14 February 2011

Preliminary notes for a planned talk on Rissooidea

At the MAM meeting in March I intend to give a short talk about on species of semi-terrestrial snails in the superfamily Rissooidea. The main topic will be the anatomy of respiration in the subject species, but I haven't yet gone that far. Today I started preparing an outline of what I think I will mention. Here is what I have so far.

The superfamily Rissooidea comprises several families of aquatic and semi-terrestrial snails. The member species are small, operculated and gilled.

Not sure what other anatomical and conchological characteristics they share.

Bouchet & Rocroi (2005) included 23 extant families.

I will discuss 3 species in 3 families:

Assiminea succinea (Assimineidae)

Pomatiopsis lapidaria (Pomatiopsidae)

Truncatella caribaeensis (Truncatellidae)

Before we go further, a short diversion: What does it take an aquatic snail to become a terrestrial snail?

—Ability to exchange respiratory gases with the air.
—Ability to withstand moderate water loss.
No big deal for many intertidal species. Example: Batillaria minima.
—Ability to reproduce outside of water.
Requires direct development (suppression of free-swimming or planktonic veliger stage) and direct transfer of sperm (or spermatophore).
—Ability to keep tentacles erect in the air. This may be an optional requirement, but I am not sure.

Respiration in aquatic gilled snails.

Gills versus lungs
Respiration (gas exchange between blood and an outside medium—air or water) always takes place across a wet membrane whether the organ is a gill or a lung.
A gill, because it is usually a branched or a filamentous structure, provides a large surface area for gas exchange. A gill is not necessarily restricted to an aquatic medium: if it can stay erect, it will also function in the air.

This is still very incomplete and is subject to change. Expect a revised outline during the next several weeks.

1 comment:

Anonymous said...

Very cool subject material Aydin. If I can't attend MAM then I can at least read your outline instead, or maybe you will post the presentation online somewhere after the event.

Susan J. Hewitt