266 BRACHIOPODA 



the anus is at the hinder end of the body between the edges of the shells. 

 The nervous system consists of a pair of ganglia dorsal to the oesophagus, 

 a ventral pair, connecting commissures and radiating nerves. There are 

 no special sense organs in the adult animal, although the larva may have 

 eye spots and otocysts. The circulatory system consists of a heart, a large 

 vein which enters it anteriorly, and arteries which proceed to the spaces 

 of the body cavity. The excretory organs consist of a pair (two pairs in 

 Rhynchonella) of nephridial tubes which open into the body cavity at one 

 end and into the mantle cavity at the other. The sexes are as a rule sep- 

 arate. The two pairs of genital glands lie near the intestine and discharge 

 their products into the body cavity, whence they find their way to the 

 outside through the nephridia. The larva is a trochophore, and is made 

 up of three divisions, from the middle one of which the mantle folds 

 develop: after a few hours of free life the larva attaches itself. 



Habits and Distribution.* All Brachiopoda are attached to rocks, or 

 other similar objects, except the Lingulidae, which live in vertical burrows 

 in the sand. Most of the species live in shallow water in the neighbor- 

 hood of continents : a few, however, are found in the deep sea. They are 

 not generally distributed over the world but are localized, as is the case 

 with many ancient groups of animals, but are often found in large num- 

 bers where they do occur. Brachiopods have flourished during all the 

 geological ages from the Cambrian down to the present time, the genus 

 Lingula, which is still plentiful in the Indian and Pacific Oceans, being 

 the oldest known genus of animals. About 2,500 fossil species have been 

 discovered, mostly in the Paleozoic rocks, only about 120 living species 

 being known. 



History.] The conspicuous shells of the Brachiopoda attracted the 

 attention of the older naturalists, by whom the animals were almost uni- 

 versally regarded as mollusks. The name Brachiopoda was given them 

 in 1807 by Dumeril. In 1873 and 1874 Morse and Kowalevsky independ- 

 ently demonstrated by a study of their embryology that the affinities of 

 brachiopods were not with the Mollusca but rather with the Annelida. 

 Brooks held them to be Bryozoa, while Huxley and Claus placed them 

 among the Molluscoidea, a subkingdom or phylum originally created by 

 Milne-Edwards to contain the Bryozoa and Tunicata. Conklin and others 



* See "Observations on Living Brachiopoda," by E. S. Morse, Mem. Bost. Soc. 

 Nat. Hist., Vol. 5, 1902. 



t See "On the Embryology of Terebratulina," by E. S. Morse, Mem. Bost. Soc. 

 Nat. Hist, Vol. 2, 1873. "On the Systematic Position of the Brachiopoda," by E. S. 

 Morse, Proc. Bost. Soc. Nat. Hist., Vol. 15, 1873. "On the Development of the 

 Brachiopoda," by A. Kowalevsky, Abst., by A. Agassiz, Am. Jour. Sci., 1874. "Th 

 Development of Lingula and the Systematic Position of the Brachiopoda," by W. K. 

 Brooks, Sci. Results of Sess. of 1878, Chesapeake Zool. Lab. "The Embryology of 

 a Brachiopod," etc., by E. G. Conklin, Proc. Am. Phil. Soc., Vol. 41, 1902. 



