BRACHIOPODA 



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surrounds the alimentary canal communicates with the 

 mantle-cavity by means of 

 two, or rarely four, funnel- 

 shaped canals, which serve 

 as excretory organs. The 

 body-cavity extends into the 

 mantle as a series of spaces 

 or sinuses ; these produce 

 slight depressions on the 

 interior of the valves, and 

 can often be traced as ridges 

 on the internal casts of fossil 

 specimens (tig. 85). The 

 body-cavity is filled with a 

 fluid which is kept in motion 

 by means of cilia. A vesicle 

 found on the dorsal surface 

 of the alimentary canal, near 

 the oesophagus, is regarded as the heart. 



The brachiopods are never colonial animals. Repro- 

 duction takes place sexually, and the sexes are separate. 

 The genital organs are placed in the body-cavity, and in 

 the sinuses of the mantle. 



Generally the greater part of the mantle-cavity is 

 occupied by two long processes, given off from the sides 

 of the mouth ; these are known as the " arms " (fig. 69, d), 

 since they were at first supposed to serve in locomotion — 

 hence the name Brachiopoda. The arms are covered with 

 cirri (h), which produce a current of water conveying food 

 to the mouth. Respiration is carried on mainly by the 

 mantle, but possibly also to some extent by the arms. 



Of the two valves of the brachiopod, the ventral is 

 nearly always larger than the dorsal ; each is produced 



Fig. 69. Magellania [ = Wald- 

 heimia~\Jlavesceiis, Recent. Lon- 

 gitudinal section. d, (upper), 

 cardinal process ; d, (lower), 

 arms ; h, cirri ; a, adductor 

 muscles ; c, c', divaricator mus- 

 cles ; ss, septum ; v, mouth ; z, 

 terminal part of alimentary 

 canal. (After Davidson.) x l|. 



w. p. 



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