its called a garden eel (Taenioconger hassi) here is some info...
The Garden Eel, also known as Hass's Garden Eel, looks like a colony of seagrass.
The main portion of the Garden eel is usually buried in the sand, and if approached, retreats into the substrate. Several of these eels may be kept together in a 100 gallon or larger aquarium with at least 6 inches of sand, a gentle current, and without aggressive tank mates. Decor should be kept at a minimum. A tight-fitting lid is required to prevent escape.
The Garden Eel diet consists of meaty foods and live foods such as freshwater ghost shrimp or small feeder fish.