Definition from Wiktionary, the free dictionary
Jump to: navigation, search

The only sense given is not quite right[edit]

The only sense given in the definition today, 2010-04-08, is "An intracellular projection of a eukaryotic cell containing a microtubule array, used for locomotion." I don't believe that is quite right.

I believe that the biological community is using the term undulipodium to describe the set (of two) cellular organelles that are structurally identical but have historically been known by two different names: cilia and flagella.

The definition as given today would include all flagella, but only motile cilia -- it would exclude primary cilia (sometimes referred to as immotile cilia). But I don't have a good reference to prove this. Wikipedia has articles however on all three organelles.

More specifically, since cilia and flagella are structurally identical, and their two distinct names hearken back to when their microstructure and function were unknown—and the motile cilia and flagella were the only ones thought to be bilogically interesting because for many decades, primary cilia were (incorrectly, per research since the early 1990s) thought to be vestigial—the biology community seems to have now given the common name Undulipodium to the set of two structurally identical organelles.

I've extended the definition slightly, but I'm not a Biologist, and I don't think that I've addressed your concerns. Can you point us to a reference that uses your definition? Dbfirs 20:33, 8 April 2010 (UTC)
Note that only eukaryotic flagella are structurally identical to cilia. Bacterial flagella are not included in the definition of undulipodium. --EncycloPetey 20:55, 8 April 2010 (UTC)
Some documents seem to claim that cilia previously thought to be vestigial have a number of other functions, but I'm out of my depth here. Dbfirs 21:04, 8 April 2010 (UTC)
There's a great deal of argument, confusion, and puzzlement over the functions of many eukaryotic organelles. But fortunately, they all have names! --EncycloPetey 21:08, 8 April 2010 (UTC)
... so should we add "and possibly other functions" to our definition? Dbfirs 21:15, 8 April 2010 (UTC)
We could, but that's more speculative than informative. That qualifier would apply to a great many organelles. I don't think it benefits the entry. Carbonated water can be used to remove stains from cloth, but that doesn't help define what it is. Similarly, an undulipodium is defined by having a particular physical structure, not by its use. It would be better to list specific forms under a ====Hyponyms==== section and present functions on individual entries, as feasible. --EncycloPetey 21:17, 8 April 2010 (UTC)
So would our entry be better without any mention of use? We could leave it to Wikipedia to discuss the possible purposes/uses of the structures. Dbfirs 21:22, 8 April 2010 (UTC)
Since there is a key use commonly associated with them, yes, just as explaining that milk is a beverage is useful. Listing all the details and conjectures should be left to Wikipedia though. For example, there is an organelle called a haptonema in the Prymnesiophyta which, although similar to cilia / flagella, does not have exactly the same structure, and is not used for movement. It might fall within the definition of undulipodium or it might not. Either way, it's limited to one group that (for non-specialists) is obscure. We don't need to worry about that degree of coverage, but should present the key generalities. --EncycloPetey 21:29, 8 April 2010 (UTC)
How about inserting "typically" before our mention of uses, then we cover both the definition given in standard texts and the possibilities currently being investigated? Dbfirs 21:47, 8 April 2010 (UTC)
(outdent) -- As I understand it, all eukaryotic cilia and flagella are undulipodia. Thus, this would mean motile cilia and flagella, which wiggle, and primary cilia, which do not, but rather are a sort of cellular antenna. So the current definition is too limiting, it seems to me. N2e 04:24, 9 April 2010 (UTC)
... so should we have "including" rather than "typically" before our mention of uses? That would conform to definitions in standard texts and also allow the extension that you suggest. Dbfirs 06:40, 9 April 2010 (UTC)
Okay, I may have been wrong in thinking that primary cilia (immotile cilia) are included in undulipodia by the biological folks. Per this paragraph, directly from a medical source:
"Inside cilia and flagella is a microtubule-based cytoskeleton called the axoneme. The axoneme of primary cilia typically has a ring of nine outer microtubule doublets (called a 9+0 axoneme), and the axoneme of a motile cilium has two central microtubule doublets in addition to the nine outer doublets (called a 9+2 axoneme). The axonemal cytoskeleton acts as a scaffolding for various protein complexes and provides binding sites for molecular motor proteins such as kinesin II, that help carry proteins up and down the microtubules." That is from the Howard Hughes Medical Institute's HHMI Bulletin, The Importance of Being Cilia by Mary Beth Gardiner, vol. 18, issue 2, Sept. 2005, link here.
I'd like someone else to read this and see what you think. N2e 18:16, 9 April 2010 (UTC)