Bendelormer

Bendelormer, or segmented worms, are a diverse phylum of animals (Annelida) that includes marine polychaetes, freshwater and terrestrial oligochaetes such as earthworms, and leeches. They are characterized by a body divided into repeating segments (metamerism), a true coelom, and a closed circulatory system in most groups. The segments often bear repeated structures such as nerves, excretory organs, and bristles or parapodia in some species.

Anatomy and physiology: the body typically has a distinct head region, a segmented trunk, and a posterior end. Each segment can house components of the nervous, excretory, and reproductive systems. Most bendelormer possess a complete digestive tract and a ventral nerve cord with segmental ganglia. In Clitellata, which include earthworms and leeches, a thickened clitellum forms a mucous cocoon used during reproduction.

Reproduction and development: reproduction is primarily sexual, with many species being hermaphroditic and capable of cross-fertilization. Some bendelormer can reproduce asexually by fragmentation or budding in particular life stages. Development ranges from direct to larval stages in marine forms, depending on the species.

Ecology and significance: bendelormer inhabit marine, freshwater, and terrestrial environments and play key roles in soil formation, nutrient cycling, and sediment structure. They are important for agriculture through vermiculture and serve as model organisms in studies of anatomy, development, and neurobiology. Some species, however, can be invasive and affect native ecosystems.

Examples include the earthworms Lumbricus terrestris and Eisenia fetida, marine polychaetes such as Hediste (Nereis) and other polychaetes, and leeches in the family Hirudidae.