Modern forms

Echinoids are abundant today, and over 900 extant species have been described. Of these, 25% are spatangoids, 16% cidaroids, 14% clypeasteroids and 14% temnopleuroids. Most are geographically restricted, but they are found in a wide variety of marine habitats, from the equatorial regions right up to the poles, and from the shallow intertidal zone to depths greater than 4500m (diversity decreasing with latitude and depth).

The range of habitats occupied today is probably wider than at any time in the past, a testament to the adaptive innovation of the euechinoids. Of the most primitive of the irregular echinoids only two species remain. The cidaroids have changed little since the first of modern type arose in the Late Triassic - they are often regarded as 'living fossils', remaining as they were many millions of years ago.

A number of echinoid species that can be found aroung the British Isles today are illustrated here (photos with permission of Bernard Picton from his 'A Field Guide to the Shallow-water Echinoderms of the British Isles', see 'literature and web links'.

Echinus esculentus (common sea urchin), Order Camarodonta.

Individual on a rock (mobile, sea-floor dwelling regular echinoid). Note tube feet extending from outer areas of the narrower (ambulacral) segments ('wispy' looking) and test covered in life by spines.

 Strongylocentrotus droebachiensis(northern sea urchin),Order Echinacea.

Where members of this genus are rarely found in the same habitat as sand dollars Strongylocentrotus will attack them - eating marginal spines first, cannibalism is also known to occur!

Paracentrosus lividus (purple sea urchin)

A number of these echinoids living in cavities in limestone rock which they bore themselves by action of the spines and constant rasping of the lantern.

Echinocardium flavescens (yellow sea potato), Order Spatangoida.

This specimen has been dug up out of its burrow in the substratum, spines of different types can be seen

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