The size of a very small fish scale, equally as
flat and even more transparent, there is an open ocean, mind-blowing,
male, modified copepod called Sapphirina that has caught
the eye of many a holidaymaking snorkeller in the tropics.
Put on a face mask, leap off your luxury launch,
hang at the surface and look down into deep blue waters and ten
to one you'll catch a glimpse of a little flash of iridescence
now and again. The perpetrator is a copepod, not very copepod-like,
but none the less related to the "cattle-of-the-sea" - that huge
group of bewhiskered crustaceans that are the staple diet of many
a fish and many a whale.
More precisely it is a male copepod of the genus
Sapphirina, whose female is strikingly dissimilar. Her
mate is totally transparent and very flat and lives inside transparent
salps which he parasitizes. So how come the iridescent colour?
If a beam of light (sunlight works well!) is directed at a certain
critical angle at the surface of this diminutive character, the
white light is prismatically split into some of the most distinctive
colours in the spectrum. Polygonal stacks of transparent chitinized
plates adorn the segments of this woodlouse-shaped copepod and
they split the light by diffraction and refraction. No two individuals
are the same and it is now believed by some researchers that the
phenomenon is used in communication.
For me though "opal" describes the shifting colours
better than "sapphire" - but then we'd have to call it "Opalina"
and that name is already booked!
This article was written
by Peter Parks
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