Sloppy semantics on my part are the source of some of the questions posted here. Here's some clarification: First, by "escaped" i used a euphemism that generally means purposely introduced or gone feral from some ill-advised introduction -- aquatic snails rarely "escape" like the family parakeet does. Both are the case with Marisa. It is certainly a common aquarium species, and undoubtedly was dumped at some time or another into these river systems, along with Melanoides and Tarebia, for which we have no other viable explanation for their presence, and several "Tropical Fish" species which also inhabit these springs and headwaters (putting even more things at risk). Marisa was also introduced as an aggressive herbivore in hopes that it would control the also purposely introduced and now invasive Water Hyacinth, which it has failed to do of course. The greater threat from these snails in this system is that they may be a direct threat to Texas Wild-rice, an endangered endemic known only from the springs. If they are a threat to the endemic Elimia, it is indeed from "crowding out" so to speak, from the consumption of native plants, resulting in out/overcompetition. The trumpet snail Melanoides is even more threatening in this regard, as it may be so abundant as to seem to hardly leave space for other invertebrates. In my original post i said "may be" a threat and that was purposeful wording, as we haven't proof yet, though it is widely hypothesized. Just a few months ago i did a sample sweep in the Comal and came up with 596 Melanoides, 2 Tarebia, 2 Marisa and 3 Elimia. Elimia has certainly declined but it is still holding on, and thought to be stable -- it probably also benefits somewhat from management designed to protect the other endemics there (for which i also failed to mention Salamanders as endangered). Marisa is more localized in its abundance that Melanoides in my experience -- while Melanoides is common throughout the upper springs area, Marisa may be abundant in a 25 foot stretch and then almost absent 50 feet away. All the invasive snails are apparently limited by a low tolerance for cold, and are not found systemwide. Secondly, on the extinction list, i was probably sloppily bold in saying "this" was a list of 387 recently "extinct" species. I was merely passing on a website i found while trying to look for answers to questions posted here about Lottia. This list, by the way, is repeated in various forms across the net -- the one i posted here i believe is the original compilation (and my "trust" in it certainly had something to do with the imprimatur of the AMNH). I too have problems with individual species on the list. I suspect that certain minimal criteria were used for adding forms to the list, they were done by "committee", and not much follow up research to determine actual status was done. There are likewise some problematical listings at USFWS and in CITES that probably are of the same ilk. The list IS advertised as a beginning and fairly begs for corrective input. Putting the word out on forums like this may be one of the better ways to begin correcting inappropriate listings as workers more familiar with local situations become aware and post their own findings and impressions, so that we all can bring attention to problems as they occur. blue austin, texas _________________________________________________________________ Click here for a FREE online computer virus scan from McAfee. http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963