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Although an order of Opisthobranchia (class Gastropada, Phylum Molusca) for organizational sake and the familiarity of non-marine biologists, I have classified the 8 orders of Opisthobranchs under the heading Nudibranchs.
These animals differ from marine snails in their evolution towards reduction, loss of shell and internalization. Some may be colorfully dramatic or invisible due to camouflage. Found in tropics and cold-water, these creatures total more than 3,000 species worldwide. While mostly shell-less some do have reduced or internal shells. All are found in salt water. When present, bright colors serve as a warning. Some secrete acids, giving off a foul taste. Others have nematocysts (stinging-cells) of anemones in their cerata, the finger-like projections found on the backs of certain species. The California Sea Hare can even squirt ink like squids. Opisthobranchs are both herbivores and carnivores - many adapted to eating only one certain species of plant or animal. They have rows of teeth, radula, which are shaped differently depending on the species' food source. Nudibranch means "naked gill" since the lungs of this order are found on the outside of the animal.
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marine mammals - molluscs - nudibranchs - seastars - sponges - homepage
