Download Today’s Objectives: 3.4

Today’s Objectives: 3.4
 Describe
characteristics of this
phylum
 Identify life functions of
cnidarians
 Classify and give examples of
phylum Cnidaria
Phylum Cnidaria
Animals with stinging cells
Characteristics of Cnidarians
 Radial
or biradial symmetry
 Tissue-level organization
 Mesoglea between epidermis and
gastrodermis
 Gastrovascular cavity
 Nerve net
 Cnidocytes
feeding
– used for defense or
Life Functions of Cnidarians
 Reproduction/life
cycle
– Can be monoecious or dioecious
– Alternate generations between
medusa and polyp form
 Feeding
– Use cnidocytes to stun or kill prey
– Can contract tentacles to bring to
mouth
– Digestion occurs in gastrovascular
cavity
Life Functions of Cnidarians
 Support
& locomotion
–Hydrostatic skeleton
–Some classes have longitudinal
muscles for movement
–Medusa move by contracting bell
or jet propulsion
–Some polyps can walk on
tentacles, contract, inchworm or
glide on pedal disks
Reproduction in Cnidarians
 Most
are dioecious
 Polyp can develop through budding
or from a free-swimming planula
larva
 Medusa almost always formed by
budding from a polyp body wall
Classification of Phylum
Cnidaria
Class
Hydrozoa
Class Scyphozoa
Class Cubozoa
Class Anthozoa
Class Hydrozoa
 Mostly
marine
 This is the only class with freshwater
members!
 Alternate generations
 Mostly colonial polyps
 Only have cnidocytes in epidermis
 Sperm & egg are released outside
body
 No amoeboid cells in mesoglea
Obelia
– 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
Gastrozooid
Gonozooid
Gonionemus
 Medusa
predominant - Dioecious
 Has a velum (not found in other
classes) which creates jet
propulsion
 Mouth at end of a manubrium
 Nerve ring in addition to nerve net
that coordinates swimming
movements
 Statocyst sensory structure that
responds to gravity
Hydra
Freshwater
 Polyp only, no
medusa
 Testes form
sperm through
meiosis
 Ovaries form one
egg each
 Young “buds”
from parent until
ready to survive
on its own, then it
drops off

Types of Locomotion in Hydra
Physalia
Portuguese man-ofwar
 Colonial
siphonophore
 Does not swim, float
moved by water and
wind
 Long dactylozooids
(tentacles) contain
cnidocytes and kill
prey.

Class Scyphozoa
 “True
Jellyfish” – polyp form
reduced or absent
 All marine
 No velum
 Mesoglea contain amoeboid cells
 Cnidocytes in gastrodermis and
epidermis
 Gametes form in gastrodermis
Stinging nettle, Mastigias
Aurelia
Extensively branched canal system
 Gastrodermal cells have cilia to
circulate food
 Feeds on plankton
 Rhopalium – chemosensors
 Statocyst – gravity sensors
 Lappets – touch receptors
 Ocelli – photoreceptors
 Planula develop into a scyphistoma
polyp

Aurelia
Life Cycle of Aurelia
Medusa is cuboidal
 Tentacles hang from
corners
 Polyps reduced or absent
 Ex. Sea wasp

Class
Cubozoa
Class Anthozoa
 No
medusae, polyp only
 Mouth has a pharynx
 Gastrovascular cavity is divided
into sections
 Mesoglea contains amoeboid
cells
 Sexual and asexual
reproduction
Body structure of Anthozoans
 Pedal
disk
 Oral disk
 Siphonoglyph – moves water
into gastrovascular cavity to
maintain hydrostatic pressure.
 Acontia – prevents live prey
from damaging gastrovascular
cavity.
Sea Anemones
Corals