They contain corals, but are not coral reefs.
C. corals, from the S.
Nemertines live in the sea, some being common amongst the corals and algae, others hiding in the muddy or sandy bottom, and secreting gelatinous tubes which ensheath the body along its whole length.
They are ridges of aeolian limestone plastered over by a thin layer of corals and other calcareous organisms. The very remarkable "serpuline atolls" are covered by a solid crust made of the convoluted tubes of serpulae and Vermetus, together with barnacles, mussels, nullipores, corallines and some true incrusting corals.
Corals, both reef-builders and others, flourished in the clearer waters; rugose forms are represented by Amplexoid, Zaphrentid and Cyathophyllid types, and by Lithostrotion and Phillipsastraea; common tabulate forms are Chaetetes, Chladochonus, Michelinia, &c. Amongst the echinoderms crinoids were the most numerous individually, dense submarine thickets of the long-stemmed kinds appear to have flourished in many places where their remains consolidated into thick beds of rock; prominent genera are Cyathocrinus, Woodocrinus, Actinocrinus; sea-urchins, Archaeocidaris, Palaeechinus, &c., were present; while the curious extinct Blastoids, which included the groups of Pentremitidae and Codasteridae, attained their maximum development.
A, without, and Rropos, passage), a biological term meaning imperforate, or not porous: there is a group of corals called Aporosa.
Corals and other quick-growing cal- careous marine organisms are the most powerful in this respect by creating new land in the ocean.
The later beds of the island belong to the Jurassic, Cretaceous and Tertiary systems. At the western foot of the Ida massif calcareous beds with corals, brachiopods (Rhvnchonella inconstans, &c.) have been found, the fossils indicating the horizon of the Kimmeridge clay.
The corals are few in number, but the Molluscoida (Polyzoa) are more numerous in species and individuals.
Corals would now grow luxuriantly in these shallow coastal waters of increasing temperature, forming reefs and extensive coral flats.
Japan is not rich in corals and sponges.
Her most interesting contributions are crust-corals (Gorgonidae, Corallium, Isis, &c.), and especially flint-sponges, called by the Japanese hoshi-gai and known as glass-coral (Hyalonema sieboldi).
Waves and tidal currents produce their full effects in that region, and in high latitudes the effect of transport of materials by ice is very important; while in the warm water of the tropics the reefbuilding animals and plants (corals and calcareous algae) carry on their work most effectively there.
When the proportion of calcium carbonate in the blue mud is considerable there results a calcareous ooze, which when found on the continental slope and in enclosed seas is largely composed of remains of deep-sea corals and bottom-living foraminif era, pelagic organisms including pteropods being less frequently represented.
De Pourtales pointed out in 1870; they consist of remains of deep-sea corals, serpulae, echinoderms and mollusca united Sands, gravels, muds, &c.
North America is bathed in frigid waters around its broad northern shores; its mountains bear huge glaciers in the north-west; the outlying area of Greenland in the north-east is shrouded with ice; and in geologically recent times a vast ice-sheet has spread over its north-eastern third; while warm waters bring corals to its southern shores.
South America has warm waters and corals on the north-east, and cold waters and glaciers only on its narrowing southern end.
The Hydrozoa are thus shown to belong to the group of Coelenterata Cnidaria, and it remains to consider more fully their distinctive features, and in particular those which mark them off from the other main division of the Cnidaria, the Anthozoa, comprising the corals and sea-anemones.
In the central and western Pacific the northern and southern limits of the occurrence of reef-forming corals are approximately 30 N.
Here the broad distinction has been drawn between volcanic and coral islands; but this requires amplification, both because the coral islands follow more than one type, and because the work of corals is in many cases associated with the volcanic islands in the form of fringing or barrier reefs.
At the southern end of the peninsula is a series of coral islands, known as keys; they appear to be due to the forward growth of corals and other lime-secreting organisms towards the strong current of the Gulf Stream, by which their food is supplied:
The departure of the Ordovician life from that of the Cambrian was perhaps most pronounced in the great development of the molluscs and crinoids (including cystoids), but corals were also abundant for the first time, and graptolites came into prominence.
Corals, echinoderms, brachiopods and all groups of molluscs abounded.
Among the more important features of the marine life of the period were (1) the great development of the molluscs, especially of cephalopods; (2) theabundanceoflargebrachiopods; (3) theaberrant tendencies of the trilobites; (4) the profusion of corals; and (5) the abundance, size and peculiar forms of the fishes.
CORALS (KoRAIS), ADAMANTIOS [in French, DIAMANT
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.
Fossil corals fix the geological age of the rock.
The groups of organisms utilized for zoning and correlation by different workers include brachiopods, pelecypods, cephalopods, corals, fishes and plants; and the results of the comparison of the faunas and floras of different areas where Carboniferous rocks occur are generalized in the table below.
- Numerically, the most important inhabitants of the clear Carboniferous seas were the crinoids, corals, Foraminifera and brachiopods.
The old land area still existed to the north, but doubtless much reduced in height; against this land, detrital deposits still continued to be formed, as in Scotland; while over central Ireland and central and northern England the clearer waters of the sea furnished a suitable home for countless corals, brachiopods and foraminifera and great beds of sea lilies; sponges flourished in many parts of the sea, and their remains contributed largely to the formation of the beds of chert.
The abundance of corals in some of the Carboniferous seas and possibly also the large size of some of the Productids and foraminifera may be taken as evidence of warm or temperate waters.
