Urochordata

Urochordata

Urochordata (pronounced: yoo-roh-kor-da-ta), also known as Tunicata (pronounced: too-ni-ca-ta), is a subphylum of the phylum Chordata. The name "Urochordata" comes from the Greek words "oura" meaning tail and "khordē" meaning string or cord.

Definition

Urochordata are a group of invertebrates that are closely related to vertebrates. They are marine animals and include species such as sea squirts, salps, and larvaceans. The defining characteristic of Urochordata is the presence of a notochord, a flexible rod-like structure, during some stage of their life cycle.

Anatomy

Urochordates have a unique body structure. They possess a tunic, a tough outer covering, which is where the alternate name "Tunicata" comes from. Inside the tunic, there is a body cavity filled with water, and two siphons, the buccal (or incurrent) siphon and the atrial (or excurrent) siphon. The buccal siphon is used to draw in water, which is then filtered for food particles. The filtered water is then expelled through the atrial siphon.

Classification

Urochordata is divided into three classes: Ascidiacea (sea squirts), Thaliacea (salps), and Larvacea (larvaceans). Each class is distinguished by specific characteristics and life cycle stages.

Ascidiacea

Ascidians, or sea squirts, are sessile animals that attach themselves to substrates. They are the most studied class of Urochordata due to their abundance and diversity.

Thaliacea

Thaliaceans, or salps, are free-swimming animals. They are known for their ability to form long chains of individuals.

Larvacea

Larvaceans, unlike the other two classes, retain their notochord and tail throughout their life. They are known for creating complex mucus structures for feeding.

Related Terms

• Chordata: The phylum to which Urochordata belongs.
• Notochord: A defining characteristic of all chordates.
• Ascidians: A class of Urochordata also known as sea squirts.
• Salps: A class of Urochordata also known as Thaliacea.
• Larvaceans: A class of Urochordata that retains its notochord and tail throughout its life.

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