SPOONWORM

also called Echiurid, any member of the primarily marine invertebrate phylum Echiura, also known as Echiuroidea, or Echiurida. Spoonworms are sausage-shaped organisms with a flattened extension of the head that is curved along its lateral edges and sometimes shaped like a scoop or spoon to form a nonretractable anterior proboscis. Adult spoonworms vary from a few to 600 millimetres (2 feet) in length. In Urechis the proboscis is only a fraction of the length of the trunk; however, in Ikeda the proboscis may exceed 10 times the trunk length. Apart from a few brackish-water species, spoonworms are marine and occur in seabeds throughout the world. Although some species inhabit rock crevices, most live in burrows in the mud. A flow of water is maintained through the burrow by peristaltic contractions of the body. Some respiration probably takes place across the body wall, but the hind gut is often utilized as a respiratory organ by drawing water through the anus.