Balmae, on the southern shore of Kirkcudbrightshire, the coast south of Girvan and the limestone quarries of the Stinchar and Girvan valleys, in Ayrshire, for shells, trilobites, corals, &c.
Corals, Archaeocyathus, Spirocyathus, &c., lived in the Cambrian seas along with starfishes (Palaeasterina), Cystideans, Protocystiles, Trochocystites and possibly Crinoids, Dendrocrinus.
In the subdivision Anthozoa, comprising the sea-anemones and corals, the individual is always a polyp; in the Hydrozoa, however, the individual may be either a polyp or a medusa.
The reef-building corals are polyp-colonies, strengthened by the formation of a firm skeleton.
For figures of polyps see P. Gosse, A History of the British SeaAnemones and Corals (London, 1860); A.
Although corals have been familiar objects since the days of antiquity, and the variety known as the precious red coral has been for a long time an article of commerce in the Mediterranean, it was only in the 18th century that their true nature and structure came to be understood.
The structure and classification of polyps, however, were at that time very imperfectly understood, and it was fully a century before the true anatomical characters and systematic position of corals were placed on a secure basis.
This gives off new outgrowths, and these, branching and anastomosing with one another, may form a network, adhering to stones, corals, or other objects, from which FIG.
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.
As far as the anatomy of the zooid is concerned, the majority of the stony or madreporarian corals agree exactly with the soft-bodied Actinians, such as Actinia equina, both in the number and arrange 4 4 ¢ 2 4 FIG.
All recent corals, as has already been said, conform so closely to the anatomy of normal Actinians that they cannot be classified apart from them, except that they are distinguished by the possession of a calcareous skeleton.
The septa in recent corals always bear a definite relation to the mesenteries, being found either in every entocoele or in every entocoele and exocoele.
The larvae of corals are free swimming ciliated forms known as planulae, and they do not acquire a corallum until they fix themselves.
In others the peripheral ends of the septa are united only by bars or trabeculae, so that the theca is perforate, and in many such perforate corals the septa themselves are pierced by numerous perforations.
(C original; the rest after von Koch.) aporose corals, the only communication between the cavity of the edge-zone and the general cavity of the zooid is by way of the lip of the calicle; in the latter, or perforate corals, the theca is permeated by numerous branching and anastomosing canals lined by endoderm, which place the cavity of the edge-zone in communication with the general cavity of the zooid.
A large number of corals, both aporose and perforate, are colonial.
In division a vertical constriction divides a zooid into two equal or unequal parts, and the several parts of the two corals thus produced are severally derived from the corresponding parts of the dividing corallum.
In colonial corals a bud is always formed from the edge-zone, and this bud develops into a new zooid with its corallum.
Corals have been divided into A porosa and Perforata, according as the theca and septa are compact and solid, or are perforated by pores containing canals lined by endoderm.
Various attempts have been made to classify corals according to the arrangement of the septa, the characters of the theca, the microscopic structure of the corallurn, and the anatomy of the soft parts.
The lastnamed method has proved little more than that there is a remarkable similarity between the zooids of all recent corals, the differences which have been brought to light being for the most part secondary and valueless for classificatory purposes.
On the other hand, the study of the anatomy and development of the zooids has thrown much light upon the manner in which the corallum is formed, and it is now possible to infer the structure of the soft parts from a microscopical examination of the septa, theca, &c., with the result that unexpected relationships have been shown to exist between corals previously supposed to stand far apart.
This has been particularly the case with the group of Palaeozoic corals formerly classed together as Rugosa.
The Hydrozoa comprise the hydroids, so abundant on all shores, most of which resemble vegetable organisms to the unassisted eye; the hydrocorallines, which, as their name implies, have a massive stony skeleton and resemble corals; the jelly-fishes so called; and the Siphonophora, of which the species best known by repute is the so-called "Portuguese man-of-war" (Physalia), dreaded by sailors on account of its terrible stinging powers.
Neomenia and its allies are marine animals living at depths of 15 to Boo fathoms on soft muddy ground; they are found crawling on corals and hydrozoa, on which they feed.
The cavities both of the calices and coenenchymal tubes of Heliopora are closed below by horizontal partitions or tabulae, hence the genus was formerly included in the group Tabulata, and was supposed to belong to the madreporarian corals, both because of its lamellar skeleton, which resembles that of a Ma.drepore, and because each calicle has from twelve to fifteen radial partitions or septa projecting into its cavity.
(3) The theca or wall, which in many corals is not an independent structure, but is formed by the conjoined thickened peripheral ends of the septa.
(6) Epitheca, an offset of the basal plate which surrounds the base of the theca in a ring-like manner, and in some corals may take the place of a true theca.
In addition to these parts the following structures may exist in corals:- Dissepiments are oblique calcareous partitions, stretching from septum to septum, and closing the interseptal chambers below.
Hence in corals in which there is only a single cycle of mesenteries the septa are correspondingly few in number; where several cycles of mesenteries are present the septa are correspondingly numerous.
In some corals, in which all the septa are entocoelic, each new system is embraced by a mesenteric couple; in others,in which the septa are both entocoelic and exocoelic, three septa are formed in Il FIG.
In some corals the septa are solid imperforate plates of calcite, and their peripheral ends are either firmly welded together, or are united by interstitial pieces so as to form imperforate theca.