echiuran

Echiurans are a small phylum of marine invertebrates, comprising only about 230 described species. They are commonly known as spoon worms due to the distinctive, flattened, scoop-like proboscis that most species possess. This proboscis is used for feeding, extending from the mouth to sweep up organic matter from the seafloor or from within sediment. Echiurans have a segmented larval stage, but this segmentation is lost in adulthood, resulting in a simple, unsegmented body.

The body of an echiuran is typically divided into a main trunk and the proboscis. The trunk is muscular and often contains a coelom, a fluid-filled body cavity. They lack a circulatory system and respiratory organs, instead relying on diffusion for gas exchange. Reproduction is sexual, with separate sexes in most species, though some are hermaphroditic. Fertilization is external, and larvae develop through a planktonic stage before settling to the seabed.

Echiurans are found in all the world's oceans, from shallow intertidal zones to the deep sea. They inhabit a variety of substrates, including sand, mud, and gravel, and many species burrow into the sediment. Some echiurans also live commensally within the burrows of other animals. Their diet consists primarily of detritus, which they gather using their proboscis. Despite their relatively simple anatomy, echiurans are a unique and ecologically significant group of marine organisms.