Sea Squirts (Ascidians) live on the floor of the ocean and are immobile filter feeders. They are closely related to vertebrates rather than coral or sponges even with their plant-like appearance. With over three thousand known species of sea squirt, they can be found all around the world; however, the largest number of them prefers warmer tropical water. These amazing little creatures come in various sizes, colors and shapes with a solid shape and without a skeleton. The majority of sea squirts have a cylinder shape with a few being bell or round shaped with a membrane of a few cell's thickness for protection.
The body of the sea squirt has an outside covering of a smooth but rigid tunic that is made up of cellulose - like material known as tunicin as well as proteins and calcium salts. These unusual creatures have their own blood supply because the tunic is made up of living tissue. Some species of sea squirt individuals will fuse together making a single structure of a colony of sea squirts.
Because they are filter feeders, they have slits in their membranes known as an oral siphon in order to bring in water into their atrium (a special water chamber) with food nutrients for feeding. They are able to release the excess water and wastes completing the process through the atrial siphon. The really large sea squirts are able to trap and ingest small fish or jellyfish because the larger species have a rod like appendage attached that allows them to catch the food that is passing by. For food digestion, the animal has an esophagus that runs down to the stomach, and into the abdomen where enzymes are secreted to digest the food. Waste is discarded through an intestine that runs parallel to the esophagus up from the stomach that opens into cloacae through a small rectum and anus.
At a very young age sea squirts attach themselves to objects making them easy prey for snails, eels, fish, crustaceans, birds and sea otters. In certain parts around the world which includes Japan, Chile and Europe, Sea squirts are eaten by humans where they are called sea violet.
Sea squirts are equipped with both male and female reproductive organs. They release both eggs and sperm in the water which becomes fertilized as well as part of the plankton. When the larvae hatch from the eggs, it works its way to the ocean beds and finds something to attach itself to like rocks or shells. When these animals are removed from the water, it often violently forces out water from their siphons thus giving it the common name of sea squirt.