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Animal diversity 2 - Animalswithout a coelomKey concepts• Simple animals may be

evolutionarily successful, havediverse life styles and behavior!

• Basic biology ofPorifera/ Cnidaria/Platyhelminthes/ Nematoda

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Mapping body plan characterson the tree

PORIFERA

CNIDARIAPLATYHELM

INTHESNEM

ATODA

PROTOSTOMESDEUTEROSTOMESARTHROPODA

ANNELIDA

MOLLUSCA

ECHINODERMATA

CHORDATA

PROTISTAMULTICELLULARITYEXTRACELLULAR DIGESTION

TISSUES

RADIAL SYMM

ETRY

BILATERAL SYMMETRY

MOUTH AND ANUS

MO

UTH AND ANUS TRUE COELOM

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Today: phyla without a true coelom

PORIFERA

CNIDARIAPLATYHELM

INTHESNEM

ATODA

PROTOSTOMESDEUTEROSTOMESARTHROPODA

ANNELIDA

MOLLUSCA

ECHINODERMATA

CHORDATA

PROTISTAMULTICELLULARITYEXTRACELLULAR DIGESTION

TISSUES

RADIAL SYMM

ETRY

BILATERAL SYMMETRY

MOUTH AND ANUS

MO

UTH AND ANUS TRUE COELOM

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Diversity of Sponges

A. Body plan -cells inextracellularmatrix, tubestructurewith flow ofwaterbringingfood to cells

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B. FeedingIf choanocytes specialized forfeeding, how are other cell typesnourished?

via another cell type- amoeboid cellsthat movethroughout thesponge, collectingand furtherdigesting materialfrom choanocytes,then passing it onto other cells...

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Diversity of SpongesC. ReproductionAsexual - branches may ‘pinch’ off and

regenerateSexual - most are hermaphroditesHermaphrodite - single individual produces

both male and female gametes

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Diversity of SpongesSperm are produced

from modifiedchoanocytes, releasedinto the environment

A ‘smoking sponge’releasing sperm

Choanocytes of othersponges ‘capturesperm’ in intracellularcapsules, thentransform intomigrating amoeboidcells, carry sperm to anegg! 7

Diversity of Sponges

The zygote (fertilizedegg) givesrise to swimminglarva -with choanocytes onoutside formovement

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Diversity of SpongesC. ReproductionLarva eventually settles, gives rise to

mature sponge

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Diversity of CnidariaTwo basic body formsThe polyp and the medusa - a

sedentary and mobile form

Polyp Medusa

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Many cnidarians have both forms in theirlife cycle, in others, one formpredominates

Which form predominates in jellyfish? Insea anenomes? In coral?

Polyp Medusa

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Diversity of CnidariaFeedingAdaptations for feeding and defense

- nematocysts - organelles thatfunction like miniature harpoons

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NematocystsTrigger senses ‘foreign’ chemical profile

a trigger

b ‘harpoon’

‘Harpoon’ released - can pierce a crab shellReleases toxin - some specieshave toxins fatal to humans

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Diversity of CnidariaWhat do cnidarians use their

nematocysts for?Capturing preyDefense against predatorsDefending territories (video

segment)

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Diversity of Cnidaria:Corals inparticular…Corals - polyp-form cnidarians, live in large

colonies, and secrete calcium carbonate

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Corals in particular…Corals - polyp-form cnidarians, live in

large colonies, and secrete calciumcarbonate

When old polyps die, new ones build ontop

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Diversity of CnidariaA coral reef is millions of coral

skeletons with living ones on theperiphery

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Coral polypswithzooxanthellae

Corals in particularWhere are the autotrophs in the coral reef

community? Corals live in shallow, clear,nutrient-poor water...

Corals get much of their energy fromphotosynthesizing plant-like protists -“zooxanthellae” that live within theircells

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Diversity of CnidariaZooxanthellae are dinoflagellates that have

developed a mutualism with coralsMutualism; interaction between species in

which both partners benefit

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Corals in particularEnvironmental threats

to the coral -zooxanthelleinteraction

Ocean pollution - lightcan’t penetratecloudy waters

“Coral bleaching-”corals lose theirzooxanthellae - arecent seriousproblem

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Coral bleaching: What causes it?Various factors, pollution, UV

irradiation, and most importantly,heat

Because of global warming, somepredictions that coral reefcommunities may be extinct within50 years

But there’s somehope the coralsare ahead of us insolving this problem

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Coral bleaching: The “adaptivebleaching hypothesis”

Bleaching can be adaptive ifcorals give upzooxanthellae adapted toold environment and pickup new ones, with forexample, increased heattolerance

Some evidence for this butstill controversial

And it’s a high risk strategy -corals have a limitedamount of time to reaquirezooxanthellae beforethey’re dead

