Tunicates are, along with Vertebrates and cephalocordates, the three phylum of animals characterized by a nervous cord that runs through the body of the animal. Focusing on the group of Tunicates or also known as urochords, this is composed of approximately 2,800 species, and they are exclusively marine animals. Its name comes from the substance that secretes the wall of his body, the tunicin. A substance of celluloid type that gives them a support structure which we could consider as the skeleton of the animal. Under the external surface of the body wall, they have muscle bands oriented in a longitudinal direction, which allows them to retract the siphons and in this way they manage to pass water through their atrium (central body cavity). With this movement of water and filtering the organic particles present in the water, is how the Tunicates obtain their source of food.
There are Tunicates with different types of mobility, fixed species in the marine substrate (benthic), species that live in the water column (planktonic), as well as solitary and colonial species.
The body of Tunicates is divided into thorax and abdomen, and their nervous system is very reduced. They have a small cerebroid ganglion above the pharynx, from which they derive some nerves that go to the muscles of the rest of the body. It is during the larval stage, when Tunicates have a well-developed dorsal nerve cord. This nerve cord is lost when the specimens reach the adult stage.
In relation to the reproduction of Tunicates, these are hermaphroditic animals whose fertilization is usually external by releasing the gametes into the water, where they become part of the zooplankton until the larvae are deposited on the sea floor, in those benthic species.