Original function of gills in bivalvia

[ManBearPig89]

Hi!

Im working on my zoology- paper and got this question regarding bivalvia, and i can't find a solution to the problem. The function of the originall gill, or umh, the "pre -gill" if you like.

I know that apart from the uptake of 02/ descretion of gases, the gills also work as a mecanism to trap food.

I don't know if this might be the function of the "pre- gill", or if it's something else. I considerd the function might have something to do with "cleaning", but I can't think of anything else right now.

Thoughts?

[Darby]

So what might be the ancestor of the bivalves - would it have most likely used a gill for one or the other of those functions?

[ManBearPig89]

I red on wikipedia that it was difficult to pinpoint the ancestor of bivalvia do to big gaps in the foissil record.
Later, i red (here http://www.sciencemag.org/cgi/content/a ... 6/4161/311) that some molluscan might be filter- feeders in early cambrian.

Do you think the filers later would develop into gills? I think it might be possible, given the "filer like" strukture of gills...

[Darby]

Well, would it be easier to be a surface feeder with gills for respiration, or a filter feeder with no way to breathe?