Phoronid

Small worms live in the sea.

They build tiny tubes for homes. These tubes help keep them safe.

At the top, they have a crown of arms. Tiny hairs on the arms catch food. The food moves into their mouth. This helps the worms eat. They can pull their bodies into their tubes very fast. This hides them from danger. Most of these worms live for one year. They are very small animals.

Do you like the ocean?

Phoronids are small marine animals. People often call them horseshoe worms.

They live in many parts of the ocean. They build tubes to live in. These tubes are made of chitin. Chitin is a tough material. The tubes protect their soft bodies.

Most adult worms are about 2 cm long. At the top, they have a lophophore. This is a crown of tentacles. Tiny hairs called cilia live on the tentacles. These hairs move food toward the mouth. The worms can also use the hairs to push away bad food.

Inside their body, they have a stomach. A blood vessel moves blood through the body. They do not have a heart. Instead, muscles move the blood in waves. Their blood has hemoglobin. This helps them use oxygen in places with very little air.

Young worms start as larvae. They are called actinotrochs. These tiny swimmers eat plankton. After 20 days, they settle on the sea floor. They change their body shape very fast. They grow into adult worms in just 30 minutes.

Phoronids are tiny animals that live in the ocean. Many people call them horseshoe worms because of how they look.

These creatures live in many different seas and oceans. They can be found in the Arctic Ocean, but they do not live in the Antarctic Ocean. Most of them stay between the shore and 400 meters deep. They build upright tubes to stay safe and supported. These tubes are made of chitin, which is a tough material.

Feeding is a very interesting way for these worms to work. At the top of their body, they have a lophophore. This is a crown of tentacles used to catch food. Tiny hairs called cilia grow on the sides of these tentacles. The cilia pull food particles toward the mouth. If the worm finds something it does not want, it can close a lid called an epistome. The cilia can even switch to reverse to push bad food away. The food then travels down to a stomach located in a part called the ampulla.

Scientists have studied these animals for a long time. We do not have any clear body fossils of phoronids from the past. However, we see trace fossils that might have been made by them. These traces come from the Silurian, Devonian, Permian, Jurassic, and Cretaceous periods. The name for the group comes from the genus Phoronis. This name likely comes from a Greek myth about a priestess named Phoronis.

There are many specific details about how a phoronid grows. Most adult worms are about 2 cm long and 1.5 mm wide. Some very large ones can reach 50 cm in length. They live for about one year. When they are young, they are called actinotroch larvae. These tiny swimmers eat plankton in the ocean. After about 20 days, they settle on the seabed. They undergo a huge change in just 30 minutes to become adults.

Even though they are small, their bodies have amazing features. They do not have a heart to pump their blood. Instead, muscles in their blood vessels contract in waves to move it. Their blood contains hemoglobin to help them breathe in low-oxygen water. In one species, the blood carries twice as much oxygen as human blood. They also use special parts called metanephridia to filter their body fluids. This helps them keep their bodies clean and healthy.

Phoronids, often called horseshoe worms, are a phylum of small marine animals. They are defined by a specialized feeding structure called a lophophore. This structure is a crown of tentacles used to capture food from the water. Phoronids are important to marine ecosystems because they live in many oceans. They inhabit areas from the intertidal zone down to depths of about 400 meters. While they are found in the Arctic Ocean, they do not live in the Antarctic Ocean.

The anatomy of a phoronid is built for both feeding and protection. Most adults are roughly 2 cm long and 1.5 mm wide. However, some large species can reach 50 cm in length. They live inside upright tubes made of chitin, a tough organic material. The bottom of their body features a flask-like swelling called an ampulla. This ampulla anchors the animal inside its tube. If a predator approaches, longitudinal muscles allow the phoronid to retract its body very quickly. This rapid movement can reduce the body to only 20 percent of its maximum length.

Feeding and respiration happen through the lophophore at the top of the body. The tentacles are hollow and held upright by internal fluid pressure. Tiny hairs called cilia line the sides of these tentacles. These cilia draw water through the crown and push food particles toward the mouth. The mouth is located just inside the base of the lophophore. To prevent eating bad material, the animal uses a lid called an epistome. This lid can close the mouth entirely. The cilia can also switch to reverse to reject unwanted particles.

Once food enters the mouth, it travels through the gut to the stomach. The stomach is located within the ampulla at the bottom of the body. Solid waste moves up the intestine and exits through the anus. The anus is positioned outside and slightly below the lophophore. To move nutrients, the phoronid uses a specialized circulatory system. It does not have a heart to pump its blood. Instead, the major blood vessels contract in waves to move the blood through the body. This system includes a circular vessel at the lophophore base and various branches throughout the body.

Phoronids have unique adaptations for living in low-oxygen environments. They do not ventilate their trunks with oxygenated water. Instead, they rely on respiration through the lophophore. Their blood contains hemoglobin, which is unusual for animals of such small size. This is an adaptation to anoxic or hypoxic conditions, where oxygen is very low. For example, the blood of Phoronis architecta carries twice as much oxygen per gram of body weight as human blood. To manage waste, two organs called metanephridia filter the body fluid. These organs return useful products to the body and expel soluble wastes through pores near the anus.

The life cycle of a phoronid involves a dramatic transformation. Most species reproduce sexually from spring to autumn. The eggs develop into free-swimming larvae known as actinotrochs. These larvae feed on plankton in the open water.

After about 20 days, an actinotroch settles on the seabed. In just 30 minutes, it undergoes a radical metamorphosis to become an adult. The larval tentacles are replaced by the adult lophophore. The anus moves from the bottom of the body to a position outside the lophophore. This change also shifts the gut from an upright shape to a U-bend.

History and classification provide insight into how these animals relate to others. Phoronids belong to a group called lophophorates, which includes brachiopods and bryozoans. All these animals use a lophophore to feed. For many years, scientists thought lophophorates were closely related to deuterostomes, a group including humans. However, most modern researchers now place phoronids in the protostome super-phylum Lophotrochozoa. While we do not have indisputable body fossils, we find trace fossils from the Silurian and Devonian periods. These traces suggest phoronids have existed in the oceans for a very long time.