Brachiopoda

“ The wide distribution and vast abundance of the Brachiopoda throughout the whole series of geological formations make this group of especial importance to the student of the past history of the earth; and the zoologist must always regard the fossil forms with peculiar interest, because they not only largely outnumber the living representatives, but comprise numerous extinct genera, and even families, exhibiting types of structure and characters entirely absent in the modern members of the group. ”

“ Species of the brachiopod genera Lingula and Crania occurring in the Cambrian rocks are indistinguishable from species living today, while two other modern genera of the Brachiopoda, namely, Rhynchonella and Discina, are represented among the fossils found in Mesozoic formations. Terebratulina striata, a fossil species of brachiopod occurring in the rocks belonging to the Cretaceous system, is identical with our modern species Terebratulina caput serpentis. ”

“ It is impossible to come to any satisfactory conclusion as to the position of the group Brachiopoda with relation to the rest of the animal kingdom. They have, in accordance with the views of various investigators, been placed in close connexion with many of the large groups into which the Invertebrates are split up. The Mollusca, the Tunicata, the Polyzoa, the Chaetopoda, the Gephyrea, and of recent times such isolated forms as Phoronis and Sagitta, have all in turn had their claims advanced of relationship to this most ancient group. ”

“ Having finished our short sketch of the Conchifera, we shall now treat of the singular group, Brachiopoda, [11] which some place nearer to the Gasteropoda than the Pteropoda, giving them, in fact, their place. It is out of the province of this work to enter into the physiological arguments of such a question. The days of the Brachiopoda or [390] short-footed animals are past. Of the 1842 [12] species formerly known, a few types of a small number of genera only are left, numbering in all 102. The Terebratulidæ are best represented; there were once 300 or 400 species ”

“ Educated partly in the university at Edinburgh and partly in France, Italy and Switzerland, and early acquiring an interest in natural history, he benefited greatly by acquaintance with foreign languages and literature, and with men of science in different countries. He was induced in 1837, through the influence of Leopold von Buch, to devote his special attention to the brachiopoda, and in course of time he became the highest authority on this group. The great task of his life was the Monograph of British Fossil Brachiopoda, published by the Palaeontographical Society (1850–1886) . ”

“ The modified epithelium in connexion with the ganglia may possibly have some olfactory or tactile function, but beyond this the Brachiopoda would appear to be devoid of eyes, ears, or any other kind of sense organs,—a condition of things doubtless correlated with their sessile habits, and with the presence of a bivalved shell which leaves no part of their body exposed. ”

“ The Molluscoidea, to which phylum belong the Bryozoa and Brachiopoda, would be but imperfectly understood from a morphological standpoint but for the vast number of fossil forms. The Brachiopoda have been estimated to have less than 150 living species, while probably more than 6,000 fossil species have been described. Of the 31 families only 7 have living representatives. We are dependent, therefore, largely on the fossil forms for our knowledge of the morphology of this class. ”

“ Although the Brachiopoda, or "Lamp-shells," are not true mollusca, they are not very far removed from them, and are so often to be found in cabinets that it will not do to pass them over, especially since in past times they were very abundant, an enormous number occurring in the fossil state. Only eight genera are now living. ”

“ Brachiopoda, brak-i-op′o-da, Brachiopods, brak′i-o-pods, n.pl. a class of shelled animals having certain affinities with worms and with Polyzoa, but less with molluscs, provided with two long arm-like processes arising from the sides of the mouth, probably respiratory, and certainly serving to waft little food particles to the mouth. ”

“ The lamp-shells, or Brachiopoda, form an exceedingly ancient group, dating from the lower Cambrian, and surviving at the present day, although in greatly diminished numbers compared to the Palaeozoic epoch, when they far surpassed the now dominant bivalve molluscs.Brachiopods. The group attained its maximum in the Silurian, when, as in the Palaeozoic genera, nearly all the forms belonged to the hingeless section. ”

“ Most of these occur also in the temperate latitudes of Europe and North America, while many are recognised as distinctive types of the same strata nearly all the world over. As showing — 351 — how strongly the former broad distribution of life-forms is contrasted with their present restricted range, Professor Heilprin has cited the Brachiopoda. Taking existing species and varieties as being 135 in number, he remarks that “there is scarcely a single species which can be said to be strictly cosmopolitan in its range, although not a few are very widely distributed ”

“ Meanwhile in 1889 he received the degree of Ph.D. from Yale University for his memoir on the Brachiospongidae, a remarkable group of Silurian sponges; later on he did good work among the fossil corals, and other groups, being ultimately regarded as a leading authority on fossil crustacea and brachiopoda; his researches on the development of the brachiopoda, and on the Trilobites Triarthrus and Trinudeus, were especially noteworthy. In 1892 he was appointed professor of palaeontology in Yale University. He died on the 14th of February 1904. ”

“ When once settled down it has little to fear from the attacks of other animals. The size of its shell relative to its body would deter most animals from regarding it as a desirable article of food, and as far as is known at present the Brachiopoda suffer but little from internal parasites, the only case I know being a minute parasitic Copepod belonging to a new and as yet unnamed genus which I found within the mantle cavity of Cistella (Argiope) neapolitana in Naples. ”

“ Fig. 4. A species of Terebratula (T. diphya, of Lamarck) . The shells of this genus belong to that division of mollusks termed Brachiopoda (arm-feet) , from their having internally two spiral fleshy arms developed from the sides of the alimentary orifice. These organs are supported by shelly processes, curiously modified in different genera, which often occur in a fossil state. Although the fossil Terebratulæ are very numerous, the recent species are but few, and are inhabitants of the seas off Australia. They form two natural groups ”

