Didemnidae
Didemnidae is a family of colonial tunicates, commonly known as compound ascidians or sea squirts. They are found in all oceans, from the tropics to the polar regions, and are especially abundant in shallow, tropical waters. These small, filter-feeding animals are characterized by their distinctive, often brightly colored, colonial growth forms.
Characteristics
Didemnid colonies are typically composed of numerous individual zooids, each with a distinct body plan. The zooids are usually small, measuring only a few millimeters in length, and are connected to each other by a common tunic, a tough, gelatinous covering that protects the colony. Each zooid has a siphonal opening for inhaling water and a second siphonal opening for exhaling water. The intake of water brings food and oxygen to the zooid, while the exhalation of water removes waste.
The colonies can exhibit a wide range of shapes and sizes. Some species grow as flat sheets or crusts, while others form branching, tree-like structures or even spherical masses. The colonies can vary in color from white or gray to bright yellow, orange, red, or even purple. This colorful variation is often due to the presence of pigments in the tunic.
Environments
Didemnid ascidians are found in a variety of marine habitats, including:
- Intertidal zones
- Subtidal reefs
- Seagrass beds
- Mangrove forests
- Deep-sea environments
They are often found growing on hard substrates such as rocks, coral, or seaweeds. They can also be found on soft substrates such as sand or mud, where they may attach to seagrass or other marine organisms.
Ecology
Didemnid ascidians are important members of marine ecosystems. As filter feeders, they play a vital role in water clarity and nutrient cycling. They also serve as a food source for a variety of marine animals, including fish, crabs, and sea turtles.
Some species of didemnids have been found to contain toxins that can deter predators or even kill other marine organisms. This is due to the presence of symbiotic bacteria that live within the tissues of the ascidians. These bacteria produce a variety of chemical compounds that can be harmful to other organisms.