The Upside-down Jellyfish

Cassiopea sp.

Phylum CnideriaClass 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 RhizostomeaeThe 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 NameThe common name for

Cassiopea sp., the Upside-down 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.

The upside-down 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.

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.

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 CycleSexual 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 CnideriaClass 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 PhysalisPortuguese 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)