Nemertea
Nemertea, commonly known as ribbon worms or proboscis worms, are a phylum of invertebrate animals that are exclusively marine. These worms are characterized by their elongated, flattened bodies and a unique proboscis, a tubular structure that can be everted to capture prey. They are found in a variety of marine habitats, from shallow intertidal zones to deep-sea environments. There are over 1,300 described species of nemerteans, making them one of the most diverse phyla of marine invertebrates.
Characteristics
Nemerteans possess a number of distinctive characteristics that set them apart from other marine invertebrates. These include:
- Proboscis: A muscular, eversible tube located in the dorsal portion of the body, used for capturing prey. The proboscis is often armed with sharp stylet that inject toxins.
- Closed circulatory system: Blood is contained within vessels and is pumped by a heart.
- Complete digestive system: Nemerteans have a mouth, pharynx, intestine, and anus.
- Bilateral symmetry: The body is divided into two symmetrical halves.
- Variety of sizes: Nemerteans range in size from a few millimeters to several meters in length.
Environments
Nemerteans are found in a wide variety of marine environments around the world, including:
- Intertidal zones: These are areas that are alternately exposed to air and water. Nemerteans in these zones are often found under rocks, in seaweed, or in sand.
- Subtidal zones: These are areas that are constantly submerged in water. Nemerteans in these zones are often found on seafloor sediments, in coral reefs, or on seaweeds.
- Deep-sea environments: These are areas that are more than 200 meters below the surface. Nemerteans in these zones are often found in trenches, canyons, and on hydrothermal vents.