Sea lemon  (Archidoris pseudoargus)

Common and widespread (2).

The sea lemon, Archidoris pseudoargus (also known as Archidoris tuberculata in much of Europe) (3) is a common sea slug around Britain (4). It has an oval shaped body (2) and varies greatly in colour. Yellow, pink, green, white and brown forms are known, and there is also a brilliant red variety known as Archidoris pseudoargus var. flammea (4). It is usually mottled to a degree, which may act as camouflage (4). The upper surface of the sea lemon is covered in bumps called 'tubercles', and a ring of 8-9 retractable feathery gills is located towards the rear (2). This species may be confused with the similar Geitodoris planata, which can be identified by the presence of brown spots on the underside, and star-like spots on the upper surface (4).

Common around the coastline of Britain (2); elsewhere it is found from Iceland to the Mediterranean (4).

You can view distribution information for this species at the National Biodiversity Network Gateway.

Occurs on the lower shore underneath large rocks, and extends offshore to depths of around 300m (2).

The sea lemon feeds mainly on the bread-crumb sponge Halichondria panicea and other sponges (4). It is hermaphroditic, possessing both male and female organs. Breeding occurs in the spring (5); thousands of eggs are produced in a long mass, which is attached to rocks and looks like a coiled whitish or yellowish ribbon (5).

The larvae are free-swimming, and hatch after around four weeks. This pelagic stage lasts for around three months; larvae then undergo metamorphosis and become adults. It is thought that metamorphosis is triggered by the larva coming into contact with Halichondria sponges (5). Individuals are known to have lived to around 1 year of age, although they may live longer (5).

Not currently threatened (2).

Conservation action has not been targeted at this species.

There may be further information about this species available via the National Biodiversity Network Gateway.

For more on this species, and other British sea slugs, see:

• Nudibranchs of the British Isles:
  http://www.seaslug.org.uk/nudibranchs/

For more on sea slugs, see:

• Sea Slug Forum:
  http://www.seaslugforum.net/