258 



THE INTERMEDIATE GROUP, MOLLUSCOIDA, 

 THE MANTLE-BREATHING BIVALVES (BRACHIOPODA) AND THE MOSS-ANIMALS * (BRYOZOA). 



THE BRACHIOPODA Life History and Characters of the Brachiopoda Origin of the Name Subdivision of the 

 Group Its Relations to other Organisms Growth and Structure of the External and Internal Skeleton Muscles 

 Organ of Attachment Mantle Gills Digestive, Generative, and Nervous Systems How the Brachiopoda Live- 

 Classification and Anatomy of Minor Groups Distribution in Space and Ranges of Depth of Living Forms Fossil 

 Genera Embryology and Affinities THE BRYOZOA* Life History of the Moss-animals Name and Position of the 

 Group Its Chief Subdivisions The Colonial Skeleton The Individual Moss-animal Muscles and their Action- 

 Respiratory, Circulatory, and Reproductive Systems Structure and Functions of the Appendicular Organs Classi- 

 fication and Anatomy of Minor Groups Geographical and Bathymetrical Distribution of Marine and Fresh-water 

 Genera Geological Range Reproduction of the Colony and of the Individual Embryological History Affinities and 

 Systematic Position of the Brachiopoda and Bryozoa. 



ALL the Brachiopoda, f or mantle-breathing bivalves, are exclusively inhabitants of the ocean. 

 They are found attached to stones, rocks, corals, sponges, sea-mats, and sea-weeds, or adhering to 

 each other in masses, in shallow water, and are dredged from considerable depths. The class a very 

 extensive one comprises about one hundred and thirty genera, and between four and five thousand 

 species. By far the greater number of these are extinct forms ; but the one hundred and thirty 

 existing species merit consideration as the surviving members of a most ancient but now declining 

 race. For these lowly molluscs were among the first representatives of life in the ancient seas of 

 our planet, during remote geological ages. 



The first figures and descriptions of members of this group were given by Prince Fabio Colonna 

 in 1606. But the animals were for many years confounded with the 

 " plate-gilled " bivalves (Lamellibranchiata) already described (p. 230), 

 and the great Cuvier was the first to recognise their distinctive charac- 

 ters. He constituted a separate class for the reception of the 

 Brachiopoda, signifying " arm-footed," under the impression that 

 some largely-developed internal organs which occupy the greater 

 portion of the interior of the shell the so-called " arms " or " feet," 

 which are the special characteristic of these organisms -were used 

 as feet, and employed in the processes of locomotion. It is now 

 known that these organs, although capable of protrusion, in some 



Fig. I.-TEREBRATULA cuBExsis g 6116 . beyond the marginal or outer edges of the shell, are never 

 ATTACHED TO CORAL AT A DEPTH really used for locomotion. De Blainville's subsequently proposed 

 OF 420 FATHOMS OFF ASCEXSION. title of mantle-breathers, " J referring to the respiratory function 



(After Davidson.) (" Challenger' Ex- 



petition.) exercised by the pallium or mantle the delicate membranous internal 



lining of the shell is therefore used by some naturalists. But the first name enjoys the right 

 of priority and long habit, and as Brachiopoda these animals will probably ever be better known, 

 although they never walk iipon their so-called arms or feet. 



In fact, their powers of locomotion are somewhat limited, being restricted, in most genera, to 

 a free movement on the muscular stalk or peduncle. Members of one 

 genus, however, jerk themselves about by the sliding action of their 

 valves, swinging the fringes of setae, or minute bristles edging the 

 mantle, to and fro like the oars of a galley, and leaving a peculiar 

 track in the sand. Young individuals, in the earlier stages of growth, 

 are quite free and unattached, swimming actively about in the water. 

 Others were fixed during a portion of their lives, the opening for 

 the peduncle subsequently becoming closed. A few of the fossil 

 forms show no marks of attachment, and are believed to have always 

 enioved a free existence Fig ' 2 '~~ I)I8CI5ri8CA LAMKLLOSA. 



er W e< OFF CALLAO, PERU. (After Davidson.) 



The Brachiopoda were also called Lampades, or lamp-shells, by the 

 older naturalists, the shape of the shell, and the hole serving for the passage of the peduncle, suggest- 



* Greek, bruon, moss ; zoon, an animal. t Greek brachion, an arm ; pous, the foot. 



+ Palliobranchiata, Lat., pallium, a mantle ; Greek, branchia, gills. 



