Kingdom
Animalia
Phylum Cnidaria
Characteristics
 Radial
or biradial symmetry
 Diploblastic organization
 Mesoglea between epidermis and
gastrodermis
 Gastrovascular cavity
 Nerve net
 Cnidocytes – used in defense and
feeding
Reproduction/Life Cycle
 Can
be monoecious or dioecious
 Alternate generations between
polyp and medusa form
 Polyp – asexual and sessile
 Medusa – dioecious and free
swimming
Reproduction Cont’d
 Planula
– Cnidaria larvae
 Polyps are produced by budding or
planula
 Medusae formed by budding from
a polyp body wall
Feeding
 Use
cnidocytes to stun or kill prey
 Tentacles contract to bring food to
mouth
 Food is digested in gastrovascular
cavity
Support and Locomotion
 Hydrostatic
Skeleton
 Some classes have longitudinal
muscles that aid in movement
 Polyps – somersault, inchworm,
glide on base, and walk on their
tentacles
 Medusae – swim and float
Classification
Class
Hydrozoa
Class Scyphozoa
Class Cubozoa
Class Anthozoa
Class Hydrozoa
 Mostly
marine, but the only class
with freshwater members!
 Alternate generations
 Mostly colonial polyps
Obelia
 Gastrozooid
– feeding polyp formed
from planula larvae
 Grows through budding into more
gastrozooids
 Gonozooid – reproductive polyp that
forms medusa by budding
 Medusae then reproduce sexually
Gastrozooid
Gonozooid
Gonionemus
 Medusa
predominant
 Has a velum (shelf-like lip that
projects inward)
 Velum creates jet propulsion
 Mouth at end of a manubrium
 Nerve ring that coordinates
swimming movements
 Statocyst – responds to gravity
Hydra
 Freshwater
 Polyps
only, no
medusae
 Testes form
sperm by
meiosis
 Ovaries form
one egg each
Physalia
Portuguese man-ofwar
 Colonial
 Cannot swim
 Cnidocytes in
tentacles are lethal to
small vertebrates and
dangerous to humans

Class Scyphozoa
 All
marine
 “True Jellyfish” – medusa
dominant
Stinging Nettle, Mastigias
Aurelia
 Gastrodermal
cells have cilia to
circulate food
 Feeds on plankton
 Rhopalia – chemoreceptors
 Lappets – touch receptors
 Statocysts – gravity sensors
 Ocelli - photoreceptors
Class Cubozoa
Medusae are
cuboidal
 Polyps are
reduced or
absent
 Tentacles hang
from corners

Class Anthozoa
 Polyps
only, no medusae
 Mouth has a pharynx
 Gastrovascular cavity is divided
into sections
 Sexual and asexual reproduction
Sea Anemones
Corals