Tunicate

Tunicate

The Tunicate (also known as Urochordata or sea squirts) is a subphylum of marine invertebrate animals, a part of the Chordata phylum, which also includes the vertebrates (animals with backbones). Tunicates are named for their unique outer covering or "tunic," which is made of a cellulose-like substance.

Anatomy

Tunicates are characterized by a tough outer "tunic" made of the polysaccharide tunicin. The body of a tunicate is composed of a trunk and two siphons, through which water enters and exits the body. The interior of a tunicate is composed of a pharynx, which is used for feeding and respiration, and a digestive tract.

Life Cycle

Tunicates have a complex life cycle with a larval stage, which is markedly different from their adult form. The larvae are free-swimming and possess a structure, the notochord, which is characteristic of chordates. The adults are sessile (non-moving) and have lost the notochord.

Classification

Tunicates are classified into three classes: Ascidiacea (sea squirts), Thaliacea, and Appendicularia (larvaceans). The Ascidiacea are the most diverse and numerous, while the Thaliacea and Appendicularia are less common.

Ecology

Tunicates are found in a wide range of marine environments, from the intertidal zone to the deep sea. They are filter feeders, capturing plankton and other small organisms from the water column.

Evolution

Tunicates are of interest in the study of evolution, as they are the closest living relatives of the vertebrates. Despite their simple adult form, their complex life cycle and larval stage provide important clues about the origins of the vertebrates.

See Also

• Chordata
• Invertebrate
• Marine biology

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