I am at war. My foe is a formidable opponent, cunning, resourceful and extremely persistent. My foe is a mollusc, one of an ancient group of animals that has inhabited this planet for millions of years, and I know I am not alone in my battle. Under the cover of darkness, black slugs, riding on a track of thick slime, are on a rampage against my tomatoes and strawberries. Night after night they keep coming despite my best efforts to deter them. Thankfully, most of the world's molluscs inhabit the oceans and seem to have a purpose beyond the wanton destruction of my garden.

The oceans of the world are an arena for the bizarre and the beautiful, an endless parade of animals all seemingly trying to outdo each other with colour and form. If nothing else, they make us take notice and appreciate the diversity and beauty that surrounds us. Some of the most beautiful and fascinating of these are the nudibranchs, or sea slugs, one of the orders of ophistobranch gastropod molluscs.

Nudibranchs are a common sight, with over 3000 known species scattered throughout all oceans of the world. Like jewels sprinkled over the sea-bed, nudibranchs are a prize for the underwater photographer and naturalist. Their diversity of form is amazing. They range in size from a few millimetres to over 30 centimetres in length. Some are to the mollusc what the peacock is to birds, announcing their presence with a dazzling display of fleshy appendages or brilliant colours, while others may live most of their lives buried beneath the substrate. There are also those that hide in plain view by mimicking the colour and texture of their surroundings, and a few even choose a life adrift in the open ocean.

The order Nudibranchia is divided into four suborders, the Dorids, Aeolids, Dendronotids and Arminids, each with its particular identifying characteristics, some subtle, some obvious. Dorids are characterized by being round or oval and rather flat without any fleshy appendages except for a lacy circlet of gills on their back that can be retracted when the animal is disturbed. Aeolids, and their cousins, the Dendronotids, on the other hand, are show-offs. Their slender bodies are decorated with showy, finger-like projections along their back, called cerata, used mainly for respiration but they may also contain branches of the digestive gland and defence mechanisms. All nudibranchs possess two hornlike sensory organs on top of their head called rhinophores which come in a wide variety of sizes and shapes.

The nudibranch's body structure can give the observer an insight to the animal's life style, favoured surroundings and even diet. Their ventral surface is comprised of a muscular foot which is used for locomotion. The Dorids have a broad foot and stay attached to the bottom at all times whereas the aeolids have a narrow foot and are capable of climbing up small sponges or corals. Dendronotids also have a slim body and foot, and some are capable of swimming by using an undulating motion of their bodies.

The nudibranch's seeming fragility belies a voracious carnivore. Nudibranchs can be specific feeders, choosing a diet of only one thing, or omnivorous to the point of cannibalism. The mouth is located on the nudibranch's ventral surface and most feed by the use of the radula, a series of chitinous teeth used to grind away at their prey and slowly chip off little mouthfuls. Most of the dorids are grazers of stationary prey such as barnacles, anemones, sea pens, sponges and corals. They lack strong jaws and rely heavily on the radula for feeding. However the Aeolids and Dendronotids feed on more motile animals such as tube dwelling anemones or other nudibranchs. Their radulas are reduced and they possess strong jaws for holding their prey. The large Dendronotus, or swimming nudibranch, creeps up slowly to the base of a tube dwelling anemone and when in range rears up like a cobra. The folds of skin around the head pull back, exposing the powerful jaws as it thrusts its head into the centre of the anemone. The
anemone immediately pulls back into its leathery sheath often dragging the front portion of the nudibranch with it but, seconds later, the nudibranch emerges with a tasty mouthful of tentacles. Some Dendronotids use a pumping action of the buccal sac or mouth cavity to suck their prey in like a vacuum cleaner. One nudibranch has no radula at all and has developed another way of feeding. Every Spring and Fall, tens of thousands of hooded nudibranchs occupy kelp forests and eel grass beds along the (BC) coast. It is an amazing sight to see these small creatures with their large diaphanous hoods deployed in order to capture prey.

Nudibranchs are gelatinous, little creatures, seemingly helpless, but nothing could be further from the truth. They have devised some ingenious methods for defence. Some, because of tiny size, cryptic coloration or preference for a life buried in the sand, are overlooked. But others seem to go out of their way to be noticed with brilliant colours and long appendages. These bright colours may serve as a warning against a truly ingenious method of defence. Some of the nudibranchs' prey, such as anemones, sponges and hydroids contain very effective defences of their own, such as packets of harpoon-like stinging cells called nematocysts which are fired at an attacking predator. But the nudibranch has the ability to ingest many of these cells without triggering them. It is theorized that the effect of those that are fired during this procedure are buffered by the nudibranch's mucous. The ingested packets of nematocysts are then transferred to the cerata and stored for use in defence of the nudibranch. It is interesting to note that a prey item may contain several different kinds of nematocysts but the nudibranch is capable of selecting only the most lethal type for storage.

But not all nudibranchs rely on others to fight their battles. Some Atlantic species release a small amount of sulfuric acid as a defence.

Most nudibranchs are hermaphroditic. This makes a potential mate of every other animal of the same species and increases the chance of successful propagation. Mating may last anywhere from a few minutes to several hours and results in cross fertilization of both animals. Nudibranch egg masses are very characteristic and some can even be identified to species. Dorid egg masses are ribbon shaped and usually laid in neat spirals whereas the Aeolids and Dendronotids lay a tangled mass of egg string. The number of eggs, depending on the species, can range from a few to a few hundred thousand.

Within two to six weeks of being laid the eggs develop into either a fully developed juvenile or a free swimming larval stage that undergoes metamorphosis after finding a suitable location.

Nudibranchs are short lived with most living only a few months and most species die after spawning. But in their short lives they give us a glimpse into a small part of the beautiful and fascinating world we share. Now, if I can only find some redeeming quality in those slugs in my garden.