Tree of Life

The tree of life according to Ernst Haeckel, 1891

How does Porifera fit in?

Porifera

Other animals

unknown common ancestor

eukaryotemulticellular

heterotrophicBlastula stage

cellular level of organization

choanocytes

3 body types

How does Cnidaria fit in?

PoriferaOther animals

unknown common ancestor

eukaryotemulticellular

heterotrophicBlastula stage

cellular level of organization

choanocytes

3 body types

Cnidaria

Phylum Cnidaria

                                          

Level of Organization

Tissue

• cells are organized into tissues and work together to accomplish physiological functions

Tissue LayersDiploblastic = 2 germ layers

• endoderm gastrodermis• ectoderm epidermis

mesoglea• gelatinous matrix between the 2 layers

epidermis

mesoglea

gastrodermis

gastrovascular cavity

General Body Plan• sac-like body (only 1 opening)• Food and waste go in/out the same opening

no anus!• water within GVC acts as a hydrostatic skeleton

Gastrovascular cavity

mouthoral surface

aboral surface

epidermis

gastrodermis

mesoglea

General Body Forms2 different body forms are usually present in the life cycle:

polyp & medusa

** one animal may pass through both forms during its life **

General Life Cycle

Radial Symmetry- body parts are arranged concentrically around an oral-aboral axis

oral

aboral

Nematocysts

• specialized stinging organelles • found within cnidocytes (cells)• cnidocytes are located in epidermis

A cnidocyte with a nematocyst within it

Nematocysts• nematocysts are like “mini-harpoons”• cnidocil senses movement & acts like a “trigger”• can inject poison, coil around prey, or be adhesive • functions:

- prey capture; defense

Undischarged Discharged

cnidocil

cnidocyte

nematocyst

Colony formation

• colony formation is common (colonial animals)• occurs via asexual reproduction (e.g. fission)• individual polyps are connected to one another by

the GVCindividual polyp

Physiology

Feeding– nematocysts within cnidocytes– tentacles

Digestion– extracellular (in GVC)– intracellular (by gastrodermal cells)– incomplete system (no anus)

Gas exchange & Excretion – these systems are absent

Physiology

Nervous System– nerve net

(no central nervous system= no brain)– sense organs

– statocysts (equilibrium organs)– ocelli (photosensitive organs)

Skeletal System– water in GVC acts as a hydrostatic skeleton

Physiology

Reproduction

Asexual– budding– longitudinal fission– pedal laceration

(e.g. sea anemones)

Physiology

Reproduction

Sexual– usually dioecious

(separate sexes e.g. humans)– monoecious

(both male + female gonads in 1 individual)– results in Planula larva

Phylum Cnidaria

Class Hydrozoa

Class Scyphozoa

Class Anthozoa

Class Hydrozoa• medusa & polyp body forms

Fire coral

Class Hydrozoa• medusa & polyp body forms

• most are colonial colonies are formed of individual zooids

a single zooid

Class Hydrozoa

• many of these colonies show polymorphism

this is where there are several different types of

polyps/zooid and each type is specialized for a

different function

e.g. gastrozooids = feeding polyps

e.g. dactylzooids = defense polyps

all the zooids within a colony are genetically

identical

these different zooids work together in the colony

Class Hydrozoa

                                       

gastrozooid

gonozooid

- a sessile colony showing polymorphism

entire colony

Class Hydrozoa

gastrozooid

dactylzooid

- a Portugese Man-o-war is a floating hydrozoan colony showing polymorphism

entire colony

pneumatophore

Class Hydrozoa- life cyclesexual

reproduction

asexual reproduction

Class Hydrozoa

asexual reproduction

• Hydra is an example of a solitary, freshwater hydrozoan

sexual reproduction

gonads

bud

Class Scyphozoa

• “true” jellyfish• medusa & polyp body forms• thick mesoglea

Class Scyphozoa- life cycle

eggsperm

larvascyphistomastrobila

ephyra Adult medusa

Class Anthozoa• polyp body form ONLY • all marine

Class Anthozoa• some are colonial

colonies are formed of individual zooids

• some are solitary

Class AnthozoaSea anemones

Class Anthozoa

                                                 

Soft Corals

Sea pen

Sea pansy

Class Anthozoa

                                                 

                            

                                                                                               

       

Stony Corals

Class Anthozoa- life cycle

eggsperm

larva

Sexual reproduction

Class Anthozoa- life cycleasexual reproduction

fission

pedal laceration

fission

How does Cnidaria fit in?

Porifera

unknown common ancestor

eukaryotemulticellular

heterotrophicBlastula stage

cellular level of organization

choanocytes

3 body types

Cnidaria

tissue level of organization

diploblastic

3 classes:Hydrozoa, Scyphozoa, Anthozoa

2 body types: polyp, medusa

Symbiosis

Mutualism –• Corals contain endosymbiotic algae called

zooxanthellae • the zooxanthellae photosynthesize and provide

food for the coral while the coral provides a safe home

zooxanthellae

Symbiosis

Mutualism –• Many species of anemone fish (clown fish) live

within anemones and are immune to their stinging nematocysts

• the fish may lure in other fish for the anemone to capture and eat, while the anemone provides protection and a home

Coral Reefs

What are they?• stony corals lay down a calcium carbonate

skeleton• these skeletons are laid down on top of one

another and over thousands of years, form large calcium carbonate structures

• these large structures, along with the plants and animals that inhabit them, are known as

coral reefs

Where do they form? • in optimal conditions for their zooxanthellae

shallow, warm, nutrient-poor waters

Importance of Coral Reefs

• one of the most productive ecosystems

although the water is nutrient-poor• “hot spots” for biodiversity

Threats to Coral Reefs

• over-enrichment of nutrients from sewage and

agricultural run-off• overfishing of herbivorous fish• global warming (leads to coral bleaching where

corals expel their zooxanthellae)