GENERAL ZOOLOGY 



Digestive 

 gland 



Stomach 



Arteries Coelomic funnel 



"Heart" /("nephridium") 



Arm of 

 lophophore 



Peduncle 



Upper valve 



Adductor 

 muscle 



Lower valve 



Divaricator 

 muscle 

 Esophagus 



Mantle cavity 



Mouth 



Coelomic canal 

 of lophophore 



Fig. 12.15. Lateral view of a brachiopod, Magellama flavescens, partially dissected from the 

 left side to show general arrangement of internal organs. The left arm of the lophophore has 

 been removed, along with other structures. Magellama is generally similar to Terebralulina 

 {cj. Fig. 12.14). (Redrawn from A. Hancock, 1858, Philosophical Transactions of the Royal 

 Society of London, vol. 148.) 



and fits like a lid upon the lower (Fig. 12.15). The short stalk extends 

 upward through the posterior margin of the lower valve, then curves abruptly 

 downward to the substrate. Internally, the most conspicuous feature is the 

 horseshoe-shaped lophophore, which bears ciliated tentacles and occupies a 

 large part of the cavity between the valves. The arms of the lophophore 

 converge upon the mouth, and ciliated grooves in these arms conduct micro- 

 scopic food particles into the mouth opening. The mouth leads into a simple 

 digestive cavity consisting of gullet, stomach, and intestine. Both stomach 

 and intestine are provided with branching digestive glands. As previously 

 indicated, an anus is lacking in Terebralulina and its relatives. A circulatory 

 system is present, with extensive ramifications throughout the body and into 

 the tentacles. Coelomic sinuses, lined by a ciliated peritoneum, also permeate 

 the body, and the function of circulation is probably shared to some extent 

 between the coelomic fluid and the blood. The nervous system is simple, 

 consisting of a nerve ring surrounding the gullet and giving off numerous 

 branches. The gonads are branched organs occupying coelomic sinuses in the 

 mantle flaps lining the valves. Sexes are separate. Eggs or sperms are dis- 

 charged into the coelom and make their way to the outside through a pair of 

 ciliated funnels often termed nephridia. Whether these organs actually 

 function as nephridia, or whether their chief function is that of gonoducts, is 

 open to question. Fertilization is external, although development into a 

 ciliated, free-swimming larva may occur within the mantle cavity of the 



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