A CLUMP OF STAG'S-HORN CORAL.
The life-colours of this coral are a delicate cream with brilliant magenta tips.
Photo by W. Saville-Kent, F.Z.S.] [Milford-on-Sea.
BLEACHED CORALS FROM THE GREAT BARRIER REEF.
Branching stag's horn corals are chiefly represented in this group. Several of the large solitary mushroom-corals may, however, be observed in the foreground.
An ordinary coral-animal or polyp, as previously stated, differs in no respect from a sea-anemone, excepting for the possession of a calcareous skeleton secreted within its basal tissues, including portions of the membranous radiating partitions. Some coral-animals, like the majority of the Anemones, are solitary, and form single attached or loosely lying corals. The well-known Mushroom-coral is one of the latter. One species observed, which was photographed through the water by the writer as it lay expanded in a tide-pool on the Australian Great Barrier Reef, might easily be mistaken for a big sea-anemone allied to the dahlia-anemone. On being disturbed, however, it immediately shrinks back upon its base, ejecting all the water with which its expanded tissues were filled, and revealing the presence of the hard radiating coral beneath. Each of the calcareous radii, which are now clearly defined through the thin semi-transparent skin, corresponds in position with one of the internal membranous partitions, and also with the origin of one of the tentacles. New mushroom-corals are produced as buds thrown off from the parent, which attach themselves and secrete a foot-stalk, to which they remain affixed, like the young of the feather star-fish, for the earlier epoch of their existence. Ultimately, however, they become detached, and, falling from their stalks, lie loosely on the sea-bottom, after the manner of their parents. The huge coral-masses commonly known as Madrepores, out of which coral-islands and reefs are constructed, all commence as a single coral-animal, with its contained skeleton analogous to the mushroom-coral, though in all instances much smaller. The buds developed by the coral-polyp in these instances remain attached to the parent. If they spread out laterally, they build up by accumulation the large flattened or sub-spherical masses known as Brain-corals and Star-corals, which are most abundant on coast-line reefs, or form the bases of the outer barrier-reefs. Where, on the other hand, the budding is terminal or oblique, branching tree-like growths such as the Stag's-horn Corals, with their innumerable allies and variations, are produced. The colours of the coral-polyps are as brilliant and diverse as those of ordinary sea-anemones, living reefs, whereon a number of different species are in a condition of healthy growth, yielding a spectacular effect that vies with that of any floral parterre. Sometimes large areas, acres upon acres in extent, may be covered with one almost uniform purple, green, brown, or other coloured growth of the branching stag's-horn species. The aspect presented is not unlike that of a heath-covered common.
In addition to the solid, calcareous-skeletoned Madrepores, or "Stony Corals," as they are often termed, there are a number of species in which a skeleton composed only of loosely aggregated calcareous spicules is produced. The so-called Flexible Corals, or Sea-fans, belong to this category, as also the precious Coral of Commerce. In the last-named species the solid, brilliantly coloured skeleton so much prized as an article of jewellery is deposited as a supplementary basis outside the tissues by which the star-patterned skeletons of the stony corals are secreted.
Photo by W. Saville-Kent, F.Z.S.] [Milford-on-Sea.