A rarer order of the class Anopla in the phylum Rhynchocoela, characterized by an unarmed proboscis, a thin gelatinous dermis, and either a two-layered (outer circular and inner longitudinal strata) or three-layered (outer circular, median longitudinal, and inner circular strata) body musculature. Many members (such as Tubulanus = Carinella) show primitive features, such as a peripherally located nervous system and the absence of ocelli, ciliated grooves, and intestinal diverticula. Cerebral organs, if present, are generally simple.