Sea menaces are aquatic predators native to Thanatos. They are mammalian, but are nothing like Terran sea mammals, as this page will explain.
Sea menaces are truly strange looking. Their heads look more like that of a frog than any mammal, with a single 50 cm long tentacle coming from the side of each lip. Their mouths are filled with sharp, serrated teeth, looking more like tiger shark teeth than cetacean teeth. Their eyes are huge and bulging, with split pupils. The torso is long, cylindrical and has 4 dorsal fins, each of which look like shark fins. At the end of a long, thin tail is a fluke. Only the front limbs are present, looking like the flippers of a sea turtle. The hide is covered in a coat of grey fur on the back, with hard, orange scales on the stomach. Sea menaces are 15 feet long, and weigh up to half a ton.
Sea menaces eat most things smaller than themselves, especially young algaeworms and small fish. However, they are themselves prey for many creatures, including young tusked leviathans.