Today’s Objectives: 3.4 Describe characteristics of this phylum Identify life functions of cnidarians Classify and give examples of phylum Cnidaria

Animals with stinging cells 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 – 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 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 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 - 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-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 Cubozoa Venom from one individual can kill 60 adults. Takes 30 seconds to 4 minutes to kill.

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