{"article":{"id":"britannica-11-pig-5","work_id":"britannica-11","title":"Pig. 5","normalized_title":"pig-5","slug":"pig-5","aliases":[],"subtitle":"Internet Archive OCR import","body_text":"PIG. 5. horizontal solenia unite to B. Diagrammatic longitudinal section of a corallite. showing two platforms. £,nd Simn,e anclcup-fhaped^bulae, ,. (After S. J. H,ckson.) their consists of loose spicules. In the Tubiporidae the spicules of the proximal part of the body-wall are fused together to form a firm tube, the corallite, into which the distal part of the zooid can be retracted. The corallites are connected at intervals by horizontal platforms containing solenia, and at the level of each platform the cavity of the corallite is divided by a transverse calcareous partition, either flat or cup-shaped, called a tabula. Formerly all corals in which tabulae are present were classed together as Tabulata, but Tubipora is an undoubted Alcyonarian with a lamellar stolon, and the structure of the fossil genus Syringopora, which has vertical corallites united by horizontal solenia, clearly shows its affinity to Tubipora. The Favositidae, a fossil, family from the Silurian and Devonian, have a massive corallum composed of numerous polygonal corallites closely packed together. The cavities of adjacent corallites communicate by means of numerous perforations, which appear to represent solenia, and numerous transverse tabulae are also present. In Faros it fs hemiiphaerico. a number of radial spines, projecting into the cavity FIG. 6.— Portion of a colony of Coral- of the corallite. give it the Hum rubrum. showing expanded and appearance of a madreporcontracted zooids. In the lower part of anan coral. the figure the cortex has been cut away In the o™cr ALCYONto show the axis, ax, and the longi- *CE* tne colony consists tudinal canals, U, surrounding it. of bunches of elongate cylindrical zooids, whose proximal portions are united by solenia and compacted, by fusion of their own walls and those of the solenia. into a fleshy mass called the coenenchyma. Thus the coenenchyma forms a stem, sometimes branched, from the surface of which the free portions of the zooids project. The skeleton of the Alcyonacea consists of separate calcareous spicules, which are often, especially in the Nephthyidae, so abundant and so closely interlocked as to form a tolerably firm and hard armour. The order comprises the families Xeniidae, Alcyonidat and Ncphlhyidae. Alcyonium digitatum, a pink digitate form popularly known as \" dead men's fingers,\" is common in 10-20 fathoms of water off the English coasts. In the order PSEUDAXOMA the colonies arc upright and branched, of a number of short zooid* whose proximal end* are imbedded in a coenenchyma containing numerou* ramifying tolrnia and iniculex. The coenenchyma i* further HirTrrrntiatra into a medullary ix>rt ion and a cortex. The latter contain* the proximal mi piftiii) of the zooid* and numerous but separate spicules. The meduMary portion is densely crowded with spiculea of different shape from those in the cortex, and in some forms the tpicule* are cemented together to form a hard supporting axis. There are four families of Pseudaxonia — the Briareidae, Sclerogorgidae, Melitodidae, and CoraUidae. In the first-named the medulla is penetrated by solenia and forms an indistinct axis; in the remainder the medulla is devoid of solenia, and in the Melitodidae and CoraUidae it forms a dense axis, which in the Melitodidae consists of alternate ca lea reousandhorny joints. The precious red coral of commerce, Corallium rubrum (fig. 6), a member of the family Corillidae, is found at depths varying FIG. 7.— The sea-fan (Gorgonia from 15 to 1 20 fathoms in cavolinif). the Mediterranean Sea, chiefly on the African coast. It owes its commercial value to the beauty of its hard red calcareous axis which in life is covered by a cortex in which the proximal moieties of the zooids are imbedded. Corallium rubrum has been the subject of a beautifully-illustrated memoir by de Lacaze-Duthiers, which should be consulted for details of anatomy. The AXIFERA comprise those corals that have a horny or calcified axis, which in position corresponds to the axis of the Pseudaxonia, but, unlike it, is never formed of fused spicules; the most familiar example is the pink sea-fan, Gorgonia cavolinii, which is found in abundance in 10-25 fathoms of water off the English coasts (fig. 7). In this order the axis is formed as an ingrowth of the ectoderm of the base of the mother zooid of the colony, the cavity of the ingrowth being filled by a horny substance secreted by the ectoderm. In Gorgonia the axis remains horny throughout life, but in many forms it is further strengthened by a deposit of calcareous matter. In the family Isidinae the axis consists of alternate segments of horny and calcareous substance, the latter being amorphous. The order contains six families — the Dasygorgtdae, Isidae, Primnoidae, Muriceidae, Plexauridae, and Gorgonidae. In the order STELECHOTOKEA the colony consists of a stem formed by a greatlyelongated mother zooid, and the daughter zooids are borne as lateral buds on the stem. In the section Aiiphonacea the colonies are upright and branched, springing from membranous or ramifying stolons. They resemble and are closely allied to certain families of the Cornulariidae, differing from them only in mode of budding and in the disposition of the daughter zooids FIG. 8. A, Colony of Pennatula phospkorea from the metarachidia! aspect, p. The peduncle. B, Section of the rachis bearing a single pinna, a. Axis; b, metarachiilial; c, prorachidial; d, pararachidial stem canals. round a central, much-elongated mother zooid. The section contains two families, the Trlrstidae and the Coelogorgidoe. The second section comprises the Pennotulocea or sea-pens, which are remarkable from the fact that the colony is not fixed by the base to a rock or other","body_html":"

