Very little is known of the biology of this species, but it appears to have an annual cycle, with the entire life cycle occurring within one year (4).

This rare, small worm is ribbon-like in appearance, and has three eyes on its head. The body comprises of 26 or 27 segments, each of which bear bristles known as chaetae (1). The name of this group of worms, polychaetes, means 'many bristles'.

 A small, ribbon-like species, less than 8 mm long with three eyes on its head. It has 26 or 27 segments that bear chitinous bristles.Almost nothing is known of its biology.

Belgian Exclusive Economic Zone, European waters (ERMS scope), Greek Exclusive Economic Zone, United Kingdom Exclusive Economic Zone, Wimereux

This worm was discovered in Eight Acre Pond in Lymington, South Hampshire, in 1984. A large population was still present at this site in 1985 and the species remained in 1990. However, despite repeated surveys for this worm it has not been found since in this pond (3). In 1994 it was discovered nearby in Dorset, at Small Mouth Spit (Portland Harbour), and East Fleet Sandbank, but in very low numbers in both places (3). Outside of Great Britain it has been found in the Mediterranean region (4), the Adriatic, around Madeira and the eastern Atlantic coasts (3).

Depth range based on 5 specimens in 1 taxon.

Environmental ranges
  Depth range (m): 51 - 90

Graphical representation

Depth range (m): 51 - 90
 
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 Found in gravely, sandy and muddy substrata in water only slightly less saline than seawater.

Inhabits muddy, shingle or sandy sediments in water of a salinity that is only slightly less than that of seawater (4).

Classified as 'Insufficiently Known' but 'Possibly Endangered' in the British Red Data Book. Fully protected under Schedule 5 of the Wildlife and Countryside Act 1981 (2) and a UK Biodiversity Action Plan priority species (3).

The loss of this species at Eight Acre Pond may have been the result of changes in salinity or unsuitable drainage (3). As this little-known worm has such a restricted range and occurs in small numbers, it is particularly vulnerable to extinction in Great Britain. Habitat modification or pollution could have devastating effects on this mysterious species (4).

The lagoon sandworm is included in English Nature's Species Recovery Programme; it is also a priority species under the UK Biodiversity Action Plan (UK BAP), and as such has a Species Action Plan. This Action Plan aims to maintain and enhance current populations, and where possible, restore lost populations (3). The species was added to Schedule 5 of the Wildlife and Countryside Act in 1988, and is now afforded full protection (4).