Vertebrate Zoology - V. M. Konstantinov 2011

Chordates
Tunicates, or Urochordates

General characteristics

The subphylum comprises five classes: Ascidiacea, Pyrosomacea, Thaliacea (Salpida and Doliolida), and Appendicularia.

This is a relatively diverse group of exclusively marine animals (comprising about 1,500 species) that differ sharply from other Chordates in that, as adults, most representatives lack a notochord and a neural tube. During the larval stage, all the key diagnostic Features of the phylum are well-developed in tunicates.

Many tunicate species lead a sessile lifestyle, inhabiting the seafloor either solitarily or in colonies; There are also free-swimming pelagic species inhabiting tropical and subtropical waters. They have a broad vertical distribution, ranging from the surface waters down to depths exceeding 5,000 meters. Within Russia, they are absent from the Caspian and Azov Seas. In total, about 150 species inhabit Russia's territorial waters.

The body shape of tunicates is sac-like or barrel-shaped. Externally, the body is enclosed in a specialized, often thick covering known as the tunic, which has a gelatinous or cartilaginous consistency. The tunic presumably evolved in connection with the transition to a sessile lifestyle and serves a protective function. Another adaptation to these environmental conditions is likely The ability to reproduce not only sexually, but also asexually via budding. Tunicates are hermaphroditic.

The Structural Features of tunicates are examined in greater detail below using a solitary ascidian as an example, as studying its ontogeny is crucial for establishing the potential phylogenetic relationships of chordates.



Last update: 13/08/2026

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