Polynoidae

Polynoidae is a large family of marine polychaete worms, commonly known as scale worms. They belong to the order Phyllodocida within the class Polychaeta and are distinguished by a dorsoventrally flattened body with a row of elytra, or scales, on most segments. The elytra are often shed and regrown as the animal grows, giving many species a glossy, segmented appearance. Parapodia are well developed, bearing chaetae on both notopodia and neuropodia, and the prostomium typically bears paired antennae and palps. Body coloration and elytral patterns are highly variable among species.

Distribution and habitat are cosmopolitan. Polynoidae occur from shallow coastal waters to the deep sea in a wide range of substrates, including rocky substrates, soft sediments, algal beds, and coral reefs. A substantial portion of the family is composed of commensal or epibiotic species that attach to or live on other invertebrates, such as echinoderms, cnidarians, or sponges, while others are free-living predators or scavengers.

Reproduction is sexual, with many species producing free-swimming larvae typical of polychaetes; some taxa show direct development. The family is taxonomically diverse and contains numerous genera. Systematic work integrates morphological and molecular data, and classifications continue to be revised as new information becomes available. Key diagnostic characters include elytral number and arrangement, chaetal morphology, and branchial structures.

Ecologically, Polynoidae contribute to benthic biodiversity and community dynamics and are studied as indicators of habitat health and as models for host–symbiont interactions.