Sub Pens, Boca Chica Key, Florida, 15 feet

Fluorescent image

Locally abundant on silty bottom of quiet lagoons in association with Red Mangroves.  Will release powerful nematocysts into the water with the slightest disturbance.  Contains zooxanthellae and lays upside-down to expose tentacles to the sun.  Settlement requires chemical compounds released by rotting Red Mangrove leaves.  Attains 12 inches.  Tropical Western Atlantic.