition: It also stores iodine, and may be a precursor of the vertebrate thyroid gland. In filter-feeding species it produces mucus to gather food particles, which helps in transporting food to the esophagus. This is a groove in the ventral wall of the pharynx. In some chordates such as humans, this is only present in the embryonic stage. A muscular tail that extends backwards behind the anus. In tetrapods, they are only present during embryonic stages of the development. In fish, the slits are modified to form gills, but in some other chordates they are part of a filter-feeding system that extracts particles of food from the water in which the animals live. ![]() The pharynx is the part of the throat immediately behind the mouth. In fish and other vertebrates, this develops into the spinal cord, the main communications trunk of the nervous system. Among the vertebrate sub-group of chordates the notochord develops into the spine, and in wholly aquatic species this helps the animal to swim by flexing its tail.
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