Despite its name suggesting that it’s a reptile, the Basilosaurus is actually an ancestor … It habitats in deep sea … Basilosaurus. Distinct Feature: Long, … Fin WhaleSize: 100,000 pounds, 68 feet. Diet: Plankton. Largest sea creatures – Giant Isopod: with a maximum weight and length of approximately 1.7 kilograms (3.7 lb) and 76 centimetres (30 in) respectively. Genus: Balaenoptera. The Giant Isopods are deep sea creatures that look like some monster out of an Alien movie. 20.