The three grades of metazoan animals

MesozoaParazoa

PoriferaPlacozoa

Eumetazoa

All other animal phyla

GRADE:

PHYLA: Mesozoa

KINGDOM: Animalia

General Body Plan

• Cellular level of organization

• Asymmetrical

• Choanocytes

• Mesohyl

spongin/ collagen

spicules

3 Body Types

• Asconoid

• Syconoid

• Leuconoid

Increasing size Increasing Surface Area :Volume

Based on the complexity of the water canals:

The three grades of metazoan animals

MesozoaParazoa

PoriferaPlacozoa

Eumetazoa

All other animal phyla

GRADE:

PHYLA: Mesozoa

KINGDOM: Animalia

Phylum Cnidaria

                                          

Level of Organization

Tissue

-similar cells are organized into tissues that work together to accomplish a common function

-Cnidarians are diploblastic: they have 2 germ layers

Tissue Layers

Diploblastic = 2 germ layers

• endoderm gastrodermis (inner tissue)• ectoderm epidermis (outer tissue)

mesoglea• gelatinous/ noncellular matrix between the 2 layers

Tissue Layers

epidermis

mesoglea

gastrodermis

gastrovascular cavity (GVC)

Epidermal Cell types

Epitheliomuscular cell

neurons

receptors

• cnidocytes: epidermal cells containing stinging organelles (nematocysts). Unique to Cnidarians.

cnidocyte

Epidermal Cell types

Epidermal Cell types

Undischarged

Cnidocil: trigger

cnidocyte

Epidermal Cell types

neamtocyst

discharged

cnidocyte

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

Jellyfish sting

Gastrodermal Cell types

gastrodermisepidermis

mesoglea

nutritive-muscular cells (ciliated)

gland cells

General Body Plan• sac-like body (only 1 opening)

Gastrovascular cavity

oral surface

aboral surface

mouth

epidermis

gastrodermis

mesoglea

Dimorphism: 2 different body forms are usually present in the life cycle:

General Body Plan

oral

aboral

aboral

oral

- Radially symmetrical: body parts are arranged concentrically around an oral-aboral axis

oral

aboral

General Body Plan

General Life Cycle

Asexual reproduction

Sexual reproduction

Feeding and Digestion

Feeding– nematocysts capture prey– tentacles

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

Feeding and Digestion•Food and waste go in/out the same opening

no anus!

Food

waste

gastrodermis

epidermis

mesoglea

nutritive-muscular cells: create water currents, circulate food particles in GVC

gland cells: secrete mucus, entraps food particles

Feeding and Digestion

Nervous System

– nerve net

(no central nervous system= no brain)

receptors

neuronsnerve net

Nervous System

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

Nervous System

ocelli

statocysts

Skeletal Support

– water in GVC acts as a hydrostatic skeleton

Muscles act against water trapped in the GVC

Skeletal Support•water within GVC acts as a hydrostatic skeleton:

Skeletal Support

Reproduction

Asexual– pedal laceration

(e.g. sea anemones)

Reproduction

Asexual– budding

Buds

Reproduction

Asexual– longitudinal fission

Reproduction

Sexual– usually dioecious

(separate sexes)– monoecious

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

Phylum Cnidaria

Three Classes:

Class Hydrozoa

Class Scyphozoa

Class Anthozoa

These classes differ in the prominence of the polyp and medusa stages

Class Hydrozoa

• medusa & polyp body forms

Fire coral

Class Hydrozoa

• medusa & polyp body forms

• most are colonial colonies are formed of individuals (zooids)

a single zooid

Class Hydrozoa

• many of these colonies are polymorphic

there are several different types of polyps/zooid and

each type is specialized for a different function

all the zooids within a colony are genetically identical

and are connected by a common GVC

Class Hydrozoa

                                       

gastrozooid

gonozooid

- a sessile colony showing polymorphism

entire colony

GVC

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

scyphistoma

strobila

ephyra

adult medusa sperm and egg

larva

Class Anthozoa

• polyp body form ONLY • all marine

Class Anthozoa

• some are colonial colonies are formed of individual zooids (e.g. corals)

• some are solitary (e.g. anemones)

Class Anthozoa

Sea anemones

Class Anthozoa

                                                 

Soft Corals

Sea pen

Sea pansy

Class Anthozoa

                                                 

                            

Stony Corals

Class Anthozoa- life cycle

eggsperm

larva

Sexual reproduction

Class Anthozoa- life cycle

asexual reproduction

fission

pedal laceration

fission

Colony formation

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

common GVCindividual polyp

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

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

Distribution of Coral Reefs

Coral Species Diversity

Number of coral species increases with decreasing depth:

• increasing illumination

•Increasing radiant energy

Distribution of Coral Reefs

Habitat requirements

1. High light

2. Clear water

3. Water temp: 20 0 – 28 0 C

Required for zooxanthellae

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)

Coral bleaching

FSU Research on Cnidarians: Dr. Don Levitan

Levitan@bio.fsu.edu Reproductive isolation in broadcast-spawning marine invertebrates.

Biological species concept: a species is a population or group of populations that can potentially interbreed and produce viable,fertile offspring, but that is reproductively isolated from other populations.

Western meadowlark Eastern meadowlark

How do species of broadcast-spawning marine invertebrates remain reproductively isolated from one another?

The Montastrea annularis species complex

1. Montastrea annularis

2. Montastrea faveolata

3. Montastrea franksi

M. annularis M. faveolata

M. franksi

Gamete bundles: contain sperm and

eggs

Gamete bundles are released and float to the surface. At the surface, sperm an eggs are released.

The Montastrea annularis species complex

1. Montastrea annularis

2. Montastrea faveolata

3. Montastrea franksi

All three species are sympatric, and spawn ~ 8 days after a full moon in late summer

Lee Stocking Island

San Blas

Bocas del Toro

Curacao

How do species of broadcast-spawning marine invertebrates remain reproductively isolated from one another?

1. Time of spawning

Do species spawn at the same time after sunset?

Do species spawn at the same time after sunset?

M. franksi spawns earlier than both M. faveolata and M. annularis

Levitan et al. 2004

2. Gametic compatibility experiments

Are gametes from different species compatible?

egg

sper

m

M. an M. fr M. fav

M. an

M. fav

M. fr

Measure fertilization

success

Bahamas

0

20

40

60

80

100

a v k

aa vv kk

as k

e

ks a

e

vs a

e

as v

e

ks v

e

vs k

e

Cross type

Per

cent

Fer

tiliz

atio

n

A AAB

B

C C C C CC C C21 6 17

104

8

70

93

89 34 33 32 33

M. faveolata x M. annularis

M. faveolata x M. franksi

M. franksi x M. annularis

Levitan et al. 2004

How do species of broadcast-spawning marine invertebrates remain reproductively isolated from one another?

The Montastrea annularis species complex

1. Montastrea annularis

2. Montastrea faveolata

3. Montastrea franksi

Gametes incompatible

Spawn simultaneously

Spawns earlier than the other 2

Gametic compatibility with M. annularis, incompatible with M. faveolata

How do species of broadcast-spawning marine invertebrates remain reproductively isolated from one another?

•In the M. annularis species complex, reproductive isolation is due to a combination of:

1. Temporal isolation

2. Gametic isolation

3. Spatial isolation- depth

•None of these mechanisms is completely effective on its own, but together they result in isolation