Natefrog described it pretty well. Most loricaridae have interopercular odontodes (try saying that after a few pints
![Wink ;-)](./images/smilies/icon/wink.gif)
. They do have a function: They are used as a defence mechanism against anything that may be seen as a threat, for instance in territorial fights or when some other fish is trying to steal their food.
In some species, males have more defined odontodes, in other cases the males and females are pretty much similar.
Also, a pleco in a bag will use these odontodes to puncture the bag by squeezing it's head into a corner and flaring the odontodes against the bag. The shop I go to tape the corners to avoid the pleco getting in there.
--
Mats