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).