Echiuroidea
Echiuroidea, commonly known as spoon worms or echiurans, are a group of marine worms belonging to the phylum Annelida. They are characterized by their distinctive spoon-shaped proboscis, which they use for feeding and burrowing. Echiurans are found in a variety of marine habitats, from shallow coastal waters to deep-sea trenches, often inhabiting burrows in soft sediments. They play an important role in marine ecosystems, contributing to sediment turnover and nutrient cycling.
Characteristics
Echiurans are typically unsegmented worms, with a distinct proboscis that can be extended and retracted. They have a closed circulatory system and lack specialized respiratory organs, relying on diffusion for gas exchange. Echiurans are mostly deposit feeders, using their proboscis to collect organic matter from the sediment. Some species have a pair of long, contractile setae (bristles) located near the anus, which they use for anchoring themselves in their burrows.
Environments
Echiurans are found in a wide range of marine environments, including:
- Intertidal zones
- Continental shelves
- Deep-sea trenches
- Coral reefs
- Seagrass meadows
They are typically found in soft sediments, such as mud, sand, or silt, where they burrow and feed.
Reproduction
Echiurans are dioecious, meaning they have separate sexes. They reproduce sexually, with females releasing eggs into the water, where they are fertilized by sperm from males. The resulting larvae undergo a series of developmental stages before metamorphosing into adults.
Classification
Echiuroidea is a class within the phylum Annelida. The class is divided into two orders:
- Echiurida
- Bonelliidae
There are over 150 known species of echiurans.
References