Cnidaria LS2014 Zoology lecture 4 October 2006 Winslow

Radiata

Radially symmetrical

Sessile, sedentary, or slow

Predatory

Tissue (or “tissue-organ”) level of organization

2 germ layers

Endoderm becomes gastrodermis

Ectoderm becomes epidermis

Mesoglea in between

Saclike body plan, oral & aboral ends

Extracellular digestion in gastrovascular cavity

Intracellular digestion in gastrodermis

Tentacles

Nerve net

Statocysts & ocelli

Phylum Cnidaria

Aquatic, mostly marine

Nematocysts in cnidocytes

Muscles for locomotion

Polyp & medusa

Asexual & sexual reproduction

Planula larva

Class Hydrozoa

Colonial, polymorphism, commensal or mutualistic symbioses

Hydra—basal disc, hypostome, mouth, tentacles, buds

Obelia

colonial polyps bud & produce medusae

medusae reproduce sexuallyàplanulaàpolyp colony

Physalia—Portuguese man-of-war

Hydrocorals

Class Scyphozoa—true jellyfish

Aurelia aurita—moon jellyfish

Planulaàpolyp stagesàmedusa buds offàreproduces sexuallyàplanula

Class Cubozoa—cube jellyfish

Tetramerous symmetry

Class Anthozoa

Sea anemones

Large polyps with many septa

Zooantharian corals (“true corals”, “stony corals”)

Polyps in cups within calcareous exoskeleton

Often colonial, gastrovascular cavities connected

Hexamerous symmetry—6 septa

Coral reefs

Mutualistic red algae

Warm, shallow seas

High diversity of animal & plant species

Threats to coral reefs

Hi nutrients from sewage and fertilizer

Overfishing of herbivorous fish

Pollution & disease

Global warming

Acid rain

Octocorallian corals—soft corals, sea pansies, sea pens, sea fans, gorgonian corals

Octomerous symmetry—8 septa, 8 tentacles

Phylum Ctenophora (comb jellies)

Ciliary comb plates for locomotion