CLASS II 



BRACHIOPODA 303 



margin of the ventral valve. In derived forms this is progressively closed posteriorly ; 

 geologically in the phylum, and ontogenetically in the latest derived individuals. 



Habitat and Distribution. Brachiopods are usually gregarious in 

 habit, often growing in clusters attached to one another. This is not only 

 true of recent species, but of Palaeozoic forms as well. Brachiopods are found 

 in all latitudes and at all depths, occurring most abundantly between tides 

 and 278 fathoms. Liothyrina Wymllii was dredged from the enormous depth 

 of 2945 fathoms. Terebratulina caput-serpentis ranges from a few fathoms to 

 a depth of 1195 fathoms. 



Brachiopods are most prolific in warmer seas, the Japanese province having 

 nearly thirty species. As a rule, those occurring in cold waters are not found 

 in warm waters. Oehlert has shown, however, that a few species are world- 

 wide in their distribution (Liothyrina mtrea, var. minor and Terebratulina caput- 

 serpentis), and that they also have great bathymetric range. Some generally 

 distributed Palaeozoic species are Atrypa reticularis, Leptaena rhomboidalis, and 

 Product us semireticulatus. 



Migration of Brachiopods is possible only during the early larval stages, 

 and then to a very limited extent. Morse observed that Terebratulina became 

 attached in a few days, but Miiller kept Discinisca in confinement nearly a 

 month before any became sessile. Deep-sea Brachiopods are usually thin- 

 shelled, brittle, and translucent. 



Colour. " The shells of most living species are of light or neutral tints, 

 white or horn-colour. A deep orange-red in radiating bands or in solid tints, 

 colours some species (Terebratulina, Kraussina, etc.) ; light yellows, deep and 

 light shades of green (Lingula), black in bands (Crania), or masses (RJiyncJumella) 

 embellish these shells. Even among the fossil species traces of faded colour- 

 marks are occasionally observed ; Deslongchamps has described them among 

 Jurassic species, Davidson among the Carboniferous, and Kayser has found a 

 colour-marked Rhynchondla in the Devonian. The large highly ornamented 

 species of Palaeozoic times, with their external sculpture heightened by a 

 brilliant colouring, must have been objects of exquisite beauty " (Hall and 

 Clarke). 



Classification. The Brachiopoda, since 1858, have been divided by 

 nearly all systematists into two orders, based on the presence or absence of 

 articulating processes. These divisions, " Artieules and Libres," were recog- 

 nised by Deshayes as early as 1835, but not until twenty-three years later 

 were the names Lyopomata and Arthropomata given them by Owen. These 

 terms have been generally adopted by writers, though some prefer Inarticulate 

 and Articulata, Huxley, or Bronn's Ecardines and Testicardines. Bronn (1862) 

 and King (1873), while retaining these divisions, considered the presence or 

 absence of an anal opening more important than articulating processes, and 

 accordingly proposed the terms Pleuropygia and Apygia, and Tretenterata and 

 Clistenterata respectively. In many Palaeozoic rostrate genera of Clistenterata, 

 it has been shown that an anal opening was also present, and therefore the 

 absence or presence of this organ is not of ordinal value. 



The first attempt to construct a classification of the Brachiopods was that 

 of Leopold von Buch, who took for his principal differential characters the 

 conformation of the umbonal region, the presence or absence of a pedicle, the 

 nature of the delticlium, and the external form and ornamentation of the shell. 



