Nematomorpha

Nematomorpha (commonly known as horsehair worms) are a phylum of parasitic animals morphologically and ecologically similar to nematodes. ~320 described species of hair worms 1–3mm in diameter, 1m long External cuticle without cilia Longitudinal muscles only (similar to nematodes) Adults free living Non-functional gut No excretory, respiratory or circulatory system Dioecious, internal fertilization eggs laid in gelatinous strings Unusual cleavage Larval form are parasitic in arthropods

Order Nectonematoida: Marine, planktonic, with a double row of natotory setae along each side of the body; with dorsal and ventral longitudinal epidermal cords, blastocoelom spacious and fluid filled; gonads single; larvae parasitize decapod crustaceans

Order Gordioidea: Freshwater and semiterrestrial; lack lateral rows of setae; with a single, ventral epidermal cord; blastocoelum filled with mesenchyme in young animals but becomes spacious in older individuals; gonads grasshoppers and crickets.