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Species
Lagoon sea slug
Tenellia adspersa
This tiny, rare sea slug is, at its largest, 8mm long, and often reaches only half that size. Much more attractive than their name suggests (and than land slugs), lagoon sea slugs have mobile, finger-like structures around the edges of their bodies. They are pale brown, and marked with small dark spots.
Lagoon sea slugs live in shallow water, and can be found on the shore between the tides. They like the sheltered conditions of bays and harbours. Lagoon sea slugs prefer landscapes of pebbles, larger stones and small rocks and can also be found in seaweed and seagrass beds. They do not eat plants, however, and are actually predators that feed on hydroids (anemone or jellyfish-like creatures that live on the seabed).
Lagoon sea slugs can be found in different areas, between which the saltiness of the water varies considerably. They have been found upstream in estuaries in virtually freshwater conditions and, at the other extreme, in highly salty coastal lagoons.
The sea slugs’ common name comes from their association with these lagoons, and it is the threats to the lagoons from pollution, in-filling and coastal defences that present the most serious known threat to the populations of the sea slugs.
Brief description of European distribution
The few British records of the lagoon sea slug have been on the southern and western coasts of England, but the full European distribution extends to the eastern and western North Atlantic, and the Baltic and Mediterranean Seas.
Conservation status / need
UK BAP Priority species
Protected under Schedule 5 of the Wildlife and Countryside Act 1981
Nationally rare marine animal
Listed as Insufficiently known but at least Rare in the British Red Data Book
The coastal lagoons in which the sea slugs can be found are a UKBAP priority habitat and are listed in Annex I of the Habitats Directive
Further information sources
Lagoon sea slug - Tenellia adspersa
(MarLIN)
Tenellia adspersa (Encyclopedia of Marine Life of Britain and Ireland)
Lagoon sea slug (Tenella adspersa) (UKBAP)
Saline lagoons (UKBAP)
Interesting fact
The finger-like growths around the edges of a lagoon sea slug’s body have many possible uses, from aiding respiration to defence against predators – they look as though they might sting.
