Tunicates, previously known as Urochordata or urochordates, are members of the Tunicata, a subphylum of the phylum Chordata. They are marine filter feeders with a saclike morphology. In their respiration and feeding they take in water through an incurrent (or inhalant) siphon and expel the filtered water through an excurrent (or exhalant) siphon. Most adult tunicates are sessile and attached to rocks or similarly suitable surfaces on the ocean floor; others such as salps, doliolids and pyrosomes swim in the pelagic zone as adults. Various species are commonly known as sea squirts or sea pork.

The Tunicata apparently evolved in the early Cambrian period. Despite their simple appearance, they are a sister subphylum to the Vertebrata.

Like other chordates, tunicates have a notochord during their early development, but by the time they have completed their larval stages they have lost all myomeric segmentation throughout the body. As members of the Chordata they are true Coelomata with endoderm, ectoderm and mesoderm, but they do not develop very clear coelomic body-cavities if any at all. Whether they do or not, by the end of their larval development all that remain are the pericardial, renal, and gonadal cavities of the adults. Except for the heart, gonads, and pharynx (or branchial sac), the organs are enclosed in a membrane called an epicardium, which is surrounded by the jelly-like mesenchyme. Tunicates begin life in a mobile larval stage that resembles a tadpole. A minority of species, those in the Larvacea, retain the general larval form throughout life, but most Tunicata very rapidly settle down and attach themselves to a suitable surface, later developing into a barrel-like and usually sedentary adult form. The Thaliacea however, are pelagic throughout their lives. and their life cycles may be complex, as for example in the Salpida.

Mark Brian Sharman (born 2 January 1950) is a British broadcasting administrator.

He attended the John Port Grammar School in Etwall.

Sharman first worked as a journalist with the Derby Evening Telegraph and Birmingham Evening Mail before entering television journalism with ITV in 1976, where he edited coverage of Football World Cups and the Olympic Games. He later worked for BSkyB as deputy managing director of Sky Sports, helping to expand from one channel to four and creating Sky Sports News, before joining Channel 4 as controller of sport in 1998, where he wrested broadcasting rights for test cricket from the BBC. A year later he returned to BSkyB and became director of broadcasting, with responsibility for Sky One, Sky News and Sky Movies channels.

After a fourteen month sabbatical, he re-joined ITV as controller of sport in early 2005. Two years later Sharman was appointed as director of ITV's network and regional news, replacing the retiring Clive Jones, retaining his controller of sport role. He secured a notable coup in March 2007, when ITV, in a joint bid with Setanta Sports, successfully gained broadcasting rights for FA Cup matches and England national football team home games starting from August 2008. The BBC and Sky had previously held the rights since 2001. He stepped down from his position at the end of 2008.