13. radiate animals

7/27/2019 13. Radiate Animals

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Radiate Animals

Chapter 13


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Radiate Animals

Phylum Cnidaria & Phylum Ctenophora

Radial Symmetry

Diploblastic 2 embryonic tissue layers


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Phylum Cnidaria

All animals except

sponges belong to

the clade

Eumetazoa, theanimals with true

tissues.


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Phylum Cnidaria

Phylum Cnidaria is

one of the oldest

groups in this clade.

Fossil history back700 MY.


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Phylum Cnidaria

Cnidarians have:

Radial symmetry

Gastrovascular cavity extracellular

digestion

Tissues derived from two embryonic

germ layers

Cnidocytes special cells with stingingorganelles called nematocysts.


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Phylum Cnidaria

Cnidarians have

diversified into a wide

range of both sessile

and floating formsincluding jellies,

corals, and hydras.

Polymorphism

some species existas both polyps and

medusae during their

life cycles.


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Phylum Cnidaria

The basic body plan of a cnidarian is a

sac with a central digestive

compartment, the gastrovascular

cavity.

A single opening functions as both mouth

and anus.


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Phylum Cnidaria

In colonial forms that

share a

gastrovascular

cavity, polyps maybe specialized for

feeding,

reproduction, or

defense.


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Body Wall

Cnidarians have an

outer tissue layer,

the epidermis,

derived fromectoderm, and an

innergastrodermis,

derived from

endoderm, withjellylike mesoglea in

between.


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Body Wall

The epidermal layer contains several types of

cells organized into tissues.


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Reproduction

Polyps can reproduce asexually by

budding, fission, or pedal laceration.


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Reproduction

Cnidarians, typically medusae, can also reproduce

sexually.

A zygote usually develops into a motile planula larva.

Some species only exist as polyps, others only asmedusae, others alternate between the two.


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Feeding

Cnidarians are carnivores that use tentacles tocapture prey.

The tentacles are armed with cnidocytes uniquecells that function in defense and the capture of prey.

Nematocysts contain toxins used for prey capture anddefense.


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Feeding

Nematocysts are

used to inject a

toxin.

Variable in form.

May be used for

prey capture or

defense.


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Feeding

Extracellular digestion begins in the

gastrovascular cavity, but is completed

within the cells of the gastrodermis.

Some cnidarians supplement their diet

with nutrients collected from algal

symbionts (zooxanthellae).


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Nerve Net

Cnidarians have a diffuse nervous

system.

Nerve cells forming two interconnected

nerve nets in the epidermis andgastrodermis.

No concentrated grouping of nerve cells

forming a central nervous system. No advantage for radially symmetrical animals

where stimuli approach from all sides.


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Classification

The phylum Cnidaria is divided into four

major classes:Class Hydrozoa Class Scyphozoa Class Cubozoa ClassAnthozoa


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Classification

A fifth class, Staurozoa, has been

proposed.

No medusae in life cycle but polyp topped

by medusa-like region.


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Phylum Cnidaria

Class Staurozoa Commonly called stauromedusans

No medusa stage.

Solitary polyp body that is

stalked. Uses adhesive disk to attach to

seaweeds, and objects on seabottom.

Polyp top resembles a medusa

with eight extensions (arms)ending in tentacle clusterssurrounding mouth.

Reproduce sexually.


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Class Hydrozoa

Hydrozoans are

variable in form.

Mostly marine.

Usually colonial,sometimes solitary.


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Class Hydrozoa Typical Life Cycle

Most hydrozoans alternate between polyp

and medusa forms.

Some have only polyps.

Some have only medusae.


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Class Hydrozoa - Polyps

Typical hydroids have abase, a stalk, and one ormore terminal zooids(individual polyp animals).

Thecate presence of aprotective cup aroundthe polyp. Obelia

Athecate no suchprotection. Ectopleura


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Class Hydrozoa - Medusae

Hydroid medusae are usually

smaller than those in the

class Scyphozoa.

Gastrovascular cavity is

continuous from mouth totentacles and is lined by

gastrodermis.

Velum, inward projection of

the bell, is present. Specialized organs:

Statocysts equilibrium

Ocelli light sensitive


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Class Hydrozoa

Members of the order

Siphonophora, such as

the Portuguese man-of-

war, are actually colonies

of polyp individuals.

One polyp may be gas

filled and used as a

float.

Feeding polyps each

with one long tentacle

Reproductive polyps


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Class Hydrozoa

Hydrocorals

resemble true corals.

Calcareous

skeleton Fire coral


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Class Scyphozoa

In the class

Scyphozoa, jellies

(medusae) are the

prevalent form of thelife cycle.

No velum present.

Rhopalium sense

organ containingstatocysts and

sometimes ocelli.


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Class Scyphozoa

Tentacles around

the periphery of the

bell contain

nematocysts used toparalyze prey

animals.

In the center are four

frilly oral arms usedto capture and ingest

prey.

C S f


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Class Scyphozoa Typical Life

Cycle

Planula larvae

develop into a

polyp-like form.

Saucer-likebuds called

ephyrae are

produced by

strobilation.


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Class Cubozoa

In the classCubozoa, whichincludes box jelliesand sea wasps, the

medusa is box-shaped and hascomplex eyes.

Polyps are tiny anddevelop directly intomedusae.


