ERYOWA 



227 



dantly preserved as fossils. Like the much more primi- Antiquity of 

 tive sponges, they represent an isolated type, which has 

 produced a great number of genera and species, without 

 showing much real progress. 



BRACHIOPODA 



I. The nearest relatives of the Bryozoa are the so- structure of 

 called lampshells or Brachiopoda. They are exclusively Brachi P da 

 marine, and today are relatively rare, fewer than 200 

 species being known. In Palaeozoic times they were 

 extremely numerous, and thousands of forms have been 

 made known from the fossil remains. The name "lamp- 

 shell" is derived from the fact that in typical forms the 

 bivalved shell, more or less oval in form, shows an open- 

 ing at one end for the pedicel by which the animal is at- 

 tached to a rock or some other solid object. The shell 

 consequently resembles a Roman lamp, such as those 

 recovered at Pompeii, the opening corresponding to that 

 for the wick. For many 

 years the Brachiopoda 

 were classified as mol- 

 lusks, but the most super- 

 ficial examination of the 

 internal organs shows that 

 this is entirely erroneous. 

 On opening the shell we 

 find the variously coiled or 

 twisted brachidia, which 

 support the brachia or 

 fleshy arms ; the latter 

 possess a respiratory func- 

 tion, and also set up cur- 

 rents of water which serve 



From Nicholson's " Classifica- 

 tion of the Animal Kingdom " 



FIG. 55. Brachiopods. A, B, Lingula; 

 C, Waldheimia ; D, Isocrania. p, pedun- 

 cle; v, ventral valve; d, dorsal valve; s, 

 sand particles inclosing end of peduncle. 



