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What’s
That?
Photographer: Nandakumar M. N.
Location: Lembeh Island, Sulawesi, Indonesia
Details: Camera: Canon 5DsR, Lens: Canon 100 mm. Macro,
Shutter speed: 1/125 sec, Aperture: f/18, ISO: 125, Focal length: 100 mm.
Image taken: October 23, 2017; Time: 10.00 am.Look closely, and you will see two magnifi cent marine
creatures in the foreground of this photograph. One, a
brightly-coloured sea slug known as the nudibranch, a redline
fl abellina Flabellina rubrolineata to be precise, which can be
seen grazing on an even more bizarre looking animal – a blue
club tunicate Rhopalaea crassa. Their incredible, seemingly
fl uorescent colours make for a heavenly spectacle.
Nudibranchs are essentially marine molluscs that shed their
shells once they outgrow the larval stage. But the absence of
a shell is more than compensated by the presence of feathery
tentacles known as cerata, which are armed with stinging cells
or toxin-producing nematocysts, acquired from their cnidarian
prey, to deter predators. While the nudibranch is motile,
the tunicate is sessile, which means it remains latched on to
substrate such as rocks or coral reefs for its entire adult life.
The tunicate larva, however, is mobile and searches for a good
substrate to settle on until metamorphosis relieves it of its
chordate characteristics such as the tail.Being stationary leaves one vulnerable to predators
and so nature has armed the tunicate with the ability to
contract and squirt out water on alien touch. That’s why it
is also known as the sea squirt. Interestingly, the tunicate
gets its name from the extracellular sheath or ‘tunic’ that
envelops the animal. In the case of this glassy, cup-shaped
blue club tunicate, the ‘tunic’ almost lends the animal a
halo-like illuminance.
Together, the two marine animals embody the
utterly diverse and beautiful living world that makes up
the ocean. s