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mollusca

mollusca Sentence Examples

  • In zoology, the mollusca are divided into cephalous and acephalous (Acephala), according as they have or have not an organized part of their anatomy as the seat of the brain and special senses.

  • Turtle and sea-snakes abound, as do mollusca, of which a few are peculiar, and zoophytes.

  • GASTROPODA, the second of the five classes of animals constituting the phylum Mollusca.

  • For a discussion of the relationship of the Gastropoda to the remaining classes of the phylum, see MoLLUSCA.

  • It will be remembered that, according to Spengel, the osphradium of mollusca is definitely and intimately related to the gill-plume or ctenidium, being always placed near the base of that organ; further, Spengel has shown that the nerve-supply of this olfactory organ is always derived from the visceral loop. Accord ingly, the nerve-supply FIG.

  • time when the fact that the renal organ s,s', Nerves (right and of the Mollusca, as a rule, opens into the left) to the mantle.

  • The general structure of the Molluscan intestine has not been sufficiently investigated to render any comparison of this structure of Patella with that of other Mollusca possible.

  • The histology of the nervous system of Mollusca has yet to be seriously inquired into.

  • In other Pectinibranchia (and such variations are representative for all Mollusca, and not characteristic only of Pectinibranchia) we find that there is a very unequal division of the egg-cell at the commencement of embryonic development, as in Nassa.

  • This is the largest group of Mollusca, including nearly sixty families, some of which are insufficiently known from the anatomical point of view.

  • The Pteropoda, formerly regarded as a distinct class of the Mollusca, were interpreted by E.

  • In deed, were it not for their retention of the characteristic odontophore we should have little or no indication that such forms as Phyllirhoe and Limapontia really belong to the Mollusca at all.

  • Whether the closed primitive shell-sac of the slugs (and with it the transient embryonic shell-gland of all other Mollusca) is precisely the same thing as the closed sac in which the calcareous pen or shell of the Cephalopod Sepia and its allies is formed, is a further question which we shall consider when dealing with the Cephalopoda.

  • In most other Mollusca (Anisopleurous Gastropods, Pteropods and Conchifera) there is a want of such continuity; the primitive shell-sac contributes no factor to the permanent shell, or only a very minute FIG.

  • (After Spengel.) being formed afresh on the surface of the visceral hump. It is, then, in this sense that we may speak of primary, secondary and tertiary shells in Mollusca, recognizing the fact that they may be merely phases fused by continuity of growth so as to form but one shell, or that in other cases they may be presented to us as separate individual things, in virtue of the non-development of the later phases, or in virtue of sudden changes in the activity of the mantle-surface causing the shedding FIG.

  • Herdman, " On the Structure and Functions of the Cerata or Dorsal Papillae in some Nudibranchiate Mollusca," Quart.

  • P. Woodward, Manual of the Mollusca (2nd ed., with appendix, London, 1869); E.

  • Society, 1845); P. Pelseneer, Mollusca.

  • Ray Lankester, " Mollusca," in 9th ed.

  • - Diagrams of the five classes of Mollusca, from the left side.

  • A history of the British forms is given in Gwyn Jeffreys's British Conchology (1862), and by Forbes and Hanley in British Mollusca.

  • For speciegraphical details, see Woodward's Manual of the Mollusca (1875), and Bronn's Tierreich (Weichtiere).

  • Numerous raised beaches and terraces, containing shells of marine mollusca, &c., occur along the whole coast of Greenland, and indicate that the whole of this large island has been raised, or the sea has sunk, in post-glacial times, after the inland ice covered its now icebare outskirts.

  • " Conchiolin," the matrix of shells of the mollusca, is only slightly soluble in acids.

  • Brachiopods have been at various times placed with the Mollusca, the Chaetopoda, the Chaetognatha, the Phoronidea, the Polyzoa, the Hemichordata, and the Urochordata.

  • Associated with Ray in his work, and more especially occupied with the study of the Worms and Mollusca, was Martin Lister (1638-1712), celebrated also as the author of the first geological map.

  • Mollusca.

  • Animalia Mollusca.

  • He upset (1830) Cuvier's retention of the Cirripedes among Mollusca, and his subsequent treatment of them as an isolated class, by showing that they begin life as free-swimming Crustacea identical with the young forms of other Crustacea.

  • Malaeozoaria or Mollusca.

  • Mollusca proper.

  • Mollusca (q.v.).

  • This appears to indicate B that the Polyzoa are remotely allied to other phyla in which this type of larva prevails, and in particular to the Mollusca and Chaetopoda, as well as to the Rotifera, which are regarded as persistent Trochospheres.

