25 August 2008

Snail dissection in progress: Oxyloma retusa

I have dissected several specimens of the land snail Oxyloma retusa and figured out the make-up and the arrangement of the components of their genitalia. But at the moment I am a bit confused about the relation of the retractor muscle of the right tentacle with the genitalia.

I normally take photographs, but last nite I had time only for a freehand drawing. Although I am not very good at it, drawings are useful–if they make sense later–to establish a quick record of whatever one is observing.

OxylomaDrawing

In most pulmonates, the retractor muscle of the right tentacle passes between the penis and the vagina. Why is it there and not out of the way, say, underneath the genitalia? That's because evolution doesn't work with pre-planned designs and is not concerned with neatness. Whatever works stays around even if it's a bit awkward.

To those of you who are not familiar with the complicated genitalia of pulmonates the above drawing will not mean much. Just find the arrow labeled "retractor of right tentacle" and then notice that the darker colored retractor passes between the vagina on the left and the penis on the right (remember, they are hermaphrodites). What is confusing me is the branch of the retractor that I drew in green. That branch seems to insert to the base of the vagina and I don't remember noticing that in other species of pulmonates I have dissected. I will examine this particular dissection again later tonite and try to sort things out. I will also take pictures.

I will end with a disclaimer: This is a work in progress and my interpretations presented here are subject to change. Use them at your own risk!

Part 2 is here.

2 comments:

Kevin Zelnio said...

Is this common in the O. restusa you are examining? Or an isolated individual? Could it be an artifact of preservation? For instance, as you know, ethanol can distort things, especially if you are looking at thin sections. I assume you are looking at it whole though right? Do sister species, or other members of the genus have the same anatomical feature?

AYDIN ÖRSTAN said...

Yes, it's the whole thing & there is no distortion. But I was slightly mistaken about where that "green" branch was going. I took some good pictures, but don't have time to prepare them now. I'll post them tomorrow evening.