This part of the aquifer is found near the region around San Antonio and is characterized by deeper and warmer waters (25oC) as well as lower numbers and biodiversity of invertebrates. Where the aquifer is shallower with well depths of about 100 meters, the temperature is cooler around 21°C. This cooler aquifer region has more biodiversity of invertebrates. Deeper in the aquifer, at 500 meters, the temperature rises to 25°C.
Here, the top predator is the Texas Blind Catfish (S. eurystomus), which has an enlarged brain to smell and hear better in dark environments. Adapted to life in total darkness, the catfish doesn’t have eyes or skin pigmentation. Compared to other catfish species, it has reduced muscle, skeleton and swim bladder. It has an enlarged head to compliment its big brain and large fat deposits which compensate for the limited food sources in the cave environment.