  • These, like the mollusca, indicate the influence of the Kuro Shiwo and the south-west monsoon, for they have close affinity with species found in the Indian and Pacific Oceans.

  • Malta has several species of zoophytes, sponges, mollusca and crustacea.

  • de Pourtales pointed out in 1870; they consist of remains of deep-sea corals, serpulae, echinoderms and mollusca united Sands, gravels, muds, &c.

  • Murray and Renard define globigerina ooze as containing at least 30% of calcium carbonate, in which the remains of pelagic (not benthonic) foraminifera predominate and in which remains of pelagic mollusca such as pteropods and heteropods, ostracodes and also coccoliths (minute calcareous algae) may also occur.

  • The phosphate beds contain Eocene fossils derived from the underlying strata and many fragments of Pleistocene vertebrata such as mastodon, elephant, stag, horse, pig, &c. The phosphate occurs as lumps varying greatly in size, scattered through a sand or clay; they often contain phosphatized Eocene fossils (Mollusca, &c.).

  • He was also author (with John Lycett) of A Monograph of the Mollusca from the Great Oolite (Palaeontographical Soc., 1850-1853).

  • 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.

  • In the latter respect, and in the fact that they frequently develop by a metamorphosis, they approach the Mollusca, but they differ from that group notably in the occurrence of metameric segmentation affecting many of the systems of organs.

  • 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.

  • Ope yxta, gills), the fourth of the five classes of animals constituting the phylum Mollusca.

  • It, as in other Mollusca, is not a blood-space but develops from the coelom, and it communicates with the exterior by the pair of renal tubes.

  • As in Cephalopoda (and possibly other Mollusca) water can be introduced through the nephridia into this space.

  • They are totally distinct from the cephalic eyes of typical Mollusca, and have a different structure and historical development.

  • 21), so that its fibres join the anterior faces of the nerve-end cells as in Vertebrates, instead of their posterior faces as in the cephalic eyes of Mollusca and Arthropoda; moreover, the lens is not a cuticular product but a cellular structure, which, again, is a feature of agreement with the Vertebrate FIG.

  • Peck, " The Minute Structure of the Gills of Lamellibranch Mollusca," Quart.

  • iii.; Paul Pelseneer, " Mollusca," Treatise on Zoology, edited by E.

  • MOLLUSCA, one of the great " phyla," or sub-kingdoms, of the animal pedigree or kingdom.

  • The shell-bearing forms belonging to this group which were known to Linnaeus were placed by him (in 1748) in the third order of his class Vermes under the name " Testacea," whilst the Echinoderms, Hydroids and Annelids, with the naked Mollusca, formed his second order termed " Zoophyta."

  • Ten years later he replaced the name " Zoophyta " by " Mollusca," which was thus in the first instance applied, not to the Mollusca at present so termed, but to a group consisting chiefly of other organisms. Gradually, however, the term Mollusca became used to include those Mollusca formerly placed among the " Testacea," as well as the naked Mollusca.

  • It is important to observe that the term µaXaiaa, of which Mollusca is merely a latinized form, was used by Aristotle to indicate a group consisting of the cuttle-fishes only.

  • As now classified, the Mollusca consist of the following subdivisions: - Grade A.

  • The definite erection of the Mollusca into the position of one of the great primary groups of the animal kingdom is due to George Cuvier (1788-1800), who largely occupied himself with the dissection of representatives of this type.

  • 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.

  • The main limitations of the sub-kingdom or phylum Mollusca, as laid down by Cuvier, and the chief divisions thus recognized within its limits by him, hold good to the present day.

  • At the same time, three of the classes considered by him as Mollusca have been one by one removed from that association in consequence of improved knowledge, and one additional class, incorporated since his day with the Mollusca with general approval, has, after more than forty years, been again detached and assigned an independent position owing to newly acquired knowledge.

  • The first of Cuvier's classes to be removed from the Mollusca was that of the Cirrhopoda.

  • Mollusca was that of the Nuda, better known as Tunicata.

  • In 1866 the Russian embryologist Kowalewsky startled the zoological world with a minute account of the developmental changes of Ascidia, one of the Tunicata, 5 and it became evident that the affinities of that class were with the Vertebrata, whilst their structural agreements with Mollusca were only superficial.

  • The last class which has been removed from the Cuvierian Mollusca is that of the Lamp-shells or Brachiopoda.

  • the Polyzoa or Bryozoa, which has been both added to and again removed from the Mollusca between Cuvier's date and the present day.

  • 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.

  • 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).