Dead coral beingcolonized by algae 22

Diversity of Cnidaria

ReproductionAsexual reproduction - budding off

from polypsSexual reproduction - fertilized eggs

give rise to mobile, planktonicforms

Plankton - small ocean organismsthat drift with water movement

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Flatworms (Platyhelminthes) andRoundworms (Nematoda)

PORIFERA

CNIDARIAPLATYHELM

INTHESNEM

ATODA

PROTOSTOMESDEUTEROSTOMESARTHROPODA

ANNELIDA

MOLLUSCA

ECHINODERMATA

CHORDATA

PROTISTAMULTICELLULARITYEXTRACELLULAR DIGESTION

TISSUES

RADIAL SYMM

ETRY

BILATERAL SYMMETRY

MOUTH AND ANUS

MO

UTH AND ANUS TRUE COELOM

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PlatyhelminthesBody planNo body cavityIn most mouth but no anusLack circulatory, respiratory

system, absorb O2 throughbody wall

Movement?slowly, through muscle

contraction and/or beat cilia in slime trail!

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PlatyhelminthesFeedingSome free-living, many parasitesi. Some of the parasites with complex life

cycles: several different forms and morethan one host

Human liver flukemust passthrough two otherhosts to completelife cycle

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PlatyhelminthesExample of a human platyhelminthes

parasite: Schistosoma

1) Parasiteeggs shedin humanwaste,gets intowater

2) Eggs hatch, infect snails

3) Snails shedswimming stage

4) Burrowinto humanskin, infectorgans,reproduce 27

The platyhelminth parasiteSchistosomaHumans (where parasite reproduces)

thedefinitive hostSnails the intermediate host 1) Parasite

eggs shedin humanwaste,gets intowater

2) Eggs hatch, infect snails

3) Snails shedswimming stage

4) Burrowinto humanskin, infectorgans,reproduce 28

The platyhelminth parasite,Schistosoma

- causes schistosomiasis- found throughout tropical Asia, sub-

Saharan Africa, mid-East and LatinAmerica

- 200 million people infected, chronicinfection damages the liver, intestines,lungs, 20 million develop ‘severeconsequences’

- What changes could help reducedisease transmission?

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Platyhelminthes

Reproduction- some asexual - e.g. can cut

Planaria in two

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- sexual, most hermaphrodites - two hermaphrodites lie next to each other, each donates sperm to the other’s egg sac

Body planFeeding

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Nematoda - roundwormsBody plan- very simple - “a tube within a tube”

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Nematoda - roundwormsBody planHave a pseudocoelom for body

cavity

Have a one-way digestive system: amouth and an anus

Mesoderm linesthe body wall butdoesn’t surroundthe gut

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Nematoda - roundworms20K species, range in length

from 0.3 mm to 8 m (in whaleplacenta *)

* What was it doing there?

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Nematoda - roundworms

FeedingMany free living decomposers

andparasites of almost everything -

plants and animals

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Nematoda - roundwormsFeedingMany free living decomposers

andparasites of everything - plants

and animals

Example - Trichinella35

On cooking pork...Trichinella, a roundworm parasite of

mammals, including rodents, pigs andhumans

Pigs get infected from eating uncookedmeat scraps or from rodentcontamination, humans from eatingundercooked pork

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On cooking pork...

• Short-term symptoms - abominal pain,vomiting, fatigue and fever

• Then, headaches, fever, aching jointsand muscles

• Later most symptoms subside - chronicinfection

•Trichinella worms lay eggs in intestine,young larvae travel through arteries andencyst in muscles - can live for years

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On cooking pork...Trichinosis not very common any moreIn 1940, 16% of US human population

infectedIn 1970, 4%In 1991-1996, average of 38 cases per yearWhy the improvement?No raw meat fed to hogs, rodent control,

stringent inspections, and freezing andthorough cooking of pork more common

Still a concern with wild game, esp. bearmeat

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What about Wilbur?

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Nematoda - roundwormsWhen parasites are our allies- the use of insect-parasitic

nematodes for control of pests

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Nematoda - roundwormsNematode parasites sometimes have

mutualistic bacterial associatesInsect-parasitic nematodes release

bacteria in the host, the bacteria killthe host

Some of thesebacteria areluminescent!

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Nematodes that cause riverblindness, elephantiasis in humansalso have mutualist bacteria

Just recently led to new therapies with antibiotics

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Nematoda - roundwormsReproductionSexual - some species have

both sexes, some arehermaphrodites

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Nematoda - roundworms

ReproductionThe record for reproductive output?Ascaris the parasitic roundworm,

produces 100,000 - 200,000 eggsper day!

Assuming population isn’t growing,what does this say about mortalityof immature stages?

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