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Class Cubozoa


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Class Anthozoa

Class Anthozoaincludes thecorals and seaanemones which

occur only aspolyps nomedusa stage.

All marine

Solitary orcolonial


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Sea Anemones Order Actinaria

Found in coastal

waters all around the

world.

Attach to rocks usingtheirpedal disc.

Feed on fish or any

other food of suitable

size.


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Sea anemones usually move by gliding slowly

along on their pedal discs.

When a predator approaches, most withdraw.

Stomphiadetaches its disc and swims away.


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Tentacles arranged around the central mouth.

The gastrovascular cavity is divided into sixradial chambers.

Increases the surface area of the gastrodermis.


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Mutualisms

Sea anemones sometimes harbor

zooxanthellae (photosynthetic protists)

like hard corals do.

Some crabs will decorate their shells

with anemones.


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Mutualisms

Some damselfish (anemone fishes) form

associations with large anemones.

Fish gains protection from living in the

anemone. The fish may help ventilate the anemone, or

keep it free of sediment.


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Hexacorallian Corals

Hexacorallian

corals (Order

Scleractinia)

are the true orstony corals.

Like tiny

anemones living

in calcareouscups.


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Hexacorallians(SubclassHexacorallia) havea gastrovascular

cavity subdivided bysepta in multiples ofsix.

The calcium

carbonate skeletonis secreted belowliving tissue.


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Polyps may be retracted into the skeleton.

Often retracted during the day.

The polyps expand for feeding.


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Tube Anemones and Thorny Corals

Members of

subclass

Ceriantipatharia.

Have coupled butunpaired septa.

Tube anemones

Solitary and live in

soft sediments.


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Tube Anemones and Thorny Corals

Thorny or black corals

Colonial and attach to firm substrata.

Both groups have few species and live in

warmer seas.


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Octocorallian Corals

Members of theSubclass Octocorallia

have eight pinnate

tentacles and eight

septa.


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Octocorallian Corals

Sea fans, sea pens & sea pansies belong to

this group.

Often beautifully colored.


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Cnidaria

MedusozoaAnthozoa Staurozoa Scyphozoa Cubozoa Hydrozoa

Trachyline-

like

hydrozoaGut with

septalfilament

sSiphonoglyph

Anthozo

an

pharynx

Hexaradial

and

octaradialsymmetry

Creeping

planula

without cilia

Strobilation Complex eyes

Velarium

Boxlike

medusa body Polyp lost

Velum in medusae

Medusae produced by

lateral

budding and entocodonMedusoid body form

Motor nerve net

Primary polyp tentacles hollow

Mouth surrounded by solid tentaclesPlanula larva

CnidocytesRadial, polypoid body form

RhopaliumPolyp

reduced

or lost

Hydroids Man-of-war Other

hydrozoa

Phylum Cnidaria


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Coral Reefs

Coral reefs are one of the most productive

and diverse ecosystems on Earth.

Found in shallow tropical seas.

They require warm water. Sunlight required for symbiotic zooxanthellae.


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Coral Reefs

The main structure of

the reef is calcium

carbonate secreted by

hermatypic (reef-

building) corals and

coralline algae.


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Coral Reefs

Octocorallian corals and some

hydrozoans (those known as fire coral)

also contribute calcium carbonate.


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Types of Reefs

Fringing reefs are close to a landmass with

no lagoon or a narrow lagoon.


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Types of Reefs

Barrier reefs run parallel to shore and have a

wide, deep lagoon.


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Types of Reefs

Atolls are reefs that encircle a lagoon, but

not an island.


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Types of Reefs

Patch reefs are scattered throughout a

lagoon.


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Reef Zones

The fore reef slope, orreef front, is the side thatfaces the sea. Slopes into deeper water.

The reef crest is the shallow or even slightly emergenttop of the reef.

The reef flat is the shallow back reef area that slopesinto the lagoon.


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Coral Reefs

Nutrients from fertilizerand sewage threatencoral reefs withexcessive algal growth.

Coral reefs in manyareas are threatenedby factors mostly ofhuman origin.

Higher atmospheric concentrations of carbondioxide (from burning hydrocarbon fuels) tendsto acidify ocean water, which makesprecipitation of CaCO3 by corals more difficultmetabolically.

http://www.youtube.com/watch?v=QAaRJKKTOys
http://www.youtube.com/watch?v=QAaRJKKTOyshttp://www.youtube.com/watch?v=QAaRJKKTOys


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Coral Reefs

Symbiosis betweenzooxanthellae and coralsis threatened by globalwarming. Warmer water damages the

photosynthetic mechanismin zooxanthellae.

Coral tissues turn white and

brittle, this is called coralbleaching.

Zooxanthellae die or areexpelled by corals.


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Phylum Ctenophora

Phylum

Ctenophora are

the comb jellies.

No nematocysts. Tissue level of

organization, like

cnidarians.

Mostly freeswimming.


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Phylum Ctenophora

They use theirciliated combplates forswimming.

Not strongswimmers.

Ctenophores arebioluminescent.

Statocystsense organ


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Phylogeny

Cnidarians may have evolved from a radiallysymmetrical planula-like ancestor.

Trichocysts and toxicysts found in some

ciliates may be precursors to nematocysts.

13. radiate animals

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