An order of Pogonophora, a group of elongate, tentaculated, tube-dwelling, sedentary, nonparasitic marine worms lacking a digestive system. In this order the “coelomic” space in the anterior tentacular region is horseshoe-shaped, and the excretory (osmoregulatory) portion of its ducts come close together medially near the median, adneural blood vessel. The spermatophores are generally broad and leaf-shaped. The tube is often rigid anteriorly. The species in this order are usually large (0.04–0.12 in. or 1–3 mm in diameter) and multitentaculate.