This is an Umbrella Octopus

When resting at the floor, the octopus's behavior falls into one of two tactics: bottom-resting or flat-spreading. Bottom-resting is when the octopus is resting near the floor. It will erect its mantle, curve the outer edges of its tentacles inwards to have them be the only part making contact with the floor. The fins are extended out parallel to the bottom to maintain balance. When flat-spreading they spread their tentacles and web, so it is parallel to the bottom and they keep the edges of their tentacles curved inwards. Their heads will point backwards at a small angle and their fins will be used for stabilization.