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 CnidariansRadial or biradial symmetryTissue-level organizationMesoglea between epidermis and

gastrodermisGastrovascular cavityNerve netCnidocytes – used for defense or

feeding

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 CnidariansSupport & 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 dioeciousPolyp 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 HydrozoaClass ScyphozoaClass CubozoaClass Anthozoa

Class HydrozoaMostly marineThis is the only class with freshwater

members!Alternate generationsMostly colonial polypsOnly have cnidocytes in epidermisSperm & egg are released outside

bodyNo amoeboid cells in mesoglea

ObeliaGastrozooid – feeding polyp

formed from planula larvaeGrows through budding into more

gastrozooidsGonozooid – reproductive polyp

that forms medusa by budding Medusae then reproduce sexually

Gastrozooid

Gonozooid

GonionemusMedusa predominant - DioeciousHas 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-of-

war 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

Class Cubozoa

Medusa is cuboidal Tentacles hang from

corners Polyps reduced or absent Ex. Sea wasp

Class AnthozoaNo medusae, polyp onlyMouth has a pharynxGastrovascular cavity is divided

into sectionsMesoglea contains amoeboid

cellsSexual and asexual reproduction

Body structure of AnthozoansPedal diskOral diskSiphonoglyph – moves water

into gastrovascular cavity to maintain hydrostatic pressure.

Acontia – prevents live prey from damaging gastrovascular cavity.

Sea Anemones

Corals