CHAPTER IX 



MOLLUSCOIDEA 



Certain forms known as Brachiopoda and Bryozoa ("Polyzoa" 

 of England), on account of their resemblance to Mollusca, have been 

 grouped under the Phylum Molluscoidea. 



In 1830, J. V. Thompson separated the Bryozoa from the polyps, 

 and called them Polyzoa from their habit of gemmation, and their 

 digestive tube. One year later, Ehrenberg changed the term to 

 Bryozoa. In 1841, Milne-Edwards created the Phylum Mollus- 

 coidea, including it in Bryozoa and Tunicata. Subsequently the 

 Tunicata were removed, and in 1 853, Huxley added the Brachiopoda. 



Class I. — The Brachiopoda (Gr. brachion^ the arm; and pous^ a 

 foot) are strictly marine, being found in all oceans, and occupy a 

 calcareous bivalved shell, the valves of which are dorsal and ventral 

 instead of lateral as in the Lamellibranchs. Once rulers of the sea, 

 it is supposed that the Brachiopoda or " lamp-shells " were notably 

 reduced in numbers by 

 boring molluscs. They 

 are geologically very 

 ancient, Lingula, the 

 oldest known genus of 

 animals, having changed 

 but slightly since the 

 earliest Silurian times. 



Class 2. — The B^-yo- 

 zoa (Gr. bruon^ moss; 

 and 200W, animal) are for 

 the most part colonial, 

 somewhat resembling 

 hydroids. They are 

 sometimes stained and 



sold as " air-plants " but Hydrozoa (page 69) are the common 

 " air plants." They are found in both salt and fresh water. The 

 false coral {Discosoma nidita) is a marine colonial form that encrusts 

 shells and stones until it somewhat resembles coral. It is found 

 in water at least thirty feet deep. (Mayer.) 



127 



° A 



Fig. 54. Statoblast of CristattUa. (After Allman. 

 Courtesy of Macmillan and Co., Ltd.) 



