Tunicate

Marine invertebrate animals of the subphylum Tunicata

Tunicates are marine invertebrate animals that belong to the subphylum Tunicata, also known as Urochordata. They are part of the phylum Chordata, which also includes vertebrates. Tunicates are characterized by their sac-like body structure and a tough outer covering called a "tunic," which is made of a cellulose-like carbohydrate.

Anatomy and Physiology

Tunicates exhibit a wide range of body forms, but they generally have a simple body plan. The adult tunicate body is typically composed of a siphon system, a pharynx with gill slits, and a digestive tract. The tunic, which gives them their name, is secreted by the epidermis and provides protection.

Larval Stage

Tunicates have a distinct larval stage that resembles a tadpole and possesses a notochord, a dorsal nerve cord, and a post-anal tail, which are characteristic features of chordates. This larval stage is free-swimming and is crucial for dispersal.

Adult Stage

In most tunicates, the adult stage is sessile, meaning they attach to a substrate such as rocks or the ocean floor. However, some tunicates, like those in the class Thaliacea, remain pelagic and free-floating throughout their life.

Reproduction

Tunicates can reproduce both sexually and asexually. Sexual reproduction involves the release of sperm and eggs into the water column, where fertilization occurs. Asexual reproduction is common in colonial tunicates, where budding leads to the formation of new individuals.

Ecology

Tunicates are found in oceans worldwide, from shallow waters to the deep sea. They play a significant role in marine ecosystems as filter feeders, consuming plankton and organic particles suspended in the water. This feeding activity helps maintain water quality and clarity.

Classification

Tunicates are divided into three main classes:

• Ascidiacea - Commonly known as sea squirts, these are mostly sessile tunicates that attach to substrates.
• Thaliacea - Includes free-floating tunicates such as salps, which form large colonies.
• Appendicularia - Also known as larvaceans, these tunicates retain their larval characteristics throughout life.

Importance to Humans

Tunicates are of interest to scientists due to their evolutionary relationship to vertebrates. They are also studied for their potential in biotechnology and medicine, as some species produce bioactive compounds with pharmaceutical applications.

Gallery

File:Tunicate ascidian.jpg

A colonial ascidian tunicate

File:Salp chain.jpg

A chain of salps, a type of thaliacean tunicate

Related pages

• Chordate
• Invertebrate
• Marine biology