  • As thus purified by successive advances of embryological research, the Mollusca were reduced to the Cuvierian classes of Cephalopoda, Pteropoda, Gastropoda and Acephala.

  • In England, Owen's anatomy of the pearly nautilus,14 Huxley's discussion of the general morphology of the Mollusca,17 and Lankester's embryological investigations, 19 have aided in advancing our knowledge of the group. Two remarkable works of a systematic character dealing with the Mollusca deserve mention here - the Manual of the Mollusca, by Dr S.

  • " Mollusca "; 1883) was as follows: Of the four Cuvierian classes mentioned above, the Pteropoda were united with the Cephalopoda, on account of the apparent similarity of the cephalic tentacles in some of the former to the arms of the latter.

  • was published important advances have been made in our knowledge of the Mollusca, as the result of researches largely due to the interest excited in the subject by Lankester's article.

  • The most important and extensive contributions to this progress have been made by the Belgian zoologist, Dr Paul Pelseneer, who has made the Mollusca his special study.

  • The Lamellibranchia are no longer regarded as a distinct branch in contrast to the remaining Mollusca; according to Pelseneer they are allied to the Gastropoda and Scaphopoda, all three classes being derived from a common hypothetical ancestor, called Prorhipidoglossum.

  • The structural features which the Mollusca do possess in common with other animals belonging to other great phyla of the animal kingdom are those characteristic of the Coelomata, one of the two great grades (the other and lower being that of the Coelentera) into which the higher animals; or Metazoa as distinguished from the Protozoa, are divided.

  • The Mollusca agree in being coelomate with the phyla Vertebrata, Platyhelmia (flat-worms), Echinoderma, Appendiculata (insects, ringed-worms, &c.), and others - in fact, with all the Metazoa except the sponges, corals, polyps, and medusae.

  • In common with all other Coelomata, the Mollusca are at one period of life possessed of a prostomium or region in front of the mouth, which is the essential portion of the " head," and is connected with the property of forward locomotion in a definite direction and the steady carriage of the body (as opposed to rotation of the body on its long axis).

  • As a result, the Coelomata, and with them the Mollusca, present (in the first instance) the general condition of body known as bilateral symmetry; the dorsal is differentiated from the ventral surface, whilst a right and a left side similar to, or rather the complements of, one another are permanently established.

  • In common with all other Coelomata, the Mollusca have the mouth and first part of the alimentary canal which leads into the met-enteron formed by a special invagination of the outer layer of the primitive body-wall, not to be confounded with that which often, but not always, accompanies the antecedent formation of the archenteron; this invagination is termed the stomodaeum.

  • Such organs are absent in Mollusca in the adult state, but a pair of nephridia usually occurs in the larva.

  • In Mollusca the coelom is reduced and consists of two parts, the pericardial cavity which surrounds the heart, and the cavity of the gonads or generative organs.

  • In the majority of Mollusca the gonads are provided with a pair of ducts of their own.

  • This fact gives rise to the question whether the Mollusca are to be regarded as primitively segmented animals or not.

  • The structure of the Mollusca in the greater number of cases agrees with the hypothesis that the primitive form was unsegmented, and therefore had but one pair of coelomic ducts and one pair of nephridia.

  • Palaeontology therefore throws no light on the question whether the metameric or the unsegmented Mollusca were the earlier.

  • On the whole, then, the most probable conclusion is that the original ancestral form of the Mollusca was unsegmented, possessed one pair of true nephridia, and one pair of coelomic ducts whose function was to conduct the generative products to the exterior.

  • The chief types of Mollusca were already differentiated at the beginning of the geological record, and the metamerism which occurs in the Cephalopoda has been evolved within the limits of that class.

  • The characteristic organs of Mollusca are the mantle and shell, the foot, the ctenidia and the radula, of which all but the last are external.

  • - Ctenidia of various Mollusca (original).

  • z) are the branchial organs of the Mollusca.

  • In primitive Mollusca the mouth and anus are the two extremities of the body, but the anus may be brought to an anterior position by a ventral flexure, complicated in Gastropoda by a lateral torsion.

  • throughout the Mollusca.

  • The veliger, as soon as its shell has attained some extent and begins to assume definite shape, is no longer of a form common to Mollusca generally, but acquires characters peculiar to the partiY cular class to which its parents belong.

  • - " Veliger " embryonic form of Mollusca.

  • Mollusca, and it is possible to construct a diagrammatic mollusc, as was first done by Lankester, which will possess these primitive features.

  • (16) P. Geddes, " On the Mechanism of the Odontophore in certain Mollusca."

  • Huxley, " On the Morphology of the Cephalous Mollusca," Phil.

