An open brain coral (Trachyphyllia geoffroyi) is a popular, brightly colored, large polyp stony (LPS) coral known for its fleshy tissue, folds, and ability to move around on the sandbed in an aquarium. 
It's considered relatively easy to care for, making it a good choice for beginners, and is characterized by its vibrant colors (greens, reds, yellows) and its habit of inflating during the day. 
Appearance and characteristics:
Shape: Resembles a brain with folds and valleys, often with a figure-eight or clover-leaf shape. 
Color: Comes in many colors, including neon green, red, pink, yellow, and brown. 
Movement: It's a free-living coral that can inflate its tissue and move to find better conditions, though this is limited in an aquarium. 
Polyp: Typically a single, large polyp that inflates to show its fleshy tissue and tentacles for feeding. 
Aquarium care
Placement: Place on the sandbed at the bottom of the tank, away from strong currents and intense lighting. 
Lighting: Moderate lighting (PAR 50-100) is sufficient, and it often glows under blue light. 
Water flow: Low to medium flow to keep detritus from settling on it. 
Feeding: Photosynthetic but benefits from target feeding with pellets or liquid food. Turn off flow during feeding to allow it to capture food. 
Water parameters: Keep parameters like calcium, alkalinity, and magnesium stable, with low nitrates and phosphates.