Nautilus

• Chambered Nautilus (Nautilus pompilus) - 20cm

The nautilus is the most primitive of all cephalopods and has been around for at least 400million years. It has 90 arms and has no suckers so it relies on its shell for protection and also for buoyancy control. Within the shell are chambers that help regulate their buoyancy. This is important for the nautilus because during the day, it stays down at 1,000 - 1,500m and at night, it floats up to shallower waters to feed where it may be easier to find its favourite food such as carrion and moults of crustaceans

Nudibranchs

Nudibranchs are commonly known as sea slugs. Unlike other gastropods they do not have protection of shells or hard casing. Like the garden slugs, they are soft-bodied creatures that use their appendages to crawl over corals and rock surfaces in search of their staple diet.

Some species are strictly vegetarian but most are carnivorous feeding on nematocysts of coral polyps, anemones, sponges, hydroids etc.

These small, seemingly defenceless creatures are found aplenty in tropical waters where coral life is teeming. Nudibranchs are extremely colourful. The mixtures of bright colours are used to blend into the equally colourful environment where they feed. Some species adopt brilliant coloration to ward off would-be predators. These creatures on the underside are not defenceless at all…. they

produce highly toxic substances to protect themselves and traffic light warning colours to warn predators. Nudibranchs consume nematocysts ( the stinging cells of coral polyps and their main defence mechanism) with glee and do not seem to have any side effects on these creatures at all. Nematocysts sets off tiny explosive

charges when provoked but somehow the Nudibranchs have an ability to avoid setting off these explosives. Instead, the creature stores the venom cells in little special sacs on their backs. Which means that the nematocyst's 'sting' has been transferred onto the Nudibranchs for its own protection. Some Nudibranchs produce their own toxins, which they secrete through their skin and others
produce foul tasting substances.

Photos courtesy of Mr. Motti Uttam - Sipadan 2003

Nudibranchs are all hermaphroditic producing both eggs and sperms in their reproductive organs. Like all hermaphrodites, they do copulate with others of the same species, cross-fertilising each others' eggs - to ensure genetic continuance. The Nudibranch lays eggs that are just as colourful…laying huge numbers of eggs that are arranged in gelatinous, spiral ribbons in long strings or frilled like a woman's garter.

The lovely Spanish Dancer's name describes best the manner in which it undulates its skirt-like fringe when it swims far above the bottom in shallow water. This Nudibranch is the largest of these specimens and can grow to a length of 60cm(24in). It feeds on a wide variety of sponges and sometimes is seen washed ashore on beaches. Although the Spanish Dancers are hermaphrodites, they never self-fertilise. Sperm sacs are exchanged during copulation and may take days or even weeks before fertilisation occurs.

This specie is common at Pulau Redang. A prime example of the Nudibranch which means 'naked gills', this creature is brightly painted mauve and contrasted with a white lining. The gills are visible at one end and the antenna at the other end.

Found amongst its favourite food, sponges of all variety in depth ranges of between 3 and 20m. It has bright orange gills and antenna with light and dark blue markings in its central body with are bright orange band lining its margin.

The Aeolid has lots of thin, finger-like projections lining its body used to store the venom from the nematocysts it ingests and recycle for its own protection from predators. The nematocysts venom is stored in special venom sacs at the tip of the projections.

Clams

• Giant Clams (Tridacna crocea) - 60cm

There are 7 known species of giant clams belonging to the tridacnidae family. The Tridacna gigas specie is known to grow a diameter of 1.5m (5ft) and is believed to live as long as 200years! Tridacna crocea is the smallest specie of the giant clams, living in cracks on shallow reef areas and at times completely surrounded by live corals. Sometimes, only the mantle is visible when the clam is open. This mantle is a soft, fleshy organ that lines the inner shell. The mantle tissue contains algal cells, zooxanthellae that produce food for the giant clam. The mantle also contains light and pressure sensitive cells that signal the clam to close up when it is disturbed.

Scallops

The coral scallop, like the giant clams lodge themselves in cracks among colonies of live corals and usually only the mantle and shell opening can be seen. The beautifully coloured blue mantle is dotted with bright red spots and these are the light and pressure sensitive cells that signal the animal to close when disturbed.

Bivalves are named as they have two equal sized shells, which are hinged at one end to allow them to shut them together when disturbed. They do not move much once they have lodged themselves in one place therefore they rely on their gills to filter out plant and animal material. Water is pumped into an in-current siphon, pulled through the animal and finally expelled via an excurrent siphon.

Illustrations provided by Dennis Ho: Underwater photography by Moti Uttam

| Corals - Hard & Soft Corals | Eels | Sharks | Rays | Octopus | Squids and Cuttlefish | Nautilus | Nudibranchs | Clams | Starfish | Brittlestars | Featherstars | Sea Urchins | Sea Cucumbers | Worms | Sponges | Jellyfish | Damselfish | Butterflyfish | Angelfish | Surgeonfish | Parrotfish | Wrasse | Triggerfish | Batfish | Trumpetfish | Squirrelfish | Catfish | Grouper | Athias | Sweetlips | Fusiliers | Puffers | Filefish | Trevally | Snappers | Scorpionfish | Cardinalfish | Goby | Barracuda | Rainbow Runner | Pompano | Bream | Goatfish |