WOW! What a find! Unfortunately, I'm not a paleontologist. Based on the surrounding rock, which appears to be limestone, it's a marine organism. To get a better identification, I suggest you contact the geology department at Rice University in Houston or the State Geology group at http://www.beg.utexas.edu/outreach/state-geological-survey in Austin. I'm betting that if you send your images to them, they will be able to identify your fossil. If you remember where you picked it up, that is also useful information for identification. Nice fossil! Good luck solving your puzzle.