Sci&Tech Writer Jade Matlock delves into the world of the most curious octopus in the tropical seas

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Images by Michael Vecchione , Clyde F.E. Roper , & Michael J. Sweeney

The blanket octopus, known scientifically as Tremoctupus spp, is the classification of four varieties octopus that are identifiable by the transparent webbing that connects their dorso and dorsolateral arms in female adults, earning them their common association with blankets. Their other limbs are considerably shorter and have no such webbing. They can be found occupying the shallow to mid-water depths of subtropical and tropical oceans.

As a species, they have the largest case of sexual size-dimorphism in any non-microscopic animal. The females can measure up to six feet and six inches in length, whereas the men grow to approximately three centimetres in length on average. Male blanket octopi were not discovered until one was seen in the Great Barrier Reef, Australia in 2003 – their drastic size difference from their female counterparts has left scientists baffled for decades. It is understood that the naming of the blanket octopus is derived entirely from the characteristics of the female, the male is said to share none of these characteristics.

They have the largest case of sexual size-dimorphism in any non-microscopic animal

Male blanket octopi are able to reproduce due to producing sperm through the detachment of a specialised arm, the hectocotylus, which is presented to the females for fertilisation. The arm is then kept in the female’s mantle cavity until it is needed, when it can be used to fertilise upwards of 10,000 eggs. 

The blanket octopus is one of the most confusing species of aquatic animal currently dwelling in the tropical oceans, with its mammoth difference in size providing entertainment to all who find it.