  • Lankester, " Contributions to the Developmental History of the Mollusca," Phil.

  • (1875); " Note on the Coelom and Vascular System of Mollusca and Arthropoda," Quart.

  • (1899); " Mollusca," Lankester's Treatise on Zoology, pt.

  • (24) Simroth, " Mollusca," Bronn's Klassen and Ordnungen des Thierreichs, Bd.

  • (26) Woodward, A Manual of the Mollusca (1880).

  • This Trochosphere is the characteristic larva of Mollusca, Annelida T OT (After Abbott, T5ky5 Zool.

  • The argument has come to rest on the agreement between the cell-lineage of Polyclads and that of certain Mollusca and Annelids.

  • CHITON, the name 1 given to fairly common littoral animals of rather small size which belong to the phylum Mollusca, and, in the possession of a radula in the buccal cavity, resemble more especially the Gastropoda.

  • Hubrecht in 1881 of a typical molluscan radula and odontophore in a new genus Proneomenia, allied to Neomenia, showed that the whole group belonged to the Mollusca.

  • Paul Pelseneer (1906) raised the group to the rank of a class of Mollusca, under von Jhering's name Amphineura.

  • (3) ix., 1901; P. Pelseneer, "Mollusca," Treatise on Zoology, edited by E.

  • Ray Lankester, "Mollusca," in the 9th ed.

  • Pelecypods among the true mollusca were increasing in numbers and importance (Aviculopecten, Posidonomya); Nucula, Carbonicola, Edmondia, Conocardium, Modiola, Gasteropods also were numerous (Murchisonia, Euomphalus, Naticopsis).

  • The inhabitants of the waters of this geographical phase include mollusca, which are supposed to have lived in brackish or fresh water, such as Anthracomya, Naiadites, Carbonicola, and many forms of Crustacea, e.g.

  • The plant-life of the Carboniferous was exceedingly luxuriant and varied, and the system is rich also in fossils of fishes, crustaceans, mollusca, insects and other forms of animal life.

  • p. 146.) The food of the flamingo seems to consist chiefly of small aquatic invertebrate animals whch live in the mud of lagoons, for instance Mollusca, but also of Confervae and other low salt-water algae.

  • Each of the principal groups of true mollusca was represented: Pelecypods (Modioloides); Gasteropods (Scenella, Pleurotomaria, Trochonema); Pteropods (Hyolithellus, Hyo- tithes, Salterella); Cephalopods (Orthoceras, Cystoceras).

  • Such places are frequented by numerous flocks of aquatic birds, which resort thither in search of fish and mollusca.

  • The muscular projection of the ventral surface called the foot, whose various modifications characterize the different classes of Mollusca, is almost entirely aborted.

  • They are distributed thus: Vertebrata, 8 species; Insecta, 17; Arachnida, 12; Myriapoda, 2; Crustacea, 5; Vermes, 3; Mollusca, 1.

  • Among the Jurassic Mollusca, also, are many species that are common in Europe.

  • SCAPHOPODA, the third of the five classes into which the Phylum Mollusca is divided.'

  • It is remarkable that in Scaphopoda only among Mollusca the blood-spaces are in communication with the external medium: a pair of apertures near the renal openings lead from the perianal sinus to the exterior and allow the blood to escape during violent contractions of the body.

  • In the Dentaliidae the mouth is surrounded by eight small lobes, but these are absent in the 1 For a discussion of its relationship to the other classes of the Phylum see Mollusca.

  • (1904); Paul Pelseneer, Mollusca; Lankester's Treatise on Zoology, pt.

  • Acasta sulcata, Lamk., in the scientific study of zoology had replaced the fabulous tales of medieval writers, it was a long time before the true affinities of the barnacles were appreciated, and they were at first classed with the Mollusca, some of which they closely resemble in external appearance.

  • His earlier publications were on zoology; he dealt with the Amphibia (1839), Reptiles (1840), with Mollusca and Crustacea (1845) and more generally with the invertebrate fauna of the Mediterranean (1854).

  • The skeletons of many other organisms, such as Polyzoa and Mollusca, contribute to coral masses but cannot be included in the term "coral."

  • Anatomic, Berlin, 1845) as that of a primary division of animals, the others recognized in that treatise being Protozoa, Zoophyta, Vermes, Mollusca and Vertebrata.

  • Fishes, of an Indo-Malay type, are numerous and varied; Mollusca, especially marine, and Crustaceae are also very numerous.

  • 140 species,' belonging to the Mollusca, Foraminifera, Echinodermata, Actinozoa and Plantae; but the researches of French geologists made the total number of Madagascar fossils known in 1907 to be not fewer than 280 species.

