HOMEPAGE

FOSSILS TERMINOLOGY REFERENCES LINKS
 

BRITISH CHALK ECHINODERMS

 

Marsupites testudinarius, image © Booth Museum

Calliderma smithae, image © Booth Museum

Crinoids (Sea Lilies)

Asteroids (Starfish)

Ophiotitanos tenuis, image © Booth Museum

Micraster normannaie

Ophiuroids (Brittle Stars)

Echinoids (sea Urchins)

   
Introduction    

The Echinoderms are a major division of the animal kingdom, and a highly important component of the British Chalk.  Echinoderms have several unifying characters;

- The skeleton is composed of many calcareous elements, each composed of the unique honeycomb microstructure known as stereom.  Each element (plate, spine, ossicle, etc..) is a single crystal of calcite which is typically recrystallised in the chalk, with the loss of the stereom microstructure. 

- Echinoderms possess a water-vascular system, extensions of which, the tube-feet, protrude through holes in the skeleton and aid in locomotion, feeding and respiration.  Tube feet are organised into rows called ambulacra.  Water enters the system via a sieve-like plate called the madreporite (absent in crinoids). 

- Echinoderms also display penta-radial (five rayed) symmetry, most obvious as the five rows of ambulacra and the five arms of Asteroids (starfish) and Ophiuroids (brittle stars).