The edible or common sea urchin (Echinus esculentus) has a large, rounded 'shell', which is actually an external skeleton, correctly called a 'test', composed of calcareous plates. It is usually pinkish-red in colour but more rarely may be shades of yellow, green or purple (2). The shape of the test varies depending on the depth of the water; those of individuals living in shallow water tend to be more flat than those of individuals living in deep water (3). The Latin name for the genus 'Echinus' derives from the Greek for 'spiny'; the test bristles with many protective reddish spines with lilac coloured tips (2).
The common sea urchin browses on seaweeds and invertebrates(2), moving along the sea floor by means of 'tube feet', which project out from the spines (4). The mouth is located centrally on the underside of the test, and is furnished with a group of 5 specialised calcareous plates, known as an 'Aristotle's lantern' which acts as a jaw (4).
The sexes are separate, breeding takes place in spring, and fertilisation is external (3). A microscopic four-armed larval stage forms; this 'echinopluteus' larva is free-swimming and makes up an important part of the plankton for around 8 weeks, before undergoing a complex metamorphosis into a small urchin (3). Maturity is reached at between one and three years of age, and estimates of maximum lifespan vary from 10 to 16 years of age (3).
Although widespread and common in much of Britain, the edible sea urchin is absent from some areas of north Wales, the east coast of England and the eastern part of the English Channel (2). It has a broad range in northwest Europe (3), from Finland and Iceland in the north, reaching south to Portugal (2).
Occasionally may be found on the lower shore, but highest densities occur offshore (3), where it lives on rocky surfaces (2). It usually reaches depths of around 40 metres, but has been found at over 100 metres deep (2).
The common and scientific names suggest that this sea urchin is edible (esculentus is the Latin word for 'edible'), yet only the reproductive organs (roe) can be eaten (5). There is a large international market for sea urchin products, particularly the roe (6). Exploitation of sea urchins grew rapidly in many countries, and in many cases over-exploitation and collapse of the sea urchin populations followed (6). There was a sea urchin fishery in Cornwall in the 1980s, and the potential of a fishery in Shetland has been investigated (2). The edible sea urchin has also been collected commercially for the curio trade (2).
The fusion of gametes (male and female reproductive cells) to produce an embryo, which grows into a new individual.
Animals with no backbone, such as insects, crustaceans, worms, molluscs, spiders, cnidarians (jellyfish, corals, sea anemones), echinoderms, and others.
Stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
Of the stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
An abrupt physical change from the larval to the adult form.
Aquatic organisms that drift with water movements; may be either phytoplankton (plants), or zooplankton (animals).
Tyler-Walters, H., 2000. Echinus esculentus. Edible sea urchin. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. (August, 2002) http://www.marlin.ac.uk/species/Echinusesculentus.htm
Fish, J.D. and Fish, S. (1996) A student's guide to the seashore. Second Edition. Cambridge University Press, Cambridge.
Burnie, D. (2001) Animal. Dorling Kindersley, London.
Buczacki, S. (2002) Fauna Britannica. Hamlyn, London.
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