  • Linnaeus applied the Latin term Vermes to the modern zoological divisions Mollusca, Coelentera, Protozoa, Tunicata, Echinoderma (qq.v.), as well as to those forms which more modern zoologists have recognized as worms. As a matter of convenience the term Vermes or Vermidea is still employed, for instance in the International Catalogue of Zoological Literature and the Zoological Record, to cover a number of wormlike animals.

  • Guilding, "Mollusca caribbaeana: an account of a new genus of Mollusca," Zool.

  • This lignite and the accompanying leaf-bearing clays underlie and are apparently older than the strata with Newer Pliocene mammals and mollusca.

  • The mollusca Section at NMW, Cardiff holds one of the largest mollusk collections in Europe.

  • In zoology, the mollusca are divided into cephalous and acephalous (Acephala), according as they have or have not an organized part of their anatomy as the seat of the brain and special senses.

  • Turtle and sea-snakes abound, as do mollusca, of which a few are peculiar, and zoophytes.

  • GASTROPODA, the second of the five classes of animals constituting the phylum Mollusca.

  • For a discussion of the relationship of the Gastropoda to the remaining classes of the phylum, see MoLLUSCA.

  • It will be remembered that, according to Spengel, the osphradium of mollusca is definitely and intimately related to the gill-plume or ctenidium, being always placed near the base of that organ; further, Spengel has shown that the nerve-supply of this olfactory organ is always derived from the visceral loop. Accord ingly, the nerve-supply FIG.

  • time when the fact that the renal organ s,s', Nerves (right and of the Mollusca, as a rule, opens into the left) to the mantle.

  • The general structure of the Molluscan intestine has not been sufficiently investigated to render any comparison of this structure of Patella with that of other Mollusca possible.

  • Internally this glandular sac presents a second slit or aperture which leads into the pericardium (as is now found to be the case in all Mollusca).

  • The histology of the nervous system of Mollusca has yet to be seriously inquired into.

  • In other Pectinibranchia (and such variations are representative for all Mollusca, and not characteristic only of Pectinibranchia) we find that there is a very unequal division of the egg-cell at the commencement of embryonic development, as in Nassa.

  • The general features of this process and of the relation of the blastopore to mouth and anus have been explained in treating of the development of Mollusca generally.

  • This is the largest group of Mollusca, including nearly sixty families, some of which are insufficiently known from the anatomical point of view.

  • The Pteropoda, formerly regarded as a distinct class of the Mollusca, were interpreted by E.

  • Some Opisthobranchia are striking examples of degeneration (some Nudibranchia), having none of those regions or processes of the body developed which distinguish the archaic Mollusca from such flat-worms as the Dendrocoel Planarians.

  • In deed, were it not for their retention of the characteristic odontophore we should have little or no indication that such forms as Phyllirhoe and Limapontia really belong to the Mollusca at all.

  • Aplysia, like other Mollusca, develops a primitive shellsac in its trochosphere stage of development, which disappears and is succeeded by a nautiloid shell (fig.

  • In one genus (Planorbis) the plasma of the blood is coloured red by haemoglobin, this being the only instance of the presence of this body in the blood of Glossophorous Mollusca, though it occurs in corpuscles in the blood of the bivalves Arca and Solen (Lankester).

  • 60), at one time supposed to be the developing anus, but shown by Lankester to be identical with the " shell-gland " discovered by him in other Mollusca (Pisidium, Pleurobranchidium, Neritina, &c.).

  • Whether the closed primitive shell-sac of the slugs (and with it the transient embryonic shell-gland of all other Mollusca) is precisely the same thing as the closed sac in which the calcareous pen or shell of the Cephalopod Sepia and its allies is formed, is a further question which we shall consider when dealing with the Cephalopoda.

  • In most other Mollusca (Anisopleurous Gastropods, Pteropods and Conchifera) there is a want of such continuity; the primitive shell-sac contributes no factor to the permanent shell, or only a very minute FIG.

  • (After Spengel.) being formed afresh on the surface of the visceral hump. It is, then, in this sense that we may speak of primary, secondary and tertiary shells in Mollusca, recognizing the fact that they may be merely phases fused by continuity of growth so as to form but one shell, or that in other cases they may be presented to us as separate individual things, in virtue of the non-development of the later phases, or in virtue of sudden changes in the activity of the mantle-surface causing the shedding FIG.

  • Herdman, " On the Structure and Functions of the Cerata or Dorsal Papillae in some Nudibranchiate Mollusca," Quart.

