Illustrated here are lobster phyllosoma
larval stages, superfamily Palinuroidea. These particular individuals
were photographed off Lizard Island on the Great Barrier Reef,
Australia.
Among no group of marine animals
is metamorphosis more spectacular than many of the crustacea and
amongst them the most bizarre story comes from our old friend
the lobster, in particular the spiny lobster and slipper lobster.
From the eggs that the female carries beneath her abdomen, hatch
small and very flat, transparent and spindly larval phyllosomas,
literally 'leaf bodies'. So long-legged are these animals, with
their gawky stalked eyes (see above left), that they always seem
cumbersome and inept. In reality they are dead smart and should
take the prize for cooperative living and long distance hitch-hiking.
They have devoloped a really neat adaptation to assist with their
unique lifestyle. While existing as larvae in the plankton community
they attach to a jellyfish or hydromedusan by grabbing hold with
all four pairs of legs (see above centre). If the jellyfish begins
to drift the baby lobster cannot propel itself around because
all of its limbs are needed to hold on. Therefore, they have adapted
and developed a side branch to each limb that ends in a feathery
paddle which can be used independantly for movement (see above
left).
By the time the phyllosoma is over
a year old it may be five centimetres wide. Upon arrival in shallow
waters the larval lobster swims free and begins its metamorphosis
by discarding at least three quarters of its larval body. Curiously
the part of the larval phyllosoma that forms the first stage of
the difinitive but miniture adult lobster is the hind end. The
front end of the phyllosoma, complete with stalked eyes, fused
head and shoulder, as well as all the main limbs, remain as the
discarded preambulator, to drift away, twitching in the water
column until some predator snaps it up. The hind end settles out
into a very small, only half a centimetre across, transparent
yet perfectly formed lobster still drifting at the surface. Gradually
it will descend to the substrate to find shelter and protection
while its pigmentation develops to aid camouflage and it continues
to grow into an adult.
|