Spoonworm

spoonworm, also called echiurid, any member of the invertebrate phylum Echiura, also known as Echiuroidea, or Echiurida. Nearly all spoonworms are exclusively marine. They 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, highly muscular, anterior proboscis. The proboscis is used for food collection. 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. About 150 species have been described.

Spoonworms occur in seabeds throughout the world. Although some species inhabit rock crevices, most live in burrows in the mud. A few species even occur in brackish water. A flow of water is maintained through the burrow by peristaltic contractions of the body wall muscles. Some respiration probably takes place across the body wall, but the hind gut is often utilized as a respiratory organ by pumping water in and out through the anus.