The animals belonging to the subphylum Urochordata, also known as urochordates ortunicated, are sessile animals that live attached to rocks or other substrates in the world's oceans. They are animals that present notochord only in their larval stage and can be found living alone or in colonies. sea squirts.
The animals of this subphylum have the body covered by a tunica constituted by tunicine, cellulose-like substance. In the tunic we can find two openings called inhalant siphon and exhalant siphon.
The adults of the urochordates live attached to rocks or other substrates
at the bottom of the inhalant siphon, also called oral siphon, we find the animal's mouth – it is through this structure that sea water penetrates into the urochordate's body. When water is inhaled along with food particles, the food is retained in the gill slits. and sent to the stomach through the endostyle, to then be taken to the intestine and then to the anus. The anus in these animals opens into a cavity called the
atrium, and it is in this cavity that all excreta are eliminated. Through the exhaling siphon, in addition to these residues, gametes and water are also eliminated.The urochordate animals present circulatory system partially open, with the heart located in the ventral part of the body, pumping blood (hemolymph) to the pharynx, where it is oxygenated in the branchial clefts and sent to the rest of the body. The circulatory system of these animals works sometimes in one direction, sometimes in the other. This is because the heart pumps blood to the gill clefts, and after a few contractions, the heart stops and begins to pump blood in the opposite direction, towards the organs of the body.
In the larval stage, the urochordates have the notochord in the tail, whereas in the adult stage these animals have only one brain ganglion which is located between the two siphons. From the brain ganglion, several nerves come out to all regions of the animal's body.
All urochordate species have sexual reproduction, most of them monoecious, but we can also find species that perform asexual reproduction by budding, originating colonies. During reproduction, the urochordate eliminate their gametes in the water, where fertilization will take place. From the zygote, a free-swimming larva develops which, after some time swimming through the waters, attaches to a substrate and begins its metamorphosis, a period in which the tail and the notochord will disappear.
By Paula Louredo
Graduated in Biology
