X 



CHAPTER XVI. 



PHYLUM BRACHIOPODA.* 



Fixed, solitary, apparently unsegmented Coelomata, with a ten- 

 taculated ljuccal groove often prolonged into arms, and a bivalve 

 shell. 



The Brachiopoda constitute an isolated phylum of the animal 

 kingdom. They were formerly placed with the Mollusca, with 

 which they have clearly no affinities. Later they were associated 

 with the Polyzoa under the heading Molluscoidea ; but this grouping 

 must also be regarded as unsatisfactory, for they differ from the 

 Polyzoa in several important points, amongst which may be men- 

 tioned the presence of a vascular system, of paired nephridia, of 

 setae embedded in pits of the skin, of a shell composed of two 

 pieces, and in not forming colonies. 



On the whole, the increased knowledge of their anatomy and 

 development which has been acquired of late years, though still 

 far from satisfactory, points to the view that we must assign to 

 the group the position of an independent phylum of the animal 

 kingdom with affinities, by the form of their central nervous system, 

 and by their setae, by the presence of a well-developed perivisceral 

 coelom and a canalicular haemocoel, and by the traces of an 

 imperfect segmentation, to the Annelida; though at the same time 

 it must be pointed out that by the presence of longitudinal dorsal 



* K. Owen, "On the Anatomy of the Brachiopoda," Trans. Zool. Soc. London 

 1835. A. Hancock, "On the Organisation of the Brachiopoda," Phil. Trans. 

 148, London, 1858. T. Davidson, "A Monograph of the British Fossil Brachio- 

 poda," I. -VI., Palaeontographical Society, London, 1851-84. Id., "A Mon. 

 of recent Brachiopoda," Pts. 1, 2, Trans. Lin. Soc. London, 1885-8. T. H. 

 Huxley, "Contributions to the Anatomy of the Brachiopoda," Proc. Roy. Soc., 

 7, 1854 (2), 14, 1854. H. Lacaze-Duthiers, " Histoire Nat. d. Brachiopodes de 

 la Mediterranee," Ann. Sci. Nat. (4), 15, 1861. J. F. van Bemmelen, " Unters. 

 lib. d. Anat. u. hist. Bau d. Brachiopoda Testicardinia," Jen. Zeits., 16, 1883. 

 A. E. Shipley, "On the Structure and Devel. of Argiope," Mil. Zool. Stat. 

 Neapel, 4, 1883. A. E. Shipley and F. R. C. Reed, "Brachiopoda Recent and 

 Extinct," in Cambridge Natural History, vol. 3, 1895. 