  • P. Woodward, Manual of the Mollusca (2nd ed., with appendix, London, 1869); E.

  • Hanley, History of British Mollusca (4 vols., London, 1853) Alder and Hancock, Monograph of British Nudibranchiate Mollusca (London, Roy.

  • Society, 1845); P. Pelseneer, Mollusca.

  • Ray Lankester, " Mollusca," in 9th ed.

  • - Diagrams of the five classes of Mollusca, from the left side.

  • A history of the British forms is given in Gwyn Jeffreys's British Conchology (1862), and by Forbes and Hanley in British Mollusca.

  • For speciegraphical details, see Woodward's Manual of the Mollusca (1875), and Bronn's Tierreich (Weichtiere).

  • Numerous raised beaches and terraces, containing shells of marine mollusca, &c., occur along the whole coast of Greenland, and indicate that the whole of this large island has been raised, or the sea has sunk, in post-glacial times, after the inland ice covered its now icebare outskirts.

  • " Conchiolin," the matrix of shells of the mollusca, is only slightly soluble in acids.

  • Brachiopods have been at various times placed with the Mollusca, the Chaetopoda, the Chaetognatha, the Phoronidea, the Polyzoa, the Hemichordata, and the Urochordata.

  • Associated with Ray in his work, and more especially occupied with the study of the Worms and Mollusca, was Martin Lister (1638-1712), celebrated also as the author of the first geological map.

  • Animalia Mollusca.

  • He upset (1830) Cuvier's retention of the Cirripedes among Mollusca, and his subsequent treatment of them as an isolated class, by showing that they begin life as free-swimming Crustacea identical with the young forms of other Crustacea.

  • Malaeozoaria or Mollusca.

  • Mollusca proper.

  • Mollusca (q.v.).

  • These Trematodes occur in the alimentary canal and adjacent organs of Mollusca, the gall-bladder of Chimaera, and the intestine of Chelonia and of certain fish.

  • This appears to indicate B that the Polyzoa are remotely allied to other phyla in which this type of larva prevails, and in particular to the Mollusca and Chaetopoda, as well as to the Rotifera, which are regarded as persistent Trochospheres.

  • These, like the mollusca, indicate the influence of the Kuro Shiwo and the south-west monsoon, for they have close affinity with species found in the Indian and Pacific Oceans.

  • Malta has several species of zoophytes, sponges, mollusca and crustacea.

  • de Pourtales pointed out in 1870; they consist of remains of deep-sea corals, serpulae, echinoderms and mollusca united Sands, gravels, muds, &c.

  • Murray and Renard define globigerina ooze as containing at least 30% of calcium carbonate, in which the remains of pelagic (not benthonic) foraminifera predominate and in which remains of pelagic mollusca such as pteropods and heteropods, ostracodes and also coccoliths (minute calcareous algae) may also occur.

  • The phosphate beds contain Eocene fossils derived from the underlying strata and many fragments of Pleistocene vertebrata such as mastodon, elephant, stag, horse, pig, &c. The phosphate occurs as lumps varying greatly in size, scattered through a sand or clay; they often contain phosphatized Eocene fossils (Mollusca, &c.).

  • He was also author (with John Lycett) of A Monograph of the Mollusca from the Great Oolite (Palaeontographical Soc., 1850-1853).

  • 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.

  • In the latter respect, and in the fact that they frequently develop by a metamorphosis, they approach the Mollusca, but they differ from that group notably in the occurrence of metameric segmentation affecting many of the systems of organs.

  • 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.

  • Ope yxta, gills), the fourth of the five classes of animals constituting the phylum Mollusca.

  • It, as in other Mollusca, is not a blood-space but develops from the coelom, and it communicates with the exterior by the pair of renal tubes.

  • As in Cephalopoda (and possibly other Mollusca) water can be introduced through the nephridia into this space.

  • They are totally distinct from the cephalic eyes of typical Mollusca, and have a different structure and historical development.

  • 21), so that its fibres join the anterior faces of the nerve-end cells as in Vertebrates, instead of their posterior faces as in the cephalic eyes of Mollusca and Arthropoda; moreover, the lens is not a cuticular product but a cellular structure, which, again, is a feature of agreement with the Vertebrate FIG.

  • Peck, " The Minute Structure of the Gills of Lamellibranch Mollusca," Quart.

  • iii.; Paul Pelseneer, " Mollusca," Treatise on Zoology, edited by E.

  • MOLLUSCA, one of the great " phyla," or sub-kingdoms, of the animal pedigree or kingdom.

