Phylum Cnidaria

Classification

• Class Scyphozoa – Jellyfish

• Class Anthozoa – Sea Anemones & Corals

• Class Hydrozoa - Hydra

General Characteristics

• Stinging tentacles

– Arranged in ring around mouth

• Saclike digestive tract

• Radial symmetry

• Nerve net

– One part stimulated, all parts respond

Class Scyphozoa—the jellies

Class Scyphozoa

• Medusa and polyp body forms

• Body composed of epidermis, mesoglea,

& gastrodermis

• Considered plankton

• Limited locomotion

– Contraction of muscular ring around medusa

• Gas exchange occurs by diffusion

Sea Nettles Video

Monterey Bay Aquarium

Feeding

• Tentacles covered in stinging cells called cnidoblasts– Contain nematocysts

• Coiled threaded with barbs

• Discharged when mechanically and chemically triggered

• Most barbs contain paralyzing toxin

• Once discharged, cannot be reused

– Tentacles pull food to mouth

– Food enters gastrovascular cavity

– Enzymes secreted; extra and intracellular

– Waste expelled out mouth

Feeding (cont.)

• Sticky mucus on medusa also used to

catch food

– Food sticks to surface

– Ciliated cells move it to the mouth

Moon jelly

The moon jelly has one of the weakest

stings of any jellyfish. These jellies trap

much of their food on the sticky mucus

covering their bell, then transport it to

their tentacle

• sexual and asexual phases

Lion's Mane jelly

Not only the largest of all jellies but with tentacles that can reach over 100 feet, the lion's mane jelly is the longestanimal on earth! Not all reach this size but even the small ones pack a powerful sting!

Crystal jelly

These seemingly harmless

creatures can open their mouths

wide enough to swallow jellies

half their size. They light up

when disturbed. People harvest

them for the chemicals that

make them glow.

7 ft.

120 ft.

Box Jelly (Sea Wasp)

Found in shallow waters of

N. Australia during summer

months of Oct.- Aug.

5 to 25 cm across, with four

groups of up to 15 tentacles.

Venom from a single

creature can kill up to 60

adults. Get stung by one

and you have from 30 sec. to

4 min. to get help or die!

Class Anthozoa—Sea Anemones &

Corals

Adult polyp stage only

• Sessile (limited

movement)

Sea Anemone

• Some symbiotic relationships--mutualism

– Sea anemone and clown fish

– Coral and algae

Life cycle

• Asexually

– Some split in half

– Regenerate base pieces

– Budding

• Sexually

– External fertilization in water

– Internal fertilization

• Sperm released out of males mouth

• Enters female and absorbed into ovary

• Larvae released into water by female

zooxanthalle algae

Class Hydrozoa• Hydroids

• Intertidal and subtidal areas

• Some independent

• Some colonial - many polyps working together as a single organism

• Can also have medusa forms, although polyp form is dominant

• Some grow on and coat other ocean animals

Hydractinia echinata Hydra oligactis Portuguese Man-of-War

Portuguese Man-of-War

• Hydroid colony

• Tentacles with stinging cells several meters

• Four different polyps make up organism

– The float (pneumatophore) is a single individual

and supports the rest of the colony.

– The tentacles (dactylozooids) are polyps

concerned with the detection and capture of food

– Digestive polyps (gastrozooids) break down the

food.

– Reproduction is carried out by the gonozooids.

Portuguese Man-O-War

are eaten by sea turtles

(loggerheads and

leatherbacks), and some

fish have symbiotic

relationships with the

Man-O-War, living among

the tentacles

Obelia

• Polyp colonies

• Dominant asexual

polyp stage, but also

has medusa stage

Phylum Ctenophora(sometimes confused with Jellyfish)

• Comb jellies

• 8 rows of fused cili (combs) for movement

and feeding

• One species has nematocysts on

tentacles

• Float near surface

• Bioluminescent

Sea Gooseberry

When is a jelly not a jelly at all? When it is a comb

jelly. Comb jellies are ctenophores, with rows of

iridescent combs instead of stinging tentacles.

Gooseberries also have two long tentacles for

capturing prey.

Comb Jelly