The Upside-down
Jellyfish
Cassiopea sp.
Phylum Cnideria
Class Scyphozoa
 The upside-down jellyfish belongs to order Scyphozoa,
the “true jellyfish”.
 As most Scyphozoan jellyfish do, the upside-down
jellyfish has two life phases: the medusa form and the
bottom-dwelling polyp form.
 Scyphozoans exhibit both asexual and sexual
reproduction; usually asexual as a polyp through
budding or strobilation, and sexual as a medusa with
gametes.
Order Rhizostomeae
 The upside-down jellyfish belongs to order
Rhizostomeae.
 The jellyfish in this order, unlike others in Class
Scyphozoa, have no tentacles of structures on the edges
of their bell, but have 4 to 8 highly branched oral arms.
 It is also common for the organisms in this order to have
multiple mouths, one primary and many secondary, often
distributed all along the oral arms.
Common Name
The common name for
Cassiopea sp., the Upsidedown jellyfish, comes from
their tendencies to settle
upside-down on the ocean
floor in shallow, muddy water.
They are also sometimes
called Mangrove jellyfish
because they are often found
in mangroves.
The upside-down
jellyfish doesn’t look
like a typical
Scyphozoan jellyfish,
but more like an
Anthozoan, like a sea
anemone. This
appearance is
beneficial to the
jellyfishes survival.
Like most jellyfish, the upside-down jellyfish hunts for food and
wards off predators using stinging cells (nematocysts). These
nematocysts are used to feed on plankton and zooplankton.
The upsidedown jellyfish
release their
stinging cells in
a layer of mucus
that floats in the
water. Their
sting is not
harmful to
humans but can
cause an itchy
rash.
These jellyfish also
have multiple mouths.
They have a primary
mouth and then many
secondary mouths (up
to 40) located on their
arms to quickly
capture and eat food.
The upside-down
jellyfish is a filter
feeder and they use
pulsations of their bell
to bring in planktonic
food.
In addition to their nematocysts, the upside-down jellyfish gets most of
its nutrition from its symbiotic relationship with photosynthesizing
zooxanthellae that are housed in the bell of the jellyfish. This is why
these jellyfish spend their time upside-down on the bottom of the ocean
soaking up sunlight for their photosynthesizing golden algae. They
aren’t born with the symbiotic algae, but rather they acquire it
infectiously.
Life Cycle
 Sexual Reproduction: The
upside-down jellyfish starts its
life out as a free swimming
planula larvae, which they
remain until they are about 2
cm. Then they invert their bell
and land upside-down on the
ocean floor in shallow water.
 Like most jellyfish, they
alternate between polyp and
medusa stages. In the polyp
stage new jellyfish can be
produced asexually through
budding and strobilation.
The upside-down
jellyfish share a
relationship with a
family of crabs
called Dorippidae.
The crabs will put
the jellyfish onto
their back and
carry it around for
protection from
predators
although the
jellyfish doesn’t
seem to get
anything out of it.
Phylum Cnideria
Class Hydrozoa
 Some Hydrozoans are solitary and some
are colonial. Colonial Hydrozoans can get to
be very large and sometimes the specialized
individuals in the colony cannot survive
outside of the colony.
 The Portuguese man of war (Physalia
physalis) is an example of a colonial
Hydrozoan
Order Siphonophorae
 The Portuguese man-of-war
belongs to Order
Siphonophorae.
 Siphonophores are colonial
Hydrozoans and are generally
long, thin, transparent pelagic
floaters. Some
Siphonophores, like the
Portuguese man-of-war,
resemble Scyphozoan
jellyfish.
 Each zooid that makes up the
organism is an individual, but
they are so strongly integrated
that they cannot live on their
own.
 Some Siphonophores can
emit light
Physalia Physalis
Portuguese man-of-war
 The Portuguese man of
war lives at the surface of
the ocean. They float
using their gas-filled
pneumatophore and the
remainder of the
organism is submerged.
 Portuguese man of war
are usually found in more
tropical waters
 Portuguese man of war
are composed of four
different types of polyp.
 The pneumatophore
 Dactylozooid
(stinging/feeding)
 Gonozooid (reproductive)
 Gastrozooid (feeding)