tunicate

Introduction
General features
- Size range and diversity of structure
- Distribution and abundance
- Importance
Natural history
- Reproduction and life cycle
- Locomotion
- Food and feeding
- Associations
Form and function
- General features
- External features
- Internal features
  - Skeleton, tissues, and muscles
  - Nervous system and organs of sensation
  - Digestion, nutrition, and excretion
  - Respiration
  - Water/vascular system
  - Hormones
  - Features of defense and aggression
Evolution and paleontology
Classification
- Annotated classification
- Critical appraisal

References & Edit History Quick Facts & Related Topics

Images

Bright blue sea squirt Rhopalaea crassa with yellow-edged openings grows on a coral reef among various corals in the Philippines.

Underwater view of a glowing chain of tunicates with a scuba diver and boat visible near the water's surface in the background.

At a Glance

tunicate summary

Quizzes

Sea otter (Enhydra lutris), also called great sea otter, rare, completely marine otter of the northern Pacific, usually found in kelp beds. Floats on back. Looks like sea otter laughing. saltwater otters

Animal Group Names

Deadliest Animals Quiz

Match the Baby Animal to Its Mama Quiz

The bearded vulture (Gypaetus barbatus) is seen in Switzerland on December 2024

Animal Factoids

Related Questions

How are pyrosomes different from salps and dolioloids?
How are tunicates important in marine food chains?
How can tunicates become fouling organisms on ships?
How do adult appendicularians resemble tunicate larvae?
How do appendicularians differ from most adult tunicates?
How do ascidians differ from appendicularians?
How do dolioloids reproduce through alternating generations?
How do sexual and asexual reproduction differ in tunicates?
How do some tunicates protect embryos before larvae develop?
How do tunicates differ from cephalochordates?
How does budding allow tunicate colonies to reproduce?
How large can tunicate colonies grow?
How long does the tunicate larval stage last?
How many tunicate species are known?
What are the three main classes of tunicates?
What happens to the nerve cord during tunicate metamorphosis?
What is the tough outer tunic of a tunicate made of?
What role do gill slits play in tunicate feeding?
Where are free-swimming tunicates found in the ocean?
Where are tunicate eggs fertilized?
Where do sessile tunicates live in the ocean?
Which features do tunicate larvae share with other chordates?
Why are sea squirts also called ascidians?
Why are thaliaceans adapted for life in open water?
Why do adult sea squirts lose their tails and notochords?
Why do appendicularians retain a notochord and tail as adults?
Why do soft-bodied tunicates leave few fossils?
Why do tunicates grow on ship hulls and wharf piles?
Why is cellulose in tunicate tunics unusual among animals?
What are five facts about bald eagles?
When did the bald eagle become the national bird of the U.S.?
What do koalas eat?
How many types of deer are there?
How fast do snakes grow?
What is molting in snakes?
What are the physical characteristics of a red panda?
Where can red pandas be found in the wild?
What are the main threats to red pandas?
How do red pandas reproduce?

Science Insects & Other Invertebrates

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External Websites

University of Washington - Departments Web Server - What's a Tunicate?
The Royal Society Publishing - Open Biology - Tunicates: exploring the sea shores and roaming the open ocean.
UNESCO - Encyclopedia Life Support Systems - Tunicata and Cephalochordata
Earth Life - Tunicates: Miraculous Sea Squirts Named After Their "Tunics"
BMC - BMC Biology - A phylogenomic framework and timescale for comparative studies of tunicates
National Center for Biotechnology Information - Early Development in Tunicates
Smithsonian Ocean - Tunicatesï¿½Not So Spineless Invertebrates
Maine.gov - Department of Marine Resources - Tunicates aka Sea Squirts

tunicate

chordate subphylum

Also known as: Tunicata, Urochordata, urochordate

Written by

Michael T. Ghiselin

Senior Research Fellow, California Academy of Sciences, San Francisco. Author of The Triumph of the Darwinian Method.

Michael T. Ghiselin

Fact-checked by

Britannica Editors

Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....

Britannica Editors

Last updated

Nov. 2, 2026 •History

tunicate, any member of the subphylum Tunicata (Urochordata) of the phylum Chordata. Small marine animals, they are found in great numbers throughout the seas of the world. Adult members are commonly embedded in a tough secreted tunic containing cellulose (a glucose polysaccharide not normally found in animals). The less modified forms are benthic (bottom-dwelling and sessile), while the more advanced forms are pelagic (floating and swimming in open water). A characteristic tadpole larva develops in...

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