Richard Goldberg posted an interesting observation on his Facebook page; see his video here: http://on.fb.me/Yf3LC5
He wrote “One of the truly bizarre behaviors of Annulariid snails is hanging by a single silken-like thread, presumably as a way to protect itself while aestivating. It was once thought that these snails were trapped by a silken thread from a spider, but it was concluded from further observations that it was in fact the snail that created the thread. From my own observations made over the past few years in Jamaica, I found that this behavior may in fact be an opportunity for the snail to expand its shell while being removed from the substrate [and predators] that would impinged its growth. The snail in the first clip was actually adding to its shell while I shot the footage. I shot the three clips in the compilation at night in December at two locations. The species here is Parachondria (Parachondrops) sauliae (Sowerby I, 1843), a 10 to 12mm species known only from the central limestone forests of the island. I have observed at least 6 other species of Jamaican Annularids doing the same thing, all at night time.”.
In the thread on his page, Tom Watters remarked “What is interesting (to me at least) is that annulariids from Curacao also suspend themselves. The difference is that the Curacao species use numerous short threads rather than one long one. A deeply rooted ancestral trait?”.
Interesting and food for thought. Of course, more observations would be needed for this hypothesis to be tested.