Tunicate

Some sea animals wear a coat.

This coat is like a small tunic. It can be soft or tough.

These animals live in the ocean. They eat by pulling in water. They use two small tubes to do this. One tube lets water in. The other tube lets water out.

Some live all alone. Others live in big groups. These groups are called colonies.

Some tunicates stay in one place. They stick to rocks or shells. Others can swim in the sea. They move through the water.

They can look like many things. Some look like grapes or seeds. They are very special sea life.

Tunicates are sea animals that live in the ocean.

Most live in shallow water. There are about 3,000 different species.

These animals wear a special outer covering. We call this a tunic. It acts like an exoskeleton, which is a hard outer shell. This tunic can be thin and clear. Other types are thick and tough.

Tunicates eat by filtering water. They have two tube-like openings called siphons. One siphon draws water in. The other siphon lets water out. Inside, they use a sticky net to catch food.

Some tunicates live all alone. They stay in one spot on rocks or shells. These are called sessile animals. Others live in large groups called colonies.

Each tiny part of a colony is a zooid.

Some tunicates can swim in the open sea. These are called pelagic animals. They use jet propulsion to move. This means they push water to move forward. Tunicates are close relatives to humans. As babies, they look like tiny tadpoles.

Tunicates are fascinating marine invertebrates that live in the world's oceans. Most of these creatures live in shallow waters. There are about 3,000 different species of tunicates. They are part of a larger group called Chordata. This group includes all animals with a dorsal nerve cord. Even though many adults look very simple, they are closely related to vertebrates.

This connection is easy to see in their mobile larval stage. As babies, they look like tiny tadpoles. They have a notochord and a tail just like other chordates.

Most tunicates are filter feeders that live in a sac-like body.

They use two tube-like openings called siphons to eat. The incurrent siphon draws water into the body. Inside, a muscular tube called a pharynx uses a sticky mucous net to catch food. This net is made by a part called the endostyle. After the food is caught, the water is pushed out through the excurrent siphon.

This way of eating helps them stay healthy while staying in one place.

Scientists have been studying these animals for a long time.

The name "tunicate" was first used by James Lee in 1760. He named them after the tunic, which is their outer covering. In 1816, Jean-Baptiste Lamarck established the group Tunicata. Later, in 1881, Francis Maitland Balfour used the name Urochordata. He wanted to show how they are related to other chordates. Today, most scientists prefer the original name, Tunicata.

There are many different types of tunicates to discover.

The largest group is called the Ascidiacea. Many of these are sessile, which means they stay attached to rocks or shells. Some live in colonies where many tiny units, called zooids, live together.

Other groups, like Thaliacea, swim in the open sea. Pyrosomes are colonial tunicates that can actually glow in the dark. One very large species is the sea tulip, which can grow over 10 centimeters tall.

Learning about tunicates helps us see how life is connected.

Even though they look different from us, we share a common history. Their outer tunic is a unique exoskeleton made of proteins and carbohydrates. This covering can be thin and clear or thick and tough. Some species, like sea squirts, can contract their bodies to spray water. This behavior is how they get their common name. They remind us that even the simplest looking animals have amazing stories.

Tunicates are a diverse group of marine invertebrates belonging to the subphylum Tunicata.

They are members of the phylum Chordata, which includes all animals possessing a notochord and a dorsal nerve cord. This phylum also contains all vertebrates, such as fish, birds, and humans. While many adult tunicates appear quite simple, they share a deep evolutionary connection to vertebrates. This relationship is most visible during their mobile larval stage.

These larvae resemble tadpoles and possess a notochord, a hollow dorsal nerve cord, pharyngeal slits, a post-anal tail, and an endostyle. Tunicates are unique among chordates because they have lost myomeric segmentation, though some doliolids still show muscle band segmentation.

Most tunicates function as marine filter feeders using a specialized sac-like body structure.

Their bodies contain two tubular openings known as siphons. To feed, they draw water into the interior through the incurrent, or inhalant, siphon. Inside the body, a large muscular tube called the pharynx links the buccal opening to the gut. A ciliated groove on the ventral surface of the pharynx, called the endostyle, secretes a mucous net.

This net captures food particles as water passes through. The water then exits the body through the excurrent, or exhalant, siphon. The pharynx walls are perforated by bands of slits called stigmata, which allow water to escape into the atrial cavity.

Scientists classify the roughly 3,051 described species into three main classes. The largest class is Ascidiacea, which contains the majority of tunicate species. Many ascidians are sessile, meaning they are immobile and permanently attached to substrates like rocks, shells, or ship hulls.

Some ascidians live as solitary individuals, while others form colonies of many tiny units called zooids. The second class is Thaliacea, which includes free-swimming, pelagic organisms. This class contains pyrosomes, doliolids, and salps. The third class is Appendicularia, also known as larvaceans. These organisms occupy different ecological niches, from the seabed to the open ocean.

History shows a long period of debate regarding the naming of these animals. The term "tunicate" was coined in 1760 by the nurseryman James Lee. He suggested the name because the animals appear to be "clothed" in a protective outer layer. In 1816, Jean-Baptiste Lamarck formally established the group Tunicata. Later, in 1881, Francis Maitland Balfour introduced the name Urochordata to emphasize their relationship to other chordates.

Although "Urochordata" was widely used for many years, modern scientific consensus favors the original name, Tunicata. This preference is supported by the World Register of Marine Species.

Physical diversity among tunicates is quite vast. Their outer covering, or tunic, serves as an exoskeleton made of proteins and carbohydrates. This tunic can be thin and gelatinous or thick and stiff.

Some species are even bioluminous, such as the colonial pyrosomes found in tropical waters. Tunicates also display a wide variety of shapes; they can resemble seeds, grapes, barrels, or even bottles. One notable example is the stalked sea tulip, Pyura pachydermatina, which can grow to over 10 centimeters in height. Other common names, like "sea squirts," come from the way these animals contract their bodies to expel water when disturbed.

The fossil record for tunicates is relatively sparse because their soft bodies decay quickly after death.

However, some evidence suggests their basic body design was established at least 500 million years ago. The Middle Cambrian fossil Megasiphon thylakos is a well-preserved example of this ancient design. There are also possible traces of tunicates from the Ediacaran period, such as Ausia and Burykhia, which lived in shallow coastal waters over 548 million years ago. In some cases, microscopic structures called spicules have been found in Jurassic rocks, though these are sometimes mistaken for sponge spicules.

Tunicates provide important insights into the evolution of complex life. They belong to a clade called Olfactores, which links them closely to craniates like lampreys and jawed vertebrates. This connection helps scientists understand how the fundamental traits of chordates developed over time. By studying the transition from mobile larvae to sessile adults, researchers gain a better understanding of biological complexity. Their unique method of colonial living and specialized feeding also helps explain how marine ecosystems function.