Larrie Stone

Larrie Stone

Nudibranchs are a group of bottom-dwelling, soft-bodied marine mollusks that are grouped with snails and slugs in the class Gastropoda. They differ from snails by not having a shell. They shed their shells after their larval stage and end up with naked or exposed gills from which they derive their name.

Usually nundibranchs are carnivorous feeding on other small marine animals. Adorned with frond-like appendages, they look like brightly colored tropical flowers. Many species display beautiful patterns in a diverse array of vivid colors, and they are special targets for marine photographers the world over. They are found from the poles to the Tropics in both shallow and deep water.

However, their soft bodies and vivid colors make them a predator's delight. They are in need of some form of protection in order for each species to survive. Some species use camouflage in order to blend in with their environment. Other species have utilized their bright coloration in order to signal potential predators that they can be dangerous to eat.

One such defense is a chemical one in which the nudibranch tissues of certain species can contain either distasteful or poisonous chemicals. Typically, nudibranchs do not produce their own chemical defenses, but rather obtain them from their food sources. For example, some sponges contain either distasteful or poisonous chemicals in their tissues. Some species of nudibranchs are immune to these chemicals. When they eat the sponge, these chemicals can be recycled and deposited in the nudibranch's tissues to make it less palatable or actually poisonous to a predator.

Other species that feed on jellyfish, corals, and sea anemones that have a special type of "sting cell" as part of their defense system provide another type of nudibranch defense. Normally, when anything touches the tissue where a sting cell is located it explodes and sends out a harpoon-like thread with a sharp barb on its end. These barbs can either capture or irritate the organism it strikes, inject a toxin, or release a sticky substance that can entangle the prey.

Some nudibranch's have the ability to avoid discharging these sting cells when eating the tissues that contain them. The sting cells are then deposited in selected tissues of the nudibranch where they can discharge when a predator attacks it.

Larrie Stone is a retired Dana College science professor.

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