  • The shell-bearing forms belonging to this group which were known to Linnaeus were placed by him (in 1748) in the third order of his class Vermes under the name " Testacea," whilst the Echinoderms, Hydroids and Annelids, with the naked Mollusca, formed his second order termed " Zoophyta."

  • Ten years later he replaced the name " Zoophyta " by " Mollusca," which was thus in the first instance applied, not to the Mollusca at present so termed, but to a group consisting chiefly of other organisms. Gradually, however, the term Mollusca became used to include those Mollusca formerly placed among the " Testacea," as well as the naked Mollusca.

  • It is important to observe that the term µaXaiaa, of which Mollusca is merely a latinized form, was used by Aristotle to indicate a group consisting of the cuttle-fishes only.

  • As now classified, the Mollusca consist of the following subdivisions: - Grade A.

  • The definite erection of the Mollusca into the position of one of the great primary groups of the animal kingdom is due to George Cuvier (1788-1800), who largely occupied himself with the dissection of representatives of this type.

  • 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.

  • The main limitations of the sub-kingdom or phylum Mollusca, as laid down by Cuvier, and the chief divisions thus recognized within its limits by him, hold good to the present day.

  • At the same time, three of the classes considered by him as Mollusca have been one by one removed from that association in consequence of improved knowledge, and one additional class, incorporated since his day with the Mollusca with general approval, has, after more than forty years, been again detached and assigned an independent position owing to newly acquired knowledge.

  • The first of Cuvier's classes to be removed from the Mollusca was that of the Cirrhopoda.

  • Mollusca was that of the Nuda, better known as Tunicata.

  • In 1866 the Russian embryologist Kowalewsky startled the zoological world with a minute account of the developmental changes of Ascidia, one of the Tunicata, 5 and it became evident that the affinities of that class were with the Vertebrata, whilst their structural agreements with Mollusca were only superficial.

  • The last class which has been removed from the Cuvierian Mollusca is that of the Lamp-shells or Brachiopoda.

  • the Polyzoa or Bryozoa, which has been both added to and again removed from the Mollusca between Cuvier's date and the present day.

  • 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.

  • 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).

  • As thus purified by successive advances of embryological research, the Mollusca were reduced to the Cuvierian classes of Cephalopoda, Pteropoda, Gastropoda and Acephala.

  • In England, Owen's anatomy of the pearly nautilus,14 Huxley's discussion of the general morphology of the Mollusca,17 and Lankester's embryological investigations, 19 have aided in advancing our knowledge of the group. Two remarkable works of a systematic character dealing with the Mollusca deserve mention here - the Manual of the Mollusca, by Dr S.

  • " Mollusca "; 1883) was as follows: Of the four Cuvierian classes mentioned above, the Pteropoda were united with the Cephalopoda, on account of the apparent similarity of the cephalic tentacles in some of the former to the arms of the latter.

  • was published important advances have been made in our knowledge of the Mollusca, as the result of researches largely due to the interest excited in the subject by Lankester's article.

  • The most important and extensive contributions to this progress have been made by the Belgian zoologist, Dr Paul Pelseneer, who has made the Mollusca his special study.

  • The Lamellibranchia are no longer regarded as a distinct branch in contrast to the remaining Mollusca; according to Pelseneer they are allied to the Gastropoda and Scaphopoda, all three classes being derived from a common hypothetical ancestor, called Prorhipidoglossum.

  • The structural features which the Mollusca do possess in common with other animals belonging to other great phyla of the animal kingdom are those characteristic of the Coelomata, one of the two great grades (the other and lower being that of the Coelentera) into which the higher animals; or Metazoa as distinguished from the Protozoa, are divided.

  • The Mollusca agree in being coelomate with the phyla Vertebrata, Platyhelmia (flat-worms), Echinoderma, Appendiculata (insects, ringed-worms, &c.), and others - in fact, with all the Metazoa except the sponges, corals, polyps, and medusae.

  • In common with all other Coelomata, the Mollusca are at one period of life possessed of a prostomium or region in front of the mouth, which is the essential portion of the " head," and is connected with the property of forward locomotion in a definite direction and the steady carriage of the body (as opposed to rotation of the body on its long axis).

  • As a result, the Coelomata, and with them the Mollusca, present (in the first instance) the general condition of body known as bilateral symmetry; the dorsal is differentiated from the ventral surface, whilst a right and a left side similar to, or rather the complements of, one another are permanently established.

  • In common with all other Coelomata, the Mollusca have the mouth and first part of the alimentary canal which leads into the met-enteron formed by a special invagination of the outer layer of the primitive body-wall, not to be confounded with that which often, but not always, accompanies the antecedent formation of the archenteron; this invagination is termed the stomodaeum.

