Distribution: Rare in the Solitary Islands Marine Park. Known from the tropical West Pacific, possible distribution throughout the Indo-West Pacific region. In Australia recorded from Rottnest Island in Western Australia, Lizard Island in Queensland, south to Cook Island in northern New South Wales

Ecological Notes: Subtidal rocky reef, thought to feed on Sinularia sp. soft corals. Depth to at least 18 m.

Additional Notes: Variable colour, grey-blue to fawn, with yellow tips to large bulbous cerata, oral tentacles and rhinophores, also yellow edge to foot. Thought to obtain zooxanthellae from its food source soft coral, will voluntarily cast off cerata if disturbed or threatened, the autotomised parts providing a distraction for the predators. Grows to at least 130 mm, usually smaller.

References: Atlas of Living Australia website at https://bie.ala.org.au/search?q=Phyllodesmium+magnum, accessed 14/02/2021.

Australian Museum, Sea Slug Forum http://www.seaslugforum.net/showall/phylmagn, accessed 14/02/2021.