Bilateria with weakly multicellular epidermal cells, the cilia being devoid of an accessory centriole at the basal body. The bilaterally symmetrical protonephridia provided with more than one terminal cell; terminal and canal cells biciliar, both cilia without accessory centriole and without an inner circle of 8 microvillar rods. Epidermal cells and other somatic cells do not undergo any mitosis.