parapodium

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One of the fleshy paired appendages of polychaete annelids that function in locomotion and breathing.
• noun A winglike extension of the foot of certain gastropods, such as the sea butterflies, used for swimming.

from The Century Dictionary.

• noun One of the unjointed lateral locomotor processes or series of foot-stumps, foot-tubercles, or rudimentary limbs of many worms, as annelids.
• noun [capitalized] In entomology, a genus of hymenopterous insects of the family Crabronidæ, erected by Taschenberg in 1869 for a single species from Venezuela.
• noun In gastropods, a fin-like expansion of the foot; an epipodium.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) One of the lateral appendages of an annelid; -- called also foot tubercle.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun zoology Paired unjointed lateral outgrowths used for locomotion by worms such as annelids.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun one of a pair of fleshy appendages of a polychete annelid that functions in locomotion and breathing