or mouthpart, and then pokes its proboscis into this opening to feed on the fleshy tissues within. Another species, with similar tastes in prey, is the drill (Thais). This small gastropod literally drills a hole through the oyster's shell. The large number of bivalve shells with neat holes drilled in them that are washed up on Indonesian beaches testifies to the efficiency of this feeding method.
Tritons. The triton shell (Charonia tritonis) is famous as a predator of the troublesome crown-of-thorns starfish, which has devastated Australian reefs. This large shell (to more than 30 cm.) is a popular souvenir, and over-harvesting has been blamed for population explosions of the crown-of-thorns. The helmet conch (Casis cornuta) is another large, predatory gastropod found in Indonesia. Because of collectors, both the triton and helmet conch are endangered in parts of Indonesia.
Cone shells. Cone shells (Conus spp.) are even more rapacious predators. Their radulas are modified as barbs, with which they stab their victims. They then immobilize their prey by injecting a neurotoxic poison. Most cone shells eat worms, although a few are piscivorous. The poison of some of the fish-eating Conus species is powerful enough to kill a human, so treat them with respect.
A predatory gastropod prying open a bivalve.
Cowries. Cowries (Cypraea spp.) are common, small (most just a few cm.) gastropods with a smooth shell that is completely covered by the animal's fleshy mantle. Both the shells and mantles can be beautifully marked, often with very different patterns. The cowries are omnivorous, feeding on algae as well as a variety of sedentary animals such as soft corals.
Clownfish and their Sea Anemone Hosts
There is perhaps no sight more charming than a pair of bright clownfishes nestled in one of the colorful giant reef anemones. Although known to possess powerful stinging cells, the anemones clearly don't harm the clownfishes, which look downright snug tucked into the soft tentacles of their host.
The colorful magnificent anemone, one of the largest clown-fish anemones.
The relationship between the fish and the actinian is commensal; the anemonefishes clearly benefit, receiving protection for themselves and their offspring. They even pluck at the tentacles and oral disk of the anemone, eating the organic material that has collected there.
The benefit to the anemone is less clear. The constant prodding, cleaning and stimulation provided by the fishes certainly seems enjoyable, but this maybe just to us. Anemonefishes are never found without anemones; anemones, however, are sometimes found without the fish.
A Delicate Operation
It had been thought that clown-fishes were somehow immune to the anemone's stinging nematocysts. Close observations, however, have shown this not to be the case. The fish, through a series of brief—and careful— encounters with the actinian, picks up a substance in its mucous that the anemone recognizes as its own. The nematocysts don't fire when touched by the fish for the same reason one tentacle doesn't sting another.
Some cold-hearted experimenters tested this theory by scraping the mucous off a clown-fish and placing it back with its anemone. The hapless fish was immediately and unceremoniously stung.
Juvenile Clark's anemone-fish, in the distinctive bulb-tentacled anemone. 15 meters, Bunaken Island, Sulawesi.
Clownfishes are protandrous hermaphrodites; that is, all mature as males, and then a few sex-reverse to females. A typical anemone will contain a pair of clownfish, and perhaps a few young ones.
The largest fish in the group is the female. If she should die, the reigning male sex-reverses, and the dominant juvenile becomes the functional male. Juveniles sharing an anemone with an adult pair are hormonally stunted, and remain small.
Although clownfish are the only fishes to require an anemone host, other small damsels will opportunistically occupy anemones as juveniles, especially various species of Dascyllus.
Young Clark's anemonefish, Amphiprion clarkii, in the distinctive sand anemone, Heteractis aurora.
The spine-cheek anemone-fish, in the bulb-tentacled anemone. The spine-cheeked anemonefish varies from red to almost black.
A pair of Amphiprion ocellaris, in Haddon's anemone. This is not a known association in the wild.
Sea Anemones
Some of the giant reef anemones can reach a meter in diameter. All have zooxanthellae, and are thus found in relatively shallow water. They derive most of their nutrition from the algae, but also consume plankton and any other small animal unlucky enough to blunder into their tentacles.
Anemones can live to a ripe old age. In the 19th century, British naturalist John Dalyell kept a coldwater Actinia sp. anemone for 66 years. Over this period, it produced 750 young (by budding), 150 of these after the age of 50. The anemone eventually outlived the scientist.
Some 10 species of Indonesian anemones, in three families, host clownfish. The systematics of this group was in some confusion until Dr. Daphne Fautin reorganized it in 1981.
Cryptodendrum adhaesivum. Lies flat; very short tentacles. Hosts only Clark's anemonefish.
Entacmaea quadricolor. The bubble anemone. (See photo at left.) Hosts 11 species.
Macrodactyla doreensis. Very long, widely spaced tentacles. Usually dull color, buries column in sand. Hosts 2 species.
Heteractis aurora. Dull color, buries column in sand. Distinctive tentacle shape (see top photo above.) Hosts 7 species.
H. crispa. Long, thin, almost pointed tentacles that often seem tangled. Hosts 11 species.
H. magnifica. Brightly colored column, blunt tentacles. Often photographed. (See small photo opposite.) Hosts 10 species.
H. malu. Buries column in sand, fairly short tentacles, limited range. Hosts only Clark's.
Stichodactyla haddoni. Haddon's carpet anemone. Short-tentacles. Grey, with white radial stripes. Hosts 6 species.
S. gigantea. Bludru anemone. Longer tentacles, larger than Haddon's. Hosts 6 species.
S. mertensii. Merten's anemone. Colorful; largest carpet anemone, to lm across. (See bottom photo above.) Hosts 10 species.
— David Pickell
One of the piscivorous cone shells (Conus sp.) devouring a small goby. Most cone shells eat worms, but the relatively few fish-eating species are very dangerous.
