OTHER UNSEGMENTED WORMS 



193 



223. Phylum Brachiopoda. — The animals included in Brachiopoda 

 (brak i op' o da; G., brachion, arm, and podos, foot) resemble certain 

 mollusks in that they possess a bivalve calcareous shell (Fig. 106). For 

 that reason they have in the past been generally considered as belonging 

 to the field of conchology, the science which deals with the mollusks. 

 They have also been frequently grouped with the Bryozoa in a phylum 

 called Molluscoidea. The brachiopods, however, differ from the bivalve 

 mollusks in that the two valves of the shell are dorsoventral and not 

 lateral and that the internal structure is more wormlike than mollusk- 

 like. They are often called lamp shells because of the resemblance of 

 the shell, when viewed from the side, to an antique lamp. The ventral 



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Fig. 107. — Semidiagrammatic longitudinal section of a brachiopod, Magellania 

 lenticularis. {From VanCleave, "Invertebrate Zoology," after Parker and Haswell, by the 

 courtesy of the McGraw-Hill Book Company, Inc.) 



valve is larger than the dorsal one and at the margin where the two 

 articulate extends beyond the other, forming a beak. The tip of this 

 beak is pierced by an opening, or foramen, through which is passed a 

 fleshy peduncle which permanently attaches the animal to some object. 



Brachiopods also possess a lophophore (Fig. 107), which consists of 

 two coiled arms bearing many ciliated tentacles. The function of this 

 lophophore, as in the Bryozoa, is to collect food and draw it into the 

 mouth. A true coelom is present. The animal possesses a heart and 

 blood vessels. 



The brachiopods are all marine and have lived in the seas since very 

 ancient times. In past ages they have been more abundant than at 

 present, but many of them have come down to us practically unchanged. 

 One, Ldngula, lives in the seas today and exhibits the same characteristics 

 as it did in the Silurian period, which, according to different estimates, 

 was anywhere from 25,000,000 to 300,000,000 years ago (Fig. 371). 



