Ctenophora

Comb jellies live in the sea.

They are made of soft jelly. They have eight rows of tiny hairs. These hairs look like little combs.

The combs help them swim. Most of them hunt for food. Some use sticky parts to catch prey. They can be very small or quite large. It is fun to see them move!

Comb jellies live in oceans all over the world.

They are soft animals made mostly of jelly. Their bodies have two thin layers of cells. A thick middle layer called mesoglea sits between them.

Most comb jellies are hunters. They eat tiny things like larvae or small shrimp. Some use colloblasts to catch food. These are sticky cells that help prey cling to them.

Comb jellies are special because of how they move. They have eight rows of tiny hairs called ctenes. These hairs act like little combs. When the hairs beat, the animal swims.

This movement can even make rainbow colors. They do not have a brain. Instead, they have a nerve net. This is a web of nerves under their skin. They also have a special organ to help them balance. This organ has a tiny stone inside. It helps the jelly know which way is up.

Comb jellies are fascinating marine animals found in oceans worldwide.

They belong to a group called Ctenophora, which means "comb-bearing" in Greek. These animals are mostly made of a jelly-like material called mesoglea. This jelly sits between two thin layers of cells.

There are 186 different species known to scientists today. Some are tiny, only a few millimeters long. Others can grow much larger. They are the biggest animals that swim using tiny hairs.

Moving through the water is a special way for these jellies. They have eight rows of tiny hairs called ctenes.

These hairs are arranged in a 9 + 3 pattern. This is different from most other swimming hairs. As these combs beat, they push the animal forward. They usually swim toward their mouths to eat. This movement can even create beautiful rainbow colors. The light hits the moving rows in a special way.

Most comb jellies are predators that hunt for food. They use sticky cells called colloblasts to catch prey.

These cells make prey stick to their tentacles. They eat things like tiny larvae or small crustaceans. Once swallowed, the food is turned into a liquid. A system of internal canals then carries this food. Tiny hairs inside the body help move the food around. This helps the animal digest its meal.

Scientists have studied these animals for a very long time. Fossils of comb jellies have been found in ancient rocks.

These fossils date back to the early Cambrian period. That was about 525 million years ago. There is still a big debate about their history. Some scientists think they are one of the oldest animal groups. Others believe sponges might have appeared even earlier. This is a major topic in the study of life.

Even without a brain, comb jellies can sense their world. They have a nerve net instead of a central brain.

This net of nerves sits just under their skin. They also have a special organ at one end. This organ contains a tiny stone called a statolith. The stone helps the animal sense its balance. It tells the jelly which way is up. This helps them stay steady while they swim.

Ctenophores, commonly known as comb jellies, are a phylum of marine invertebrates found in sea waters across the globe.

There are 186 recognized living species, ranging in size from just a few millimeters to much larger specimens. They are unique because they are the largest animals to swim using cilia, which are tiny, hair-like structures. The name Ctenophora comes from the Greek words for "comb-bearing."

This name describes their most striking feature: rows of beating cilia that look like combs.

The anatomy of a ctenophore is built around a thick, jelly-like middle layer called the mesoglea. This layer is sandwiched between two layers of cells called epithelia.

Because they have these two main cell layers, they have traditionally been called diploblastic. However, some scientists classify them as triploblastic because they possess a type of muscle that arises from the middle layer. Their bodies are quite complex, containing more than 80 different types of cells. This is a higher number of cell types than found in sponges or cnidarians.

Locomotion in ctenophores is achieved through eight distinct strips called comb rows.

These rows run the length of the body from the oral pole, near the mouth, to the aboral pole. Each row holds many "ctenes," or comb plates, which consist of thousands of long cilia. These cilia are arranged in a special 9 + 3 pattern, which is different from the 9 + 2 pattern seen in most other organisms. As these cilia beat, they propel the animal through the water. Most species swim toward their mouths to facilitate feeding.

Most ctenophores are active predators that hunt a variety of prey. They often use specialized cells called colloblasts to capture food. These cells are sticky and allow the animal to adhere to prey like microscopic larvae or small crustaceans.

Once prey is caught, it is swallowed and moved into the pharynx, or throat. In the pharynx, enzymes and muscular contractions turn the prey into a liquid slurry. This slurry is then moved through an internal system of canals by beating cilia. Nutritive cells within these canals digest the food and store nutrients in compartments called vacuoles.

Ctenophores exhibit a wide variety of body forms depending on their species. For example, cydippids are egg-shaped and possess a pair of retractable tentacles for catching prey.

In contrast, beroids have large mouths and often prey on other ctenophores. There are also platyctenids, which are flat and generally lack combs. While many species have rotational symmetry, meaning they look the same when rotated, they do not have perfect mirror symmetry. This is because only two of their internal canals end in anal pores.

Despite their soft bodies, the history of ctenophores reaches back millions of years. Fossils of animals thought to be ctenophores appear in well-preserved fossil beds called Lagerstätten. These fossils date back to the early Cambrian period, roughly 525 million years ago.

There is a major scientific debate regarding their place on the tree of life. Some biologists argue they are the second-earliest branching animal lineage, following sponges. Others, using molecular phylogenetics, suggest the "Ctenophora sister" hypothesis, meaning they branched off even before sponges. This remains a significant taxonomic dispute in biology.

Even without a central brain, ctenophores can sense their environment through a subepidermal nerve net. This network of nerves forms a ring around the mouth and is very dense near the sensory organs.

The most important sensory structure is the aboral organ located at the opposite end of the mouth. This organ contains a statocyst, which is a balance sensor. Inside the statocyst is a tiny grain of calcium carbonate called a statolith. As the statolith moves, it hits bundles of cilia called balancers, telling the animal its orientation in the water.