  • Such organs are absent in Mollusca in the adult state, but a pair of nephridia usually occurs in the larva.

  • In Mollusca the coelom is reduced and consists of two parts, the pericardial cavity which surrounds the heart, and the cavity of the gonads or generative organs.

  • In the majority of Mollusca the gonads are provided with a pair of ducts of their own.

  • This fact gives rise to the question whether the Mollusca are to be regarded as primitively segmented animals or not.

  • The structure of the Mollusca in the greater number of cases agrees with the hypothesis that the primitive form was unsegmented, and therefore had but one pair of coelomic ducts and one pair of nephridia.

  • Palaeontology therefore throws no light on the question whether the metameric or the unsegmented Mollusca were the earlier.

  • On the whole, then, the most probable conclusion is that the original ancestral form of the Mollusca was unsegmented, possessed one pair of true nephridia, and one pair of coelomic ducts whose function was to conduct the generative products to the exterior.

  • The chief types of Mollusca were already differentiated at the beginning of the geological record, and the metamerism which occurs in the Cephalopoda has been evolved within the limits of that class.

  • The characteristic organs of Mollusca are the mantle and shell, the foot, the ctenidia and the radula, of which all but the last are external.

  • - Ctenidia of various Mollusca (original).

  • z) are the branchial organs of the Mollusca.

  • In primitive Mollusca the mouth and anus are the two extremities of the body, but the anus may be brought to an anterior position by a ventral flexure, complicated in Gastropoda by a lateral torsion.

  • The egg-cell of Mollusca is either free from food-material - a simple protoplasmic corpuscle or charged with food-material to a greater or less extent.

  • which adhere to a procedure which was probably common at one time to all then existing Mollusca and has been departed from only in later and special lines of descent - show approximately the following history.

  • throughout the Mollusca.

  • The veliger, as soon as its shell has attained some extent and begins to assume definite shape, is no longer of a form common to Mollusca generally, but acquires characters peculiar to the partiY cular class to which its parents belong.

  • - " Veliger " embryonic form of Mollusca.

  • Mollusca, and it is possible to construct a diagrammatic mollusc, as was first done by Lankester, which will possess these primitive features.

  • (16) P. Geddes, " On the Mechanism of the Odontophore in certain Mollusca."

  • Huxley, " On the Morphology of the Cephalous Mollusca," Phil.

  • Lankester, " Contributions to the Developmental History of the Mollusca," Phil.

  • (1875); " Note on the Coelom and Vascular System of Mollusca and Arthropoda," Quart.

  • (1899); " Mollusca," Lankester's Treatise on Zoology, pt.

  • (24) Simroth, " Mollusca," Bronn's Klassen and Ordnungen des Thierreichs, Bd.

  • (26) Woodward, A Manual of the Mollusca (1880).

  • This Trochosphere is the characteristic larva of Mollusca, Annelida T OT (After Abbott, T5ky5 Zool.

  • The argument has come to rest on the agreement between the cell-lineage of Polyclads and that of certain Mollusca and Annelids.

  • CHITON, the name 1 given to fairly common littoral animals of rather small size which belong to the phylum Mollusca, and, in the possession of a radula in the buccal cavity, resemble more especially the Gastropoda.

  • Hubrecht in 1881 of a typical molluscan radula and odontophore in a new genus Proneomenia, allied to Neomenia, showed that the whole group belonged to the Mollusca.

  • Paul Pelseneer (1906) raised the group to the rank of a class of Mollusca, under von Jhering's name Amphineura.

  • (3) ix., 1901; P. Pelseneer, "Mollusca," Treatise on Zoology, edited by E.

  • Ray Lankester, "Mollusca," in the 9th ed.

  • Pelecypods among the true mollusca were increasing in numbers and importance (Aviculopecten, Posidonomya); Nucula, Carbonicola, Edmondia, Conocardium, Modiola, Gasteropods also were numerous (Murchisonia, Euomphalus, Naticopsis).

  • The inhabitants of the waters of this geographical phase include mollusca, which are supposed to have lived in brackish or fresh water, such as Anthracomya, Naiadites, Carbonicola, and many forms of Crustacea, e.g.

  • The plant-life of the Carboniferous was exceedingly luxuriant and varied, and the system is rich also in fossils of fishes, crustaceans, mollusca, insects and other forms of animal life.

  • p. 146.) The food of the flamingo seems to consist chiefly of small aquatic invertebrate animals whch live in the mud of lagoons, for instance Mollusca, but also of Confervae and other low salt-water algae.

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