Segmented worms, also known as annelids, are a diverse and abundant group of invertebrates belonging to the phylum Annelida. They are characterized by their unique body structure consisting of numerous segments or rings along their length. Each segment is separated by a distinct partition called a septum, hence the name "segmented worms."
These animals can be found in various habitats ranging from terrestrial to aquatic ecosystems, including soil, freshwaters, and marine environments. The most commonly known and observed members of this group include earthworms, leeches, and bristleworms.
Segmented worms exhibit a wide range of sizes, with some species being just a few millimeters long, while others can grow up to several meters in length. Their elongated bodies are bilaterally symmetrical, meaning they have identical left and right halves. The body is typically cylindrical and can be flexible, allowing them to move and burrow through the substrate efficiently.
Segmented worms are known for their well-developed coelom, a fluid-filled cavity that surrounds and protects their internal organs. This coelomic space serves various functions, such as facilitating movement and providing hydrostatic support to the body. Another significant characteristic of segmented worms is the presence of setae, bristle-like appendages protruding from the body segments. These setae are used for locomotion, anchoring, and sensing the environment.
Segmented worms exhibit a variety of feeding habits. Some are detritivores, feeding on decaying organic matter, while others are predators, scavengers, or filter feeders. The digestive system in segmented worms generally comprises a muscular pharynx, esophagus, crop, gizzard, and an intestine that runs the length of the body.
Reproduction in segmented worms can
