56 



ZOOLOGY. 



Brachiopoda were generally, and still are by some authors, 

 considered to be mollusks, though aberrant in type. The 

 shell of our common northern species, Terebratulina sep- 

 tentrionalis (Fig. 61), which lives attached to rocks in froir; 

 ten to fifty or more fathoms north of Cape Cod, is in shape 

 somewhat like an ancient Soman lamp, the upper and 

 larger valve being perforated at the base for the passage 

 through it of a peduncle by which the animal is attached 

 to rocks. The shell is secreted by the skin, and is com- 

 posed of carbonate {Terebratulina) or largely (Lingula, 

 Fig. 62) of phosphate of lime. It is really the thickened 



Fig. 61.— Terebratulina or lamp-shell. Upper, and side view, natural size. 

 From Emerton, after Morse. 



skin of the animal, the so called mantle being the inner 

 portion of the skin. 



The Brachiopods may be briefly described as shelled 

 worms, with a limestone or partly chitinous, inequivalve, 

 hinged or unhinged shell, enclosing the worm-like animal; 

 with two spirally coiled arms provided with dense ciliated 

 tentacles, and capable of reaching to or beyond the edge of 

 the gaping shell; the alimentary canal has the month open- 

 ing between the arms; there is an oesophagus, a stomach with 

 a liver-mass on each side, and a short intestine ending in a 

 blind sac. The nervous system consists of a ganglion above 

 and beneath the oesophagus, and two lateral ventral widely 

 separated threads. There are no eyes in the adult, but they 

 are present in the young; auditory sacs are present in Lin- 

 gula. There is no circulatory system. The germ passes 

 through a morula and gastrula stage, becoming a segmented 



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