aschelminths

aschelminths (ăsk-hĕlmĭn`thz), large assemblage of loosely related, wormlike organisms of extremely varied structure and habits. Formerly considered an animal phylum, these organisms are now more commonly referred to as pseudocoelomates and are divided in to a number of different phyla, including Nematoda, Gastrotricha, and Rotifera. All are covered by a noncellular coat, or cuticle, and have a pseudocoelom, i.e., a fluid-filled cavity separating the body wall from the gut but lacking a peritoneal lining. In many species the digestive, excretory, and reproductive systems join in a cloaca, or discharge chamber, near the posterior end. Many aschelminths also show cell constancy, a condition in which each organ of the adult contains the precise number of cells characteristic of the species.