Phylum Cnidaria (Cnidarians)

Phylum Cnidaria (Cnidarians)

Biology 11Name: ______

Phylum Cnidaria (Cnidarians)

Ref: Heath 453-456

A. Introduction

•most cnidarians are found in ______environments, but some live in fresh water (eg. Hydra)

•phylum Cnidaria gets its name from the stinging cell (cnidocyte) that is found all members

•the cnidocyte contains a stinging structure called a ______

•all cnidarians are ______-bodied animals with stinging ______arranged around their mouth

B. Body Forms: Polyp and Medusa

•both forms consist of two cell layers (ectoderm or epidermis and endoderm or gastroderm) separated by a jellylike material (______)

•To do:

•label the body forms below as either polyp or medusa

•also label theepidermis, gastroderm, mesogleagastrovascular cavity, cnidocyte nematocyst,tentacles, mouth/anus, body stalk (for polyp)

•indicate whether the form ismotile or sessile

•cnidarians are classified according to which stage (polyp or medusa) predominates in the life cycle (some cnidarians have an alternation of generations type of life cycle where a polyp stage alternates with a ______stage)

•examples of cnidarians in which polyp stage predominates:

•examples of cnidarians in which medusa stage predominates:

C. Reproduction: Life Cycle of Jellyfish Aurelia (simplified version)

Label the following structures: medusa, polyp, egg, sperm, blastula, planula

1.What is the planula? ______

2.What are the two body forms of the jellyfish shown in the diagram?


3.What kind of symmetry does Aurelia have? ______

4.Where does meiosis occur in the jellyfish life cycle? ______

5.What happens between fertilization and the planula stage of the jellyfish?



6.Is the production of medusae from the polyp shown in the life cycle an example of sexual or asexual reproduction? Explain your answer. ______



7.What are the structures that aid mobility of the planula called? ______

8.Describe how a medusa moves through the water. ______



9.How is the planula like the larva of a sponge? ______


D. Structure of Hydra

•Label the following structures: Gastrovascular cavity,Tentacle,Cnidocyte,Ectoderm, Endoderm,Mesoglea,Ovary/Teste,Bud,Nematocyst,Mouth,Basal Disk

hydra drawing

E. Form and Function in Cnidarians

1.Feeding and Digestion

•______located on tentacles release barbs containing ______to paralyze or kill prely

•______push food through ______& into ______

•specialized cells in the gastroderm (endoderm) release ______that partially digest food

•food fragments taken up by gastroderm cells (via ______) & further digestion takes place inside cells (______cellular digestion)

•nutrients transported throughout body by ______

•undigested wastes are expelled through ______(therefore ______body plant)

Symbiotic Relationships (describe how many cnidarians are dependent on photosynthetic symbionts)

2.Gas Exchange, Excretion, Internal Transport

•no specialized systems are necessary because

3.Nervous System

•cnidarians lack a ______nervous system & ______

•have simple nerve ______that coordinates movement of ______& body

•nerve ______is concentrated around the ______& is found throughout ______

•specialized ______cells in epidermis detect ______in food & ______

•movement is accomplished by ______cells that contract under ______stimulation


•most cnidarians reproduce ______& ______

•asexual is via ______(describe process)

•sexual (describe usual process)

•some exhibit ______of generations between ______& ______stages (although both are ____ n ______)