Behold the beautiful and otherworldly Blanket Octopus. Like the Argonauts (to which they are closely related), they live near the ocean’s surface, and can be found in both tropical and subtropical waters. There are four known species (the one depicted here is apparently T. gracilis, aka the Palmate Octopus), all of which share the same astounding anatomical and behavioral traits unique to this genus. Let’s begin with the name. As should be obvious from the image above, the female Blanket Octopus has two arms (the dorsal and dorsolateral, if you want to get technical about it) which are significantly longer than the rest and are connected to two other arms by a massive sheet-like membrane (the webbing is absent from the other four arms). It seems this “blanket” is unfurled when the animal feels threatened, presumably to make it appear bigger to any potential predator. Young individuals practice an altogether different defensive strategy. Apparently immune to the venom, they have been observed to carry pieces of the stinging tentacles of the Portuguese Man o’ War. The Blanket Octopus also exhibits one of the most extreme examples of sexual dimorphism of any animal: males, at 2.4 cm (or smaller), are minute, while the females can exceed 2 m in length.