Page 162 - Atlas Of The World's Strangest Animals

162 ATLAS OF THE WORLD’S STRANGEST ANIMALS

Jellyfish reproduction is far from straightforward, although it After fertilization has taken place, the female releases
begins, naturally enough,with the male’s sperm fertilizing the tiny larvae, known as planulae,which come to rest in
female’s eggs. shallow water.

In the world of jellies, mating isn’t merely a matter of boy When you spend your life roaming the oceans, it can be
meets girl. It’s more a case of boy becomes girl! hard to find a partner, but luckily compasses don’t need to
Scientifically speaking, adult compass jellyfish are meet to mate. Males simply release their sperm into the
considered to be protandrous sequential hermaphrodites, water and this fertilizes any suitable eggs it encounters.
which means that they function initially as males and then, Fertilization takes place inside the female and she releases
later in their lives, become females. It sounds curious, but free-swimming larvae (known as planulae) during the
this does have its advantages. summer or autumn. Planulae are tiny, with flattened
bodies in which both halves are mirror images – a
condition known as bilateral symmetry.
Compass jellyfish habitats These ‘jelly babies’ settle onto the sea bed or attach
themselves to any safe, secluded surface.There, within a few
days, they develop into scyphistoma. In this form, they are
sessile – they are not able to move around – but rely on their
tentacles to grab passing plankton in order to eat. Depending
on how well they have fed, the scyphistoma may be ready to
reproduce themselves by the following spring.The upper
part of these marvellous creatures then divides to produce
flower-shaped embryos (called ephyrae), which float away to
begin lives of their own.This second-stage reproduction is
asexual, as opposed to sexual reproduction, which involves
the combination of male gametes, called sperm, and female
gametes called eggs or ova.
These miniature jellyfish may take up to two years to
develop into fully mature adults (known as medusas), and
then the whole wonderfully strange process is ready to
begin all over again.

Hydraulic hunters
Jellies don’t waste energy chasing down prey.They let time
and the tides do the job for them.This doesn’t mean that

(c) 2011 Marshall Cavendish. All Rights Reserved.