This document summarizes key characteristics of cnidarians. It describes their three classes - Hydrozoa, Scyphozoa, and Anthozoa. Cnidarians are radially symmetric and have specialized cells. They live in water and have tentacles covered in stinging nematocysts that help capture prey. They reproduce both sexually and asexually, and different classes display different forms like polyps or medusae and move via jet propulsion or crawling.

1. PHYLUM COELENTERATAPHYLUM COELENTERATA
(CNIDARIANS)(CNIDARIANS)
Pages 323- 325Pages 323- 325

2. 3 CLASSES OF3 CLASSES OF
COELENTERATESCOELENTERATES
• Hydrozoa – HydraHydrozoa – Hydra
• Scyphozoa – JellyfishScyphozoa – Jellyfish
Man of WarMan of War
• Anthozoa – CoralsAnthozoa – Corals
Sea AnemoneSea Anemone
Page 323 Figure 9Page 323 Figure 9

3. PHYSICALPHYSICAL
CHARACTERISTICSCHARACTERISTICS
1.1. Where do theyWhere do they livelive??
All live in water – most in salt water butAll live in water – most in salt water but
the hydra lives in fresh waterthe hydra lives in fresh water
2.2. SymmetrySymmetry – radial (see page 316)– radial (see page 316)
3.3. Body StructureBody Structure – is more complex than a– is more complex than a
sponge (therefore they can eat largersponge (therefore they can eat larger
animals)animals)

4. 4.4. Cellular Structure –Cellular Structure –
a.a. like alike a sacsac with one opening – mouth-like structure where foodwith one opening – mouth-like structure where food
enters and leaves (not like the sponge)enters and leaves (not like the sponge)
b.b. 2 cell layers :2 cell layers : ectodermectoderm – protects and covers outside– protects and covers outside
endodermendoderm – inner layer that lines the– inner layer that lines the
sac-like digestive cavitysac-like digestive cavity
***they have specialized cells***they have specialized cells
c.c. **organized tissues – muscle tissue and a nerve net**organized tissues – muscle tissue and a nerve net
Why? Refer to page 323Why? Refer to page 323
d.d. Central cavity with only 1 opening called theCentral cavity with only 1 opening called the gastrovascular cavitygastrovascular cavity
- this is the opening (mouth) where food enters and- this is the opening (mouth) where food enters and
leavesleaves
e.e. All have tentacles withAll have tentacles with nematocystsnematocysts
tentacles – arm like projections surrounding the mouthtentacles – arm like projections surrounding the mouth
nematocyst – stinging cells on the tentacles whichnematocyst – stinging cells on the tentacles which
shoot poisonous threads or dartsshoot poisonous threads or darts

5. Body FormsBody Forms
• Polyp diagram – page 324Polyp diagram – page 324
• See overhead diagramSee overhead diagram
• Medusa diagram – page 324Medusa diagram – page 324
• See overhead diagramSee overhead diagram

6. LOCOMOTIONLOCOMOTION
1.1. Stays in place – attached to rockStays in place – attached to rock
examples: sea anemone and coralexamples: sea anemone and coral
2.2. MedusaMedusa
example: jellyfishexample: jellyfish
move around – swim by pumping water in and out ofmove around – swim by pumping water in and out of
digestive cavitydigestive cavity
calledcalled jet propulsionjet propulsion – pumping water in and out of– pumping water in and out of
cavitycavity
3.3. PolypPolyp
example: hydraexample: hydra
crawlscrawls
See diagramSee diagram

7. FOOD GETTINGFOOD GETTING
*captures food with nematocysts by*captures food with nematocysts by
paralyzing small animals that swim intoparalyzing small animals that swim into
tentaclestentacles
• Nematocyst fire poison dartsNematocyst fire poison darts
• Paralyzes preyParalyzes prey
• Tentacles bring food to mouthTentacles bring food to mouth

8. REPRODUCTIONREPRODUCTION
1.1. Sexually – sperm and eggSexually – sperm and egg
**separate sexes**separate sexes
2.2. Asexually –Asexually –
Budding example: HydraBudding example: Hydra
RegenerationRegeneration