CHAPTER XII 
BRACHIOPODA 
Ecardines—Lingula, Crania, Discina. 
EE EERUSEOES Testicardines—Argiope, Terebratula, Waldheimia. 
CHARACTERISTICS.—Coclomata devoid of organs of locomotion, and 
usually fixed in the sand on to some foreign body, by a 
peduncle. A bivalved shell encloses the body. The valves 
are dorsal and ventral, and in one subdivision are hinged to 
one another. They are lined by dorsal and ventral extensions 
of the body-wall, termed the mantles ; these often bear chitin- 
oid setae round their edges. A lophophore surrounds the 
mouth, bearing ciliated tentacles. The alimentary canal is 
ciliated, and receives the secretion of two branched glands, the 
liver ; it is in one sub-division aproctous. One, rarely two, 
pair of nephridia exist. Exclusively marine. 
The existing Brachiopoda are interesting as the survival of 
what in early geological time was a 
very widely distributed and very numer- 
ous group of animals. The two genera 
Lingula and Discina extend from the 
Cambrian, the oldest group of the 
Silurian rocks, to the present day; and, 
judging by their shells, they appear to 
have undergone but little change during 
the vast period of time which must 
have elapsed since they lived. They are 
found in great numbers, both of indi- 
viduals and of species, in these older 
Fic. 106.— Waldheimia 
cranium. 
A. Ventral, 
B. Dorsal valve. 
Paleozoic formations; but the group seems to have been most 
flourishing in the Devonian seas, for upwards of 60 genera and 
