Erythalassa trygonina, the trident cuttlefish, is a species of cuttlefish in the monotypic genus Erythalassa from the Red Sea and the western Indian Ocean. They are also a major source of food for larger marine life like dolphins, seals, and seabirds.

It is characterized by 10 appendages consisting of two tentacles and eight arms that surround the mouth, which are covered in suckers. The difference between arms and tentacle clubs are that tentacles are an elongated arm that ends in a point, while tentacle clubs are a long appendage that has a rounded end. On its tentacle clubs, it has 8 different suckers in distinct rows and then 5 larger sized ones. Some of the arms have a hollowed-out section that replaces suckers. Their legs are placed below their eyes and are held together like a swimming keel. They also have free fins on their head, which are used to maneuver the cuttlefish in the water in whichever way they choose. They are able to propel themselves through the water by pumping water through and out of a siphon in their body. The eyes are covered with a transparent membrane and false eye lids.