This Flamboyant Cuttlefish - Metasepia pfefferi is small in size, around 6cm and is likely already adult.
They are most likely the most colourful/beautiful of all Cuttlefishes, with the ability to change its colours especieally to bright yellow with pink and as they move around on the sandy bottom, they flashes colours from the head to the tail.
This is a picture of the same Flamboyant Cuttlefish, resting on the sandy bottom :
"Metasepia pfefferi", also known as the flamboyant cuttlefish, is a species of cuttlefish occurring in tropical Indo-Pacific waters off northern Australia, southern New Guinea, as well as numerous islands of the Philippines, Indonesia and Malaysia. The flesh of this colorful cephalopod contains unique acids, making it unsuitable for consumption.