PIG. 5. horizontal solenia unite to B. Diagrammatic longitudinal section of a corallite. showing two platforms. £,nd Simn,e anclcup-fhaped^bulae, ,. (After S. J. H,ckson.) their consists of loose spicules. In the Tubiporidae the spicules of the proximal part of the body-wall are fused together to form a firm tube, the corallite, into which the distal part of the zooid can be retracted. The corallites are connected at intervals by horizontal platforms containing solenia, and at the level of each platform the cavity of the corallite is divided by a transverse calcareous partition, either flat or cup-shaped, called a tabula. Formerly all corals in which tabulae are present were classed together as Tabulata, but Tubipora is an undoubted Alcyonarian with a lamellar stolon, and the structure of the fossil genus Syringopora, which has vertical corallites united by horizontal solenia, clearly shows its affinity to Tubipora. The Favositidae, a fossil, family from the Silurian and Devonian, have a massive corallum composed of numerous polygonal corallites closely packed together.

\n

The cavities of adjacent corallites communicate by means of numerous perforations, which appear to represent solenia, and numerous transverse tabulae are also present. In Faros it fs hemiiphaerico. a number of radial spines, projecting into the cavity FIG. 6.— Portion of a colony of Coral- of the corallite. give it the Hum rubrum. showing expanded and appearance of a madreporcontracted zooids. In the lower part of anan coral. the figure the cortex has been cut away In the o™cr ALCYONto show the axis, ax, and the longi- *CE* tne colony consists tudinal canals, U, surrounding it. of bunches of elongate cylindrical zooids, whose proximal portions are united by solenia and compacted, by fusion of their own walls and those of the solenia. into a fleshy mass called the coenenchyma. Thus the coenenchyma forms a stem, sometimes branched, from the surface of which the free portions of the zooids project. The skeleton of the Alcyonacea consists of separate calcareous spicules, which are often, especially in the Nephthyidae, so abundant and so closely interlocked as to form a tolerably firm and hard armour. The order comprises the families Xeniidae, Alcyonidat and Ncphlhyidae.

\n

Alcyonium digitatum, a pink digitate form popularly known as " dead men's fingers," is common in 10-20 fathoms of water off the English coasts. In the order PSEUDAXOMA the colonies arc upright and branched, of a number of short zooid* whose proximal end* are imbedded in a coenenchyma containing numerou* ramifying tolrnia and iniculex. The coenenchyma i* further HirTrrrntiatra into a medullary ix>rt ion and a cortex. The latter contain* the proximal mi piftiii) of the zooid* and numerous but separate spicules. The meduMary portion is densely crowded with spiculea of different shape from those in the cortex, and in some forms the tpicule* are cemented together to form a hard supporting axis. There are four families of Pseudaxonia — the Briareidae, Sclerogorgidae, Melitodidae, and CoraUidae. In the first-named the medulla is penetrated by solenia and forms an indistinct axis; in the remainder the medulla is devoid of solenia, and in the Melitodidae and CoraUidae it forms a dense axis, which in the Melitodidae consists of alternate ca lea reousandhorny joints. The precious red coral of commerce, Corallium rubrum (fig. 6), a member of the family Corillidae, is found at depths varying FIG.

\n

7.— The sea-fan (Gorgonia from 15 to 1 20 fathoms in cavolinif). the Mediterranean Sea, chiefly on the African coast. It owes its commercial value to the beauty of its hard red calcareous axis which in life is covered by a cortex in which the proximal moieties of the zooids are imbedded. Corallium rubrum has been the subject of a beautifully-illustrated memoir by de Lacaze-Duthiers, which should be consulted for details of anatomy. The AXIFERA comprise those corals that have a horny or calcified axis, which in position corresponds to the axis of the Pseudaxonia, but, unlike it, is never formed of fused spicules; the most familiar example is the pink sea-fan, Gorgonia cavolinii, which is found in abundance in 10-25 fathoms of water off the English coasts (fig. 7). In this order the axis is formed as an ingrowth of the ectoderm of the base of the mother zooid of the colony, the cavity of the ingrowth being filled by a horny substance secreted by the ectoderm. In Gorgonia the axis remains horny throughout life, but in many forms it is further strengthened by a deposit of calcareous matter. In the family Isidinae the axis consists of alternate segments of horny and calcareous substance, the latter being amorphous.

\n

The order contains six families — the Dasygorgtdae, Isidae, Primnoidae, Muriceidae, Plexauridae, and Gorgonidae. In the order STELECHOTOKEA the colony consists of a stem formed by a greatlyelongated mother zooid, and the daughter zooids are borne as lateral buds on the stem. In the section Aiiphonacea the colonies are upright and branched, springing from membranous or ramifying stolons. They resemble and are closely allied to certain families of the Cornulariidae, differing from them only in mode of budding and in the disposition of the daughter zooids FIG. 8. A, Colony of Pennatula phospkorea from the metarachidia! aspect, p. The peduncle. B, Section of the rachis bearing a single pinna, a. Axis; b, metarachiilial; c, prorachidial; d, pararachidial stem canals. round a central, much-elongated mother zooid. The section contains two families, the Trlrstidae and the Coelogorgidoe. The second section comprises the Pennotulocea or sea-pens, which are remarkable from the fact that the colony is not fixed by the base to a rock or other

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