Biodiversity & Conservation

Green sea urchin - Psammechinus miliaris

Psammechinus miliaris

Image Sue Daly - Psammechinus miliaris. Image width ca XX cm.
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Distribution map

Psammechinus miliaris recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

Why do the maps differ?

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Psammechinus miliaris is not listed under any importance categories.

Taxonomy icon Taxonomy Taxon English term
Phylum Echinodermata Starfish, brittlestars, sea urchins & sea cucumbers
Class Echinoidea Sea urchins, heart urchins and sand dollars
Authority Gmelin, 1778
Recent synonyms None
Map icon Recorded Distribution in Britain and Ireland All British and Irish coasts. Evenly distributed in the southern North Sea but scarce in northern North Sea.
Habitat information icon Habitat information Found intertidally on rocky shores under stones, boulders and seaweeds especially Saccharina latissima. Also found subtidally in seagrass beds or on mixed coarse bottoms such as muddy sand and gravel.
Text page icon Description An almost round, slightly flattened urchin that grows up to 57 mm in diameter (although more typically to 35 mm diameter). It is greenish in colour with distinctive violet tips to the spines. The spines are robust, short and closely packed.
Identifying features
  • Test sub-pentagonal and slightly depressed, with short, robust spines.
  • Greenish in overall colour with violet tips to the spines
  • Ambulacral plates have three pore pairs and one primary tubercle.
  • Globiferous pedicellariae abundant, jaw blades grooved, with a row of sharp spines along each side.
Additional information icon Additional information
  • Sometimes called the purple tipped sea urchin. Older publications may refer to sea urchins as "burrs" (Hancock, 1957). Strongylocentrotus droebachiensis is also known as the green sea urchin. It is possible for Psammechinus miliaris to be confused with Strongylocentrotus droebachiensis or pale specimens of Paracentrotus lividus.
  • A regular sea urchin with a somewhat flattened test. The colour varies with habitat (Bull, 939; Lindahl & Runnström, 1929; Comely, 1979). Shallow water or littoral individuals are a deep purplish-brown and show no difference between the colour of the test and spines. Those from deeper water tend to be paler in colour, with a light green test and vivid purple spine tips.
  • The tube-feet are arranged in arcs of 3, visible as 3 pairs of pores corresponding with each ambulacral plate on the denuded test.
  • A typical species of bouldered sheltered shores, also found sublittorally in shallow water in sheltered or slightly brackish sites such as sea lochs. Common in the circalittoral on exposed shores in Shetland.
MarLIN would like to thank Dr Maeve Kelly for her comments and significant additions to the review.

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This review can be cited as follows:

Angus Jackson 2008. Psammechinus miliaris. Green sea urchin. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 09/02/2010]. Available from: <http://www.marlin.ac.uk/speciesinformation.php?speciesID=4216>