Symbion

Tiny animals live on lobsters.

They stay near the lobster mouth. They eat the lobster's leftover food. These little ones are very small. They look like tiny sacs. They have three different life stages. Some are big and eat food. Some are males. Some are females. They live on cold-water lobsters. They grow and change as they get older. It is a very busy life for such small things!

Symbion is a tiny animal that lives on lobsters.

They live in cold water. They stay near the mouth of the lobster. These animals eat the leftover food from the lobster. They are so unique that scientists gave them their own group. This group is called Cycliophora.

These animals have three life stages. The first stage is for feeding. These individuals are the largest. They have a sac-like body. They use a small stalk to glue themselves to the lobster. They have a mouth to eat food.

The second stage is the sexual stage. This stage has males and females. Males do not have a mouth or a stomach. They do not eat. They make tiny dwarf males inside their bodies. These dwarf males are very small. They have only 47 cells when they are grown.

The third stage is the female stage. Females have a stomach. They carry one egg inside them. The egg takes nutrients from the mother. When the female is born, she is an empty shell. She must find a new spot on the lobster. She will then grow into a large feeding adult.

Symbion is a tiny animal found in cold water. These animals live on the mouthparts of lobsters. They are very small, measuring less than 0.5 mm wide. They have a special way of living with their hosts. This is called commensalism, which means they eat leftover food from the lobster. Because they are so unique, scientists gave them their own group. This group is called the phylum Cycliophora, or "wheel wearers."

The life of a Symbion has three main stages. The first stage is the asexual feeding stage. These are the largest individuals, measuring 347 μm long. They have a sac-like body with a mouth and an anus. A small stalk with an adhesive disc glues them to the lobster. They use this stage to eat and make copies of themselves. During autumn, a new individual grows inside the parent body. This helps the species survive when a lobster sheds its shell.

In early winter, the animals begin the sexual stage. This stage includes both males and females. The males are small, about 84 μm long. They have no mouth or digestive system, so they do not eat. A male will crawl away and glue himself to an asexual adult. Inside the male, two tiny dwarf males grow. These dwarf males are 100 times smaller than the adult. They only have 47 cells when they are fully grown.

Scientists discovered these animals in 1995. Reinhardt Kristensen and Peter Funch found Symbion pandora. They found them on the mouthparts of the Norway lobster. Other species live on the American lobster and the European lobster. This was a big moment for science. It was the first new phylum of multi-celled organisms found since 1983. Scientists use genetic analysis to study how they are related to other life.

You can think of Symbion like a tiny passenger on a big ship. The lobster is the ship, and the Symbion is the passenger. The passenger does not hurt the ship, but eats the crumbs left behind. The life cycle is a complex way to make many offspring. A female carries one egg inside her body. The growing embryo takes nutrients from the mother. This leaves the mother as an empty husk when she is born. The new female must find a new spot on the lobster to grow.

Symbion is a unique genus of tiny aquatic animals. These creatures are less than 0.5 mm wide. They live in cold waters attached to lobster mouthparts. They practice a lifestyle called commensalism. This means they live on a host without harming it. They simply eat the leftovers from the lobster's meals. Because they are so biologically distinct, scientists placed them in their own phylum. This group is named Cycliophora, which means "wheel wearers."

The life cycle of a Symbion is very complex. This strategy helps them survive when a lobster sheds its shell. They move through three distinct biological stages. The first is the asexual feeding stage. In this stage, the animal is neither male nor female. These individuals are the largest members of the species. For example, Symbion pandora measures 347 μm in length and 113 μm in width. They have a sac-like body with no coelom, which is a body cavity. A stalk with an adhesive disc holds them to the lobster. At the front end, they have a ciliated funnel for a mouth and an anus for waste.

The second stage is the sexual stage, which includes males and females. During autumn, the asexual individuals make copies of themselves. A new individual grows inside the parent body one at a time. In early winter, these asexual animals begin producing males. The males are much smaller, measuring about 84 μm long and 42 μm wide. Interestingly, males have no mouth or digestive system. They do not eat during this stage. Instead, they focus entirely on reproduction. A male will crawl away from his parent to find another asexual individual. He glues himself to that individual to begin the next step.

Inside the male, a fascinating process creates dwarf males. These tiny males are about 100 times smaller than the asexual individual. They start with about 200 cells, but this number drops to 47 at maturity. Most of these cells form a nervous system of 34 cells. Three cells become sensory cells to feel the surroundings. Eight cells become mucous glands to help them move. The final two cells form the testes to produce sperm. To fit two males inside a parent, most cells lose their nucleus and shrink. This adaptation allows two mature males to reside in one hollow pouch. Having two males increases the chance of fertilizing a female.

By late winter, the colony begins producing females. Each female carries a single egg inside her body. When she is ready to be born, one of the dwarf males fertilizes her. The fertilized female must find a place on the lobster's whiskers. She attaches herself there to begin her life. As the embryo develops, it extracts nutrients from the mother. This process leaves the mother as an empty husk by the time she is born. If the new individual successfully finds a host, she will grow a mouth and stomach. She will eventually morph into the large, asexual feeding form to start the cycle again.

History shows that Symbion was a major discovery for science. Reinhardt Kristensen and Peter Funch discovered Symbion pandora in 1995. They found them on the mouthparts of the Norway lobster. Since then, related species have been found on American and European lobsters. This discovery was very significant for biologists. Cycliophora was the first new phylum of multicelled organisms found since 1983. This was when the Loricifera phylum was identified. Because they look so different from other animals, they required their own unique classification.

Scientists are still studying the exact place of Symbion in the tree of life. Their phylogenetic position is not yet fully settled. This means researchers are still deciding exactly how they are related to other groups. Currently, genetic analysis places them in a clade called Polyzoa. This group also includes the phyla Ectoprocta and Entoprocta. Studying their DNA helps scientists understand how these tiny "wheel wearers" fit into the wider world of marine life.