Eye opener

Focus-Science and Technology - - CONTENTS - TONY WU/NATUREPL.COM

Mind-blow­ing images from Earth and be­yond.

FALSE BAY, SOUTH AFRICA

Th­ese two oth­er­worldly crea­tures are preda­tor and prey. On the left: the blue sea slug. On the right: the deadly ten­ta­cle of the Indo-Pa­cific Por­tuguese man o’ war.

Both were washed ashore as part of a mass strand­ing of man o’ wars in South Africa. The Indo-Pa­cific Por­tuguese man o’ war is a ruthless killer, us­ing its sin­gle, long ten­ta­cle to stun and cap­ture its prey. But the sea slug is more than a match. Not only does this tiny (3cm-long) nudi­branch feed on man o’ wars, but it also steals their poi­son. The sea slug is im­mune to the man o’ wars sting­ing cells (ne­ma­to­cysts), so it con­sumes them and stores them in the tips of its im­pres­sive ten­drils, or ‘cer­ata’, where they help to de­fend against other foes.

The sea slug is also very well cam­ou­flaged. Its blue side faces up­wards, blend­ing in with the ocean when seen by seabirds from above, while its sil­very-grey side faces down­wards, help­ing it to merge with the ocean sur­face when the slug is seen from be­low.

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