There’s very little angelic about Glaucus atlanticus, the blue angel sea slug
Blue it may be, but there’s little to suggest any angelic qualities to this exquisite sea slug, other than a propensity for floating across (or, in fact, just under) the water like an ocean-going will-o’-the wisp.
G. Atlanticus, which can reach 3cm in length, travels the oceans upside down, clinging to the water’s surface tension with the aid of a gas-filled sac in its stomach, and is largely camouflaged against the water with its blue undercarriage and white back. It has four other closely-related species, all of which are largely similar but spread throughout the Pacific and Indo-Pacific oceans
A more fitting description than ‘angel’ might be its alternative name ‘the blue dragon’, which not only reflects its reptilian shape but also a fiery ability to tackle other surface-dwelling ocean predators, including the notoriously venomous Portuguese man o’ war (Physalia physalis) and other stinging hydrozoans such as the by-the-wind-sailor (Velella velella), upon which it feeds.
Having made a meal of its prey, G. Atlanticus goes on to store the venom from the hydrozoan’s nematocysts (stinging cells) in its cerata (the pointed fronds that surround its body) and uses them to defend itself against predators.
Diminutive it may be, but – depending on what it had for lunch on any given day – G.Atlanticus can pack a punch, so should you come across one, make sure you give it a wide berth to avoid a nasty sting.
