What is a Soft Coral?
We must begin with a good definition of "soft coral" because the popular concept and literal meaning of the name are quite different from the actual definition. Taie soft corals all belong to the subclass Octocorallia. Like stony corals and anemones, the soft corals belong to the phylum Cnidaria and the class anthozoa. What distinguishes them is the number of tentacles on the polyps. All soft corals have eight tentacles on each polyp, hence the name Octocorallia. Exceptions to this rule only occur accidentally as deformities on a few polyps, individual anomalies, while the rest of the colony has normal, eight-tenta-cled polyps. Another distinguishing characteristic of these polyps is the presence of side branchlets called "pinnules'1 on each tentacle. The pinnules make the tentacles look like feathers, and they are thus called pinnate. Some soft corals have reduced pinnules or none at all, however. The construction of the polyp with eight unpaired mesenteries is also a characteristic of octocorallia.
The name "soft" coral is misleading since not all Octocorallia are soft. The "blue coral'1 Heliopora coerulea forms thick hard crusts, plates and heads of calcium carbonate with a high concentration of iron salts that stain the skeleton blue. The living animal is brown since it contains zooxanthellae. Without the polyps expanded it could easily be mistaken for fire coral, Millepora spp. which form similar mustard-coloured fronds and crusts. Another soft coral that forms a hard skeleton is Tubipora, "Pipe organ" coral. "Pipe organ" coral is a popular curio item because of its rich, deep red colour and odd structure composed of upright tubes and flat floor-like layers. The living coral is quite variable in appearance and although one species only, Tubipora musica, has been recognized for many years, at least four distinct species exist. In this book we show all of them. Octocorals
A rare and stunning soft coral, also form a variety of skeletal elements from tiny sclerites to axial
Siphonogorgiasp., photographed structures made of an organic material similar to horn, and from on a reef wall in the Solomon . , . r , , . . r
Islands J Sprung calcium carbonate. The sort coral genus .Smiliaria has a rew species
(including the common S. polydactyla) that can actually build a solid reef from fused sclerites called spiculite produced around their base. Columns of spiculite several meters high have been found on the Great Barrier Reef after storm sand movement, with live Sinularia colonies still growing on top (P. Alderslade, pers. comm.)! A proteina-ceous axial skeleton (gorgonin) is found in all Holaxonia gorgonians and in most sea pens (Bayer, 1973).
True soft corals have eight tentacles on each polyp, and the tentacles often look like feathers because of the fine side branches called pinnules. The polyps of Clavularia spp. are classic examples of these features that define soft corals (octocorallia). J. Sprung
Sometimes octocoral polyps develop "Siamese twin" heads with two mouths and more than eight tentacles. On occasion there are also deformities with only one mouth but more than eight tentacles. Note the polyp in the center with at least twelve tentacles. A. J. Nilsen
"Spiculite" rock made of fused scle-rites by Sinularia spp. This photo shows the inside composition. J. Sprung
The outer surface of the same piece of spiculite is smooth and hard. J. Sprung
A finely branched Sinularia sp. that produces spiculite at its base, forming hardened twigs. T. Siegel
It is common to see colonial zoan-thid anemones of the genera Zoan-thus, Palythoa and Protopalythoa referred to as "soft corals" because of their soft tissue and resemblance to true stony corals. However, they are neither soft corals nor stony corals. J. C. Delbeek
When scientists discuss soft corals, they usually refer to them as octocorals, and further subdivide these into other groups such as gorgonians and alcyonaceans. When they are thus subdivided, the term "soft coral" really only refers to the alcyonaceans such as Dendronephthya, Sarcophyton, Sinularia, Alcyonium, etc.
Fleshy stony corals such as Helio-fungia, Catalaphyllia and Euphyllia are sometimes called "soft" corals because of their soft fleshy tissues, but they are true stony corals, scle-ractinia. Heliofungia actiniformis is shown here. S. W. Michael
Corallimorpharians are often called "false corals" and sometimes "soft corals" because they look like corals, are soft and fleshy, and lack a skeleton. They are closely related to true stony corals and belong to the suborder Corallimorpharia. Ricordea florida is shown here. J. Sprung
These colonial zoanthids, Para-zoanthus spp., live in association with other invertebrates such as hydroids and sponges. They are often confused with soft corals or with black coral (antipatharians). J. Sprung
The Fire Anemone, Adinodendron has tentacles which look like soft coral branches, most similar to Nephthea spp. J. Sprung
The organ-pipe coral, Tubipora, is an octocoral that has a hard skeleton made of calcium carbonate and coloured red by mineral salts deposited with the calcium. Although it is considered closest to Pachyclavularia, it probably is most closely related to Clavularia spp. J. Sprung
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