Cnidarians Ctenophorans 1 CNIDARIANS Phylum Cnidaria About 9000

Cnidarians & Ctenophorans 1

CNIDARIANS

Phylum Cnidaria • About 9000 species • Most are marine (jellyfish, coral, sea anemones, Portuguese man-of war) • All have arm-like tentacles • Soft-bodied • Carnivorous

Cnidarian Characteristics • Radial symmetry • Hollow gut -Gastrovascular cavity has single opening (serves as both mouth and anus) • Two tissue layers • Outer epidermis and inner gastrodermis

Cnidarian Characteristics • Either tubular or bell shaped • Tentacles surround mouth • Only animal with cnidocytes (stinging cells) found in the tentacles • Nematocyst – coiled, harpoon-like stinger inside cnidocyte that shoots out

Cnidarian Characteristics • Cnidocytes contain poison to paralyze prey • Tentacles bring food into mouth • Inner gastrodermis secretes digestive juices into gastrovascular cavity which digests food and circulates nutrients

Extracellular Digestion Food digested outside of cells

Cnidocyte Coiled nematocyst

Nematocyst Barbed, threaded stinger capsule’s lid trigger nematocyst

Cnidarian Systems • Have a simple nerve net & sensory receptors • Hydrostatic skeleton: circular and longitudinal muscles help in directional movement & capturing prey • Also use jet propulsion

Cnidarian Systems • After digestion, nutrients are transported by diffusion • Excrete wastes through diffusion • Ocelli: eyespots made of cells that detect light

Cnidarian Systems • Reproduction can be sexual or asexual • Asexual: budding • Sexual: external fertilization • Separate sexes

mesoglea-filled bell tentacles Jellylike mesoglea between two cell layers supports cnidarian

Two Main Body Plans of Cnidarians UPRIGHT TENTACLES HANG DOWN epidermis Polyp mouth mesoglea gastrodermis Medusa Mesoglea THICK Mesoglea THIN

Cnidarian Diversity • Class Scyphozoans: Jellyfish • Class Anthozoans: Sea anemones Corals • Class Hydrozoans: Hydra • Class Cubozoa: Box Jellies

Cnidarian Diversity Coral polyps Sea Anemone Jellyfish Coral polyps

Anthozoans

Anthozoan Characteristics Sea Anemones §Brightly colored & Resemble flowers §Solitary polyps §Feed on invertebrates & fish Corals §Most are colonial §Build limestone case §Live as polyps in their case

Sea Anemones & Coral • Exist only as Polyps • Clownfish live • in anemone tentacles Corals build a limestone case which build up & form reefs ANEMONE CORAL

Distribution of Coral Reefs

Hydrozoans

Hydrozoans Hydra • Exist only as polyps • Reproduce by budding • Freshwater only • Form resistant zygotes when environment is bad Move by somersaulting with tentacles •

Hydra

Hydra Feeding

Food in Gastrovascular Cavity

Portuguese man-of-war • Colonial Hydrozoan • • • (not a single organism) Tentacles sting prey such as fish & humans Polyps in colony feed Has gas-filled air float

Hydrozoan Life Cycle Most hydrozoans alternate polyp and medusa forms, as in the life cycle of Obelia

Obelia Life Cycle (Hydrozoan) Larva called a planula reproductive polyp male medusa female medusa ovum sperm zygote feeding polyp forming planula Fig. 25 -15 a, p. 411

Cubozoans Box Jelly. Fish

Scyphozoans

Scyphozoan Characteristics Jellyfish • Medusa is dominant body form • Go through small polyp stage during life cycle Stinging tentacles May live close to shore or the open ocean • •

Some Jellyfish Show Luminescence

CTENOPHORANS

Ctenophoran Characteristics • Called comb jellies • All marine • Approximately 100 species • May be spherical, ovoid, or elongate in appearance Bioluminescent •

Ctenophoran Characteristics • Radial symmetry • Have eight plates of • • • fused cilia that resemble combs Move by beating cilia Most of the body is jelly-like mesoglea Body & tentacles covered with sticky mucus to catch prey

Comb Jelly Anatomy

Beating Cilia Ctenophore: Comb Jelly

Ctenophore 44

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