echiuroids

Echiuroids, commonly known as spoon worms, are a group of marine annelids that have historically been treated as a separate phylum (Echiura) but are now generally classified within Annelida as an unsegmented lineage. They are distinguished by a prominent, extensible proboscis used to collect food from the surrounding sediment. The main body is elongated and smooth, lacking the bristles (setae) and parapodia typical of many other annelids. The proboscis is often highly mobile and can be projected to gather organic particles, which are transported to the mouth for ingestion. The digestive tract usually runs the length of the trunk and ends at the anus.

Echiuroids inhabit soft marine sediments worldwide, from shallow coastal zones to deep oceans. They are typically burrow-dwellers and may construct burrows that extend into the sediment or reside in mucus-lined spaces. Their feeding is primarily deposit-based, as they ingest sediment and extract organic matter, microorganisms, and detritus. They play a significant ecological role as bioturbators, helping to mix, aerate, and influence the chemistry of the sediment.

Reproduction is usually sexual, with separate sexes in many species, and most produce free-swimming larvae that settle to become adults. Life histories can be diverse, and some species exhibit notable variations in reproductive strategy. Echiuroids are less studied than many other annelids due to their secretive lifestyles, but they are ecologically important in marine benthic ecosystems and can serve as indicators of sediment health in some regions.