“ Now it is remarkable that many of these are fossils which occur in more than one stratum,—often, as the brachiopoda, in several—so that they are thus found to be truly characteristic of the Silurian system, or of large thicknesses of it. Other shells are most abundant in particular deposits—as Serpulites longissimus in Upper Ludlow, Pentamerus Knightii in Aymestry rock, Graptolithus Ludensis in Lower Ludlow, Cyathophyllum dianthus in Wenlock limestone, Trinucleus Caractaci in Caradoc, Ogygia Buchii in Llandeilo flags. ”

“ 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. In the Testicardines, of which the genus Terebratula may be taken as an example, five or six pairs of muscles are stated by A. Hancock, Gratiolet and others to be connected with the opening and closing of the valves, or with their attachment to or movements upon the peduncle. ”

“ Now, the Heteropoda or Pterotracheæ and the Pteropoda or Clionæ have projecting processes which act like fins.
The Brachiopoda or Terebratulæ, though unendowed with the power of locomotion, have, as their first name implies, arm-like organs.
The Cirripedia or Lepades, being likewise without the power of continuous motion, possess podoidal or foot-like appendages. In both these families, however, these appendages are nevertheless true motor organs; for by means of them they seize their food, an act which hitherto has been seen to take place neither in the Snails nor Bivalve Mollusca. ”

“ The single articulated class, Crustacea, is by no means rich in any way; with one exception, all its genera are Trilobites, and commonly contain but one species each. The most important class numerically is Brachiopoda, to which one hundred and eight species belong, that is, thirty-one per cent, of the entire series. The families and genera of Cephalopoda are richer in species than those of any other class, averaging sixteen for each family, and ten for each genus. ”

“ When the waters had become sufficiently cool to allow of the existence of organised beings, creation was developed, and advanced with great energy; for it manifested itself by the appearance of numerous and very different species of animals and plants.
Fig. 17.—Paradoxides Bohemicus—Bohemia.
One of the most ancient groups of organic remains are the Brachiopoda, a group of Mollusca, particularly typified by the genus Lingula, a species of which still exist in the present seas; the Trilobites (Fig. 17) , a family of Crustaceans, especially characteristic of this period ”

“ For ten years (1840–1850) he made a detailed study of these rocks, engaging workmen specially to collect fossils, and in this way he obtained upwards of 3500 species of graptolites, brachiopoda, mollusca, crustacea (particularly trilobites) and fishes. ”

“ The blood is a coagulable fluid. Whether it contains corpuscles is not yet determined, but if so they must be few in number. It is a remarkable fact that in Discinisca, although the vessels to the lophophore are arranged as in other Brachiopods, no trace of a heart or of the posterior vessels has as yet been discovered.
Muscles.—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. ”

“ The Tunicata have no shell or hard covering, but are of a pretty firm consistence; they are either fixed to rocks and sea-weeds, or float about freely, and are either solitary, social, or compound. The "Ascidians" are united in groups, and are all connected [Pg 256] by a common stalk or "Stolon," from which they grow by buds.
2. The Brachiopoda. These Molluscs are furnished with a pair of shells, within which the animal lives ”

“ The first one, No. 87, is by Charles Schuchert, and gives a synopsis of the American Fossil Brachiopoda, including a valuable bibliography and synonymy. The richness of North America in well-preserved Palæozoic brachiopods gives Mr. Schuchert's work a special interest. No. 127, by N. H. Darton, is a catalogue and index of contributions to American geology, and while there can be little said of it in the way of a review, the value of a carefully prepared bibliography of geological literature as a reference book for libraries and geological writers can not be overestimated. No. ”

“ Kowalevsky, the celebrated Russian naturalist, has published in Moscow a memoir on the embryology of certain Brachiopoda studied in the Mediterranean, in which he not only fully confirms the embryological studies of Prof. Morse, but indorses the latter's view, that the brachiopods are annelids. In a review of Kowalevsky's memoir, published in the last number of the American Journal of Science and Arts, Mr. ”

“ In Discinisca and Lingula, however, the sub-oesophageal ganglion is not drawn out, but lies medianly; it gives off two posteriorly directed nerves to the stalk, which in Lingula unite and form a substantial nerve. Sense organs are unknown in the adult. The larval forms are provided with eye-spots, but no very specialized sense organs are found in the adult.
The histology of Brachiopods presents some peculiar and many primitive features. As a rule the cells are minute, and this has especially stood in the way of embryological research. ”

“ In the Bradford-Abbas quarry alone have been found as many as fifty species of univalves, many of which belong to the Cotteswolds [8] . There is, however, a large array of new forms in the genera Pleurotomaria, Chemnitzia, Turbo, Trochus, Natica and Solarium; and others abound.
These, like the Ammonites, are in a wonderful state of preservation.
The Brachiopoda are not so numerous as in the Cotteswold district; still the forms met with in the Cephalopoda-bed point also to the high position it occupies in the Inferior Oolite; such are
And others abound. ”

“ The anterior segment broadens and becomes umbrella-shaped; it has a powerful row of cilia round the rim and smaller cilia on the general surface. By the aid of these cilia the larva swims actively, but owing to its minute size it covers very little distance, and this probably accounts for the fact that where brachiopods occur there are, as a rule, a good many in one spot. The head bears four eye-spots, and it is continually testing the ground (fig. 29, A, C) . The second segment grows downwards like a skirt surrounding the third segment, which is destined to form the stalk. ”

“ Crania in life opens its valves by moving upon the straight hinge, without sliding the valve.
The nervous system of Brachiopods has, as a rule, maintained its primitive connexion with the external epithelium. In a few places it has sunk into the connective-tissue supporting layer beneath the ectoderm, but the chief centres still remain in the ectoderm, and the fibrils forming the nerves are for the most part at the base of the ectodermal cells. ”