Yesterday's post was about the removal of the shell of a Truncatella caribaeensis specimen in preparation for dissection. The subsequent dissection went well and I was able to see what I wanted to see.
Here is the dissected snail after the mantle was cut open and moved aside.
The white, folded organ labeled "penis" is, well, the penis of the snail. It is about a half of the spiraled body length of the snail (talk about penis enlargement).
What interested me more was the row of tiny white flaps to the left of the penis. They constitute the ctenidium or the gill of Truncatella caribaeensis. Here is a larger view.
This snail spends its entire life cycle on land very close to the sea, but out of it, unless it is carried away by the waves or the tides, and because of that it is considered a land snail. But it still, as we see here, retains the gill of its aquatic ancestors from whom it evolved. On the other hand, there are other species of snails that live on land alongside Truncatella, for example, Melampus bullaoides, that lost their gills a long time ago and obtain their oxygen thru their vascularized mantle, or "lung." But they nevertheless return to the sea to reproduce, because they still have planktonic larvae as did their ancestors.
Evolution works in mysterious ways.