Diving Indonesia Periplus Adventure Guid. David Pickell
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they are easy to identify as soft corals, but when their polyps are retracted they could be mistaken for sponges. The leather corals, however, have a much smoother surface than sponges.
Perhaps the most beautiful of the soft corals is Dendronephthya, a soft coral with fuzzy branches of vivid pink, white, orange, red, red-and-white, and a variety of other colors. The main "stem" is normally translucent and contains numerous white spicules, which offer some structural support. Most of the color comes from the polyps, which also contain sharp spicules to deter browsing by fishes. Dendronephthya grows deeper on the reef and in areas of low light, and always where currents can provide it with abundant plankton.
Xenia, particularly common in Indonesia, has perhaps the largest individual polyps of any soft coral, each 6-8 centimeters long. The white (also tan, or light blue) polyps grow in clusters, and the tentacles at the end of each are feathery. These continually open and close, like numerous grasping hands. In Xenia one can easily count eight tentacles, which is one feature that distinguishes soft corals (Octocorallia) from hard corals and anemones (Zoantharia) which have six, or multiples of six, tentacles.
Gorgonians. Gorgonians (order Gorgonaceae) have a strong, horny skeleton, which gives strength and support without sacrificing flexibility. They tend to grow on the deeper parts of the reef, away from strong wave action. They live by filter feeding, and to maximize the water flow across their surfaces always grow at right angles to the prevailing current. Where the tidal current flows along the reef, gorgonians grow with their long axis vertical. Sometimes, however, particularly on some of the big walls in Indonesia, large sea fans can be seen growing horizontally out from the reef wall, to take advantage of the current upwelling.
There" are many species of these animals. Some have a twig-like structure, like a branch from a delicate tree. Many are brightly colored. The sea fans (Melithaeidae and Plexauridae) are flat nets, growing in some cases to three meters across. The skeleton of a sea fan is coated with a kind of "rind," which is sometimes a delicate shade. When you see a big gorgonian it is worth spending a few moments looking closely at its surface because they often host an assortment of small symbiotic animals.
Sea pens. These animals (order Pennatulacea) are filter-feeders related to the gorgonians. Their common name comes from their resemblance to the old-fashioned quill pen. Although common in Indonesia, they are not really reef dwellers, and will usually only be seen by night divers who venture out over mud or sand bottoms. Sea pens, sometimes growing in large fields, rotate gently back and forth with the current, their "feathers" sifting plankton from the current.
Closeup of the lovely soft coral Dendronephthya. In this photograph the strengthening spicules are clearly visible in the animals ' transparent tissue.
The poisonous sea wasp, Chironex. This animal has been responsible for human fatalities in Australian waters.
Black corals. Black coral (subclass Ceriantipatharia, order Antipatharia) looks to the diver like a gorgonian, although it is more closely related to the stony corals and anemones. On deeper dives in Indonesia, one can see wire corals (Cirrhipathes) and black coral bushes (Antipathes).
The polished skeleton of the latter, particularly the thicker branches, is the precious black coral. Black coral is scarce, and its export from Indonesia and import into many other countries is prohibited by laws.
Cerianthids. In some areas, particularly with sandy bottoms, one can find cerianthids (subclass Ceriantipatharia, order Ceriantharia) or tube anemones. These are quite different from true anemones. Cerianthids have fine tentacles arranged in two concentric bands, and a tube— made of fibers created by special nematocysts—into which they can retract if disturbed.
A pair of Chromodoris willani, perhaps mating. All nudibranchs are hermaphrodites, although they require a partner to produce viable off-spring. Bunaken group, Sulawesi.
Fire coral and hydroids
All cnidarians have stinging cells on their tentacles with which they can defend themselves and immobilize their prey. In most cases, however, these are rather weak and are usually not capable of penetrating human skin. One group, class Hydrozoa, which includes the fire corals and their relatives, has members capable of inflicting very painful stings. The notorious Portuguese-man of-war (Physalia physalis) is a hydrozoan, and not, despite its appearance, a jellyfish. Fortunately for divers this animal is more of an open ocean dweller.
Stinging hydroids. A far greater nuisance to divers in Indonesia are the hydroids Aglaophenia and Lytocarpus. Despite their delicate, fern-like appearance, these colonial animals can deliver a burning sting that raises a welt on bare skin. They are fairly common on many Indonesian reefs, and their presence prompts divers to wear Lycra or thin neoprene suits even in the warmest of conditions. The stinging hydroids are sometimes called sea ferns, or sea nettles.
Fire corals. Somewhat less virulent are the fire corals of the genus Millepora, but as their name suggests they too should be treated with respect. These hydrozoans are members of a group called hydrocorals for their superficial resemblance to the true corals. Hydrocorals secrete a limestone skeleton, and form colonies that are usually a dull-yellow brown in color (Millepora) although some species (Distichopora, Stylaster) can be brightly colored.
The unusual blue coral (Heliopora coerulea), is a fire coral which has a skeleton that when dried displays a light blue tint. It is taxonomically distinct, however and has been placed in class Anthozoa with the octocorals.
Some hydrocorals are important reef-builders, particularly M. platyphylla, which can be found growing with massive scleractinian corals at the pounding edge of the reef.
Jellyfish
These familiar animals (class Scyphozoa) are characterized by a dominant medusa stage. Like all cnidarians they form a polyp for part of their lives, but for the jellyfish, this is just temporary. Occasionally, large jellyfish can be seen while diving in Indonesia, particularly in areas of rich plankton. These can be quite beautiful to observe. More bothersome are the cubomedusae, or sea-wasps, tiny jellyfish that can have an irritating sting. Members of the genus Chironex have even been responsible for human fatalities in Australia. Because they tend to inhabit the surface layer during the day, they are more of a bother for snorkelers. The lights of night divers, however, can often attract an unwelcome swarm of these creatures.
Worms
Although the word conjures up a dull, and faintly repulsive animal to many people, the worms found on the reefs of Indonesia show a diversity of form and color that often astounds the observer.
There are many different sorts of worms, but most likely to be seen by divers on Indonesian reefs are those in the following phyla: the flatworms (phylum Platyhelminthes); the ribbon-worms (phylum Nemertina); the tongueworms (phylum Echiura); and the segmented worms (phylum Annelida).
Flatworms. Flatworms often have the strikingly beautiful colors divers associate with nudibranchs (which are molluscs). The species seen on Indonesian reefs rarely grow longer than 10 centimeters, and feed on sessile animals such as tunicates and sponges. Flatworms move by gliding over the bottom, or by muscular undulations. This latter waving action is characteristic, and mimicked by the juveniles of several species of fish. This mimicry and the bright colors suggest the presence of a noxious chemical to deter predators.
Ribbonworms. These animals are longer than flatworms, and not as showy. Many are white, with dark stripes or bands. They tend to live under rocks and corals or in the sand, and are most likely to be seen by divers at night. Some can grow to astonishing sizes, as much as several meters. They feed on molluscs and other worms.
Tongueworms. The tongue-worm Bonellia can be seen on reef slopes. However, it hides its sac-like body in a crevice, with only a forked proboscis protruding, is easily overlooked. These animals have an unusual sex life. All the fully formed