They exist in the Brachiopoda (which are probably not unrelated to the Chaetopoda), but otherwise are absolutely distinctive of the Chaetopods.
BRACHIOPODA, an important and well-defined but extremely isolated class of invertebrates.
In a later scheme based on our increased knowledge of fossil forms, the Brachiopoda are divided into four primary groups (orders).
22) shows that it consists of a stout base, composed of a very hyaline connective tissue not uncommon in the tissues of the Brachiopoda, which is traversed by certain canals whose nature is considered below under the section (The Body Cavity) devoted to the coelom.
The number and position of the muscles differ materially in the two great divisions into which the Brachiopoda have been grouped, and to some extent also in the different genera of which each division is composed.
Unfortunately almost every anatomist who has written on the muscles of the Brachiopoda has proposed different names for each muscle, and the confusion thence arising is much to be regretted.
Such is the general arrangement of the shell muscles in the division composing the articulated Brachiopoda, making allowance for certain unimportant modifications observable in the animals composing the different families and genera thereof.
(After King.) and sockets, many species of Brachiopoda could open their valves but slightly.
Soc. xli., 1902), little real advance has been made in our knowledge of the embryology of the Brachiopoda within recentears.
Beecher's division of the Brachiopoda into four orders is based largely on the character of the aperture through which the stalk or pedicle leaves the shell.
Little light has been thrown on the affinities of the Brachiopoda by recent research, though speculation has not been wanting.
A full bibliography of Brachiopoda (recent and fossil) is to be found in Davidson's Monograph of British Fossil Brachiopods, Pal.
The Monograph on Recent Brachiopoda, by the same author, Tr.
' Classes: Cephalopoda, Gasteropoda, Pteropoda, Lamellibranchiata, Brachiopoda, Tunicata.
Classes: Polyzoa, Brachiopoda, Tunicata.
Thompson, 1830) synonymous with Bryozoa (Ehrenberg, 1831) for a group commonly included with the Brachiopoda in the Molluscoidea (Milne Edwards, 1;843).
Hatschek (1888) treated the Entoprocta as a division of his group Scolecida, characterized by the possession of a primary body-cavity and of protonephridia; while he placed the Ectoprocta, with the Phoronida and Brachiopoda, in a distinct group, the Tentaculata.
In the animal kingdom it occurs as both calcite and aragonite in the tests of the foraminifera, echinoderms, brachiopoda, and mollusca; also in the skeletons of sponges and corals.
From a study of remains of the mollusca, brachiopoda and other marine organisms they will determine the shallow water (littoral) and deep water (abyssal) regions of the surrounding oceans, and the clear or muddy, salt, brackish or fresh character of its inland and marginal seas; and even the physical conditions of the open sea at the time will be ascertained.
L * An independent anatomical investigation of the Mollusca had been carried on by the remarkable Neapolitan naturalist Poli (1791), whose researches 2 were not published until after his death (1817), and were followed by the beautiful works of another Neapolitan zoologist, the illustrious Delle Chiaje.3 The embranchement or sub-kingdom Mollusca, as defined by Cuvier, included the following classes of shellfish: (1) the cuttles or poulps, under the name Cephalopoda; (2) the snails, whelks and slugs, both terrestrial and marine, under the name Gastropoda; (3) the sea-butterflies or winged-snails, under the name Pteropoda; (4) the clams, mussels and oysters, under the name Acephala; (5) the lamp-shells, under the name Brachiopoda; (6) the seasquirts or ascidians, under the name Nuda; and (7) the barnacles and sea-acorns, under the name Cirrhopoda.
Henri Milne-Edwards in 1844 demonstrated the affinities of the Polyzoa with the Molluscan class Brachiopoda, and proposed to associate the three classes Brachiopoda, Polyzoa and Tunicata in a large group " Molluscoidea," co-ordinate with the remaining classes of Cuvier's Mollusca, which formed a group retaining the name Mollusca.
The development of Phoronis was supposed by Caldwell (2) to furnish the explanation of the relations of the surfaces in Brachiopoda, Polyzoa and perhaps the Sipunculoid Gephyrea, in which the ontogenetic evidence is less clear.
The peduncle of the Brachiopoda was supposed to correspond with the everted ventral sac of Actinotrocha, but the question is complicated by the want of any complete investigation of the development of the Brachiopoda, and by the absence of the anus in the majority of the genera.
The conception of the Dipleurula derives its chief weight from the fact that it is comparable to the early larval forms of other primitive coelomate animals, such as Balanoglossus, Phoronis, Chaetognatha, Brachiopoda and Bryozoa.
The most that can be said is that the Chaetognaths begin life with three segments, a feature they share with such widelydiffering groups as the Brachiopoda, the Echinoderma and the Enteropneusta, and probably Vertebrata generally.
By subsequent writers the Polyzoa have in some cases been kept apart from the Mollusca and classed with the " Vermes "; whilst by others they have, together with the Brachiopoda, been regarded.as true Mollusca.
Increase of knowledge has now, however, established the conclusion that the agreement of structure supposed to obtain between Polyzoa and true Mollusca is delusive; and accordingly they, together with the Brachiopoda, were removed from the Molluscan phylum by Lankester in his article in the 9th edition of this work (on the which present article is based).