A acanthurid Member of the family Acanthuridae. aerobic The presence of, or requiring oxygen. See Also: anaerobic ahermatypic Corals that do not have zooxanthellae. See Also: hermatypic algae Any of the various, mostly aquatic, photosynthetic organisms in the kingdom Protoctista. anaerobic Containing little or no oxygen. See Also: aerobic anal See anal fin. anal fin Single fin located on the ventral side of a fish, posterior of the anus. animal Member of the taxonomic kingdom Animalia. Animalia Taxonomic kingdom consisting of all animals (living or extinct). annelids Members of the taxonomic phylum Annelida consisting of segmented worms. This includes earthworms, leeches, and a large number of mostly marine worms known as polychaetes. annular Shaped like or forming a ring. anterior Located near or towards the head. See Also: posterior appendage A major projection from the body of an animal. aquatic Relating to, or living in water. arthropods Members of the taxonomic phylum Arthropoda consisting of insects, spiders and crabs. atoll A ring-shaped reef surrounding a lagoon.