Nereis

Nereis is a genus of marine bristle worms in the family Nereididae, comprising numerous species of polychaete annelids commonly known as ragworms or sandworms. They occur in oceans worldwide, with many species inhabiting shallow coastal areas, estuaries, and intertidal zones where they burrow in sand or mud or move across substrates.

Morphology and anatomy: Nereis worms have elongated, segmented bodies with numerous bristle-bearing parapodia on each segment. They possess a eversible proboscis equipped with jaws that they use to grasp prey. The head region (prostomium) bears sensory structures, and the body typically shows variability in segment number and pigmentation among species.

Ecology and habitat: Most Nereis species are benthic burrowers in soft substrates, though some are more mobile or free-swimming. They contribute to bioturbation, mixing and aerating sediments, and they function as active predators of small invertebrates. They serve as an important food source for fish, birds, and other marine predators, linking sediment ecosystems to higher trophic levels.

Life cycle and reproduction: Reproduction is generally sexual and often dioecious. Several species exhibit epitoky, where a portion of the worm becomes a reproductive swell that migrates to the water column to release gametes in synchronized spawning. Larval development typically includes trochophore and subsequent larval stages before settling as juvenile worms.

Human relevance: Nereis species are widely harvested as fishing bait and are used in ecotoxicology and environmental monitoring due to their sensitivity to sediment quality and pollutants. Notable species include Nereis virens (common ragworm) and Nereis diversicolor (sandworm).