Segmented worms are a topic within invertebrate zoology encompassing organisms in the phylum Annelida, characterized by a metameric body plan in which serially repeated segments (metameres) contain reiterated organ systems, often separated internally by septa. This segmentation underlies specialized locomotion via segmentally arranged circular and longitudinal muscles acting against a fluid-filled coelom as a hydrostatic skeleton. Annelids exhibit a closed vascular system, well-developed nervous system with a ventral nerve cord and segmental ganglia, and diverse feeding and reproductive strategies. Research on segmented worms informs developmental patterning, regeneration, soil ecology, and comparative morphology of body plan evolution among bilaterian animals.
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