Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/406

Rh 370 CORALS Sometimes the coraUites are simply in contact with one another, or their walls may be fused together, in which case there is a great tendency for the calices to become polygonal by mutual pressure. In other cases, again, the corallites are united together by the great development and coalescence of the costse. The Zoantharia sclerodermata were divided by Milne- Edwards and Jules Haime into the four great sections of the Aporosa, Perforate, Tabulata, and Tubulosa. The first two of these groups constitute large, important, and natural divisions, whilst the two latter are of doubtful affinities and uncertain value. (1.) The APOROSA are characterized by the fact that the calcareous tissue of the corallum is more or less compact and imperforate ; the eepta are well developed, and usually constitute complete lam ellae ; while the walls are generally quite complete, and, as a rule, are not pierced by any apertures. Dissepiments or synapti- culse are usually present, but tabulae are rarely developed. This section includes the most highly developed of existing corals, and it is subdivided by Milne-Edwards and Haime into six families: a. Turbinolidx. Corallum simple or compound, but never possessing a ccenenchyma; septa well developed, usually regularly granulated on the two sides, but their free edges not denticulated ; interseptal loculi open and free from dissepiments or synapticulae ; costse well marked and straight; wall im perforate. The principal genera of this family are Bathycyathus, Brachycyalhus, Trochocyathi/s, Leptocyalhus, Thecocyathus, Dtscocyalhus, Cyclocyathus, Para- tyathus, Deltocyathtts, P/acocyalhus, Turbinoha, Sphenotrochus, Platytrochus, Ceratotrochits, Discotrochus, Placotrochus, lilastotrochus, Rhizotrochus, Onchotrochus, Desmophyllum, and f label lum. b. Pseiuloturbmohdx. Corallum simple, resembling that of the preceding in most respects, but having the septa composed of three laminae each, which are free internally, but are united externally by a single costa. The only genus of this group is the extinct Dasmia. c. Ocultnidx.Corallnm compound; ccenenchyma abundant, compact, its surface smooth or striated, but not echinulate; walls imperforate, the lower part of the corallites becoming filled up in advancing age; dissepiments scanty ; no synapticulae; occasionally tabulae. The principal genera of this family are Ocuhna, Cyathohelia, AstroheHa, Synhetia, Lophohelia, Amphihelia, Diplohelia, Axohelia, Cryptoheha, Endvheha, Stylaster, Styhphora, Dendracis, Orbtcella, Pocillopora, and Seriatopora (!) d. Astrxidx. Corallum simple or compound, usually increasing by fission; walls perfect and Imperforate; ccenenchyma absent, or if present lax; inter septal dissepiments abundantly developed, no synapticulss nor tabulae. The principal genera of this family are PlacosmiHa, TrochosmHia, Parasmi/ia, Eusmilia, TfiecosmiHa, Barysmilia, Diploctenium, Montlivaltia, Dendrogyra, Rhipidogyra, Pachygyra, StyHna, A&amp;gt;troc&amp;lt;xnia, Stephanocoenia, Phyllocoema, Dichoccenia, Heteroc&nia, Sarcinula, Caryophyllia, LobophyHia, Rhabdophyllta, (Xadophyllia. Symphyllia, Oulophyl/ta, Calamophyllia, Eunomia, Latimeandra, Hfeandrma, Dip orta. Leptoria, Manicina. Cladocora, Favia, Ooniocora, Mussa, Pleurocoi-a, Astrxa, Oulastnea, Leplastrxa, Solenastrxa, Pnonastrxa, Sider- astrxa, Septastrxa, Isaslrxa, Synastrxa, Thamnastrxa, Goniastrxa, Astroides, Angia, Cryptangia, Rhizangia, Astrattgia, Phyllangw, Oulangia, Echtnopora, Eattersbyia, and Heteropliyllia. e. Pseudofungidx Corallum compound, the basal plate or wall perforated (as in the Fungidx), but the corallites without synapticulas and with interseptal dissepiments (as in the Astrxidx). The only genus of this family is Aferulma. /. Fungidx. Corallum simple or compound, usually discoidal or laminar; the calice shallow and open at its sides in the simple forms, confluent and not cir cumscribed in the compound forms, septa complete, coalescent with the costa:, imperforate, their edges dentate, and their sides echinulate or furnisljed with synapticulae ; wall basal, generally perforated; no dissepiments, nor tabuloa. The chief genera of this family are Cyclolitei, Fungia, Ctenactis, Micra- bacia, Anabacia, Cryptobacia, Cycloseris, Trochoseris, Cyathoseris, Comoseris, Protoseris, Lophoseris, Agaricia, Pachyseris, Leptoseris, and Phyllastrxa. (2.) The PEKFORATA are distinguished by the fact that the calcareous tissue of the corallum is more or less porous, loosely aggregated, spongy, or reticulate, the walls in all being perforated with more or fewer apertures. The septa are generally well de veloped, but may be represented only by trabeculse. The visceral chamber is usually more or less completely open from top to bottom, but there may be imperfect dissepiments, and in some cases well-developed tabulae are present. The section Perforata comprises the following families :- a. Euptammida.ConHvm simple or compound; septa well developed, lamellar, for the most part perforated; a spongy columella is present; walls perforated, granular, sub-costulate, often thickened with age. Septa numerous, those of the last cycle bent towards those of the penultimate cycle, so as to pro duce the appearance of a six or twelve-branched star; interseptal loculi open, or only with a few dissepiments ; costas rudimentary. The chief genera of this family are Eupsammia Endopachys, BalarwphylHa, Heteropsammia, Lobopsammia, Cotnopsammia, Stereopsammia, Slephanophy! lia, and Dendrophyllia. t&amp;gt; Afadreporidx.Cora.lum compound, increasing by gem-nation; ccenen chyma abundant, spongy, and reticulate; walls porous, not distinct from the coenenchyma; septa often well developed; nosynapticul.-c, and, generally speak ing, no dissepiments, but occasionally tabulae. (The diagnosis of this family may require amendment for the reception of the Favositidx proper) The chief genera of this family are Madrepora, Explanaria, Astr seopora, Turbinaria, Palxacis, Alreopora, Furositopora, and Co 1. umnopora (?) c. Poritidx. Corallum wholly composed of reticulate sclerenchyma; septa well developed, but only composed of styliform processes, which by their junction form a kind of irregular lattice-work. Walls reticulate, not distinct from tha sclerenchyma; a few dissepiments, but no tabula;. The principal genera of this family are Porites, Lithat xa, Coscinarxa, Rliodarxa, Porarxa, Protarxa, Microso- lena, Gontopora, Monttpora, and Psammocora. (3. ) The TABULATA constitute a group founded by Milne-Edwards and Haime for the reception of a number of corals essentially char acterized by the rudimentary condition or absence of septa, con joined with the presence of well-developed tabulae dividing the visceral chamber into so many distinct stories. Hecent researches, however, by Agassiz, Verrill, Lindstrom, Duncan, Dollfus, Moseley, and others, have clearly shown that the old order Tabulata is a heterogeneous assemblage, comprising forms of very different zoolo gical affinities, and that it must be broken up and redistributed, or greatly restricted. It has been unequivocally shown, in fact, that the presence of tabuhe cannot, of itself, be regarded as a point of high classificatory value, since these structures occur in forms in other respects no way related to each other. Thus, tnbuhe occur in Pocillopora, Cyathophora, and occasionally in Lopho/iclia amongst the Aporosa, in Alvcopora and Favositopora amongst the Perforata, in Hcliopora amongst the Alcyonaria, in the great majority of the Rugosa, and in certain of the Polyzoa (e. g., Eadiopora and Heterodictya). It has also been shown that some of the so-called &quot; tabulate corals&quot; are not Actinozoa at ail, but that they belong to the Molluscan order of the Polyzoa; and good authorities believe that this is the true position of a very large number of the forms previously in cluded under this head. The whole of this subject is at pre sent under investigation, and the ultimate results of the inquiry are uncertain. It will, therefore, be sufficient here to indicate the views which are now generally entertained as to the true affinities of the principal forms included by Milne-Edwards and Haimo amongst the Tabulata. FIG. 7. &quot;Tabulate &quot; Corals. A, Portion of the corallum of Favosites favosa, Goldfuss, of the natural size. B, Portion of four corallites of Fai-osites Gothlandica, Lamarck, enlarged, show ing the tabulae and the mural pores. The affinities of the great and important reef-building genus, Millepora, are still not absolutely settled. By Professor Louis Agassiz it was taken out of the true corals and placed amongst the Hydrozoa, and the most recent researches of Mr Mosely upon the living animal appear to corroborate this view. According to this observer, the spongy corallum is composed of calcareous trabeculse dis posed in layers concentric with the surface of the mass, and there is the unique feature that these layers are penetrated by a series of ramifying and anastomosing canals, which communicate with the calicular cavities. There are two kinds of calices in the species examined, large and small, the former being surrounded each by a ring of the latter. The polypes, or zob ids, are of two kinds, the larger ones, occupying the large calices, having a mouth and from four to six knobbed tentacles. The smaller zob ids are more slender, have no mouth, and have from five to twenty tentacles. Mr Mosely appears to consider that the struc ture of Millepora, as examined by him, is Hydrozoan ; but a recent investigation carried out, on the other hand, by Major-General Nelson and Professor Martin Duncan leads these authors to the opinion that Millepora is really Alcyonarian, and therefore truly referable to the Actinozoa. The genus Heliopora has recently been examined by Mosely in its living condition, and it has been shown to ba