Relationships within the phylum are still somewhat unclear, but two classes are recognised. The five marine species of nematomorph are contained in Nectonematoida.Pechenik, 'Biology of the Invertebrates, 2010, pg 457. This order is monotypic containing the genus Nectonema Verrill, 1879: adults are planktonic and the larvae parasitise decapod crustaceans, especially crabs. They are characterized by a double row of natotory setae along each side of the body, dorsal and ventral longitudinal epidermal cords, a spacious and fluid-filled blastocoelom and singular gonads.
relationships within the phylum are still somewhat unclear but two classes are recognised the five marine species of nematomorph are contained in nectonematoidapechenik 'biology of the invertebrates 2010 pg 457 this order is monotypic containing the genus nectonema verrill 1879 adults are planktonic and the larvae parasitise decapod crustaceans especially crabs they are characterized by a double row of natotory setae along each side of the body dorsal and ventral longitudinal epidermal cords a spacious and fluid-filled blastocoelom and singular gonads