BASAL METAZOANS

Bauplan (pl. Baupläne) The generalized body plan of an archetypal member of a major taxon.

A body plan, baupläne, ground plan, ground pattern, or bodyplan, is "an assemblage of morphological features shared among many members of a phylum-level group"

Look at 4 groups

1. Placozoa

2. Cnidaria

3. Ctenophora

4. Platyhelminthes

PLACOZOA

PLACOZOA

Distribution

PLACOZOA

1) Asymmetric.

2) No distinct tissues or organs.

3) No nervous system.

4) No body cavity or digestive cavity.

5) Body is shaped like a flat disc.

6) Two layers of single cells.

7) Marine.

8) One species only known Trichoplax adhaerens

Characteristics of Placozoa

PLACOZOA

Cover cells

Cylinder cells

Gland cells

Fibre cells

PLACOZOA

Placozoan movement

Feeding -

PLACOZOA

Reproduction

1. Binary fission

2. Budding

3. Sexual

PLACOZOA

Reproduction

1. Binary fission

2. Budding

3. Sexual

“hollow swarmer”

PLACOZOA

Reproduction

1. Binary fission

2. Budding

3. Sexual

“hollow swarmer”

PLACOZOA

Reproduction

1. Binary fission

2. Budding

3. Sexual

PLACOZOA

Reproduction

1. Binary fission

2. Budding

3. Sexual

oocyte

yolk

zygote

Fertilization membrane

CNIDARIA

ANTHOZOA

CUBOZOA

HYDROZOASCYPHOZOA

Diploblasty

Gastroderm

Ectoderm

Mesoglea

CNIDARIA

Feeding

CNIDARIA - EMBRYOLOGY

Stereogastrula

Radial and holoblastic cleavage

CNIDARIA – PLANULA LARVA

Ectoderm

Endoderm

CTENOPHORA – COMB JELLIES

CTENOPHORA – BIRADIAL SYMMETRY

Tentacle

Statocyst

Tentacle sheath

Meridional canal

Stomadeum

Pharynx

Mouth

Anal pore

CTENOPHORA

Muscle fibres

CTENOPHORA TENTACLE

Ctenophora video

CTENOPHORA – SUPPORT & LOCOMOTION

Locomotion

- Comb rows

CTENOPHORA FEEDING - COLLOBLASTS

CTENOPHORE - STATOLITHS

- Balancing organ

Statocyst

CTENOPHORA – REPRODUCTION AND DEVELOPMENT

CTENOPHORA – REPRODUCTION AND DEVELOPMENT

1. Form blastomeres – meridional cleavage

2. Third division – 8 macromeres

3. Fourth division – latitudinal and unequal - micromeres

5. Macromeres invaginate (gastrulation)-micromeres become ectoderm-macromeres become endoderm

6. Just before gastrulation –- Produce additional micromeres on oral side – invaginate to form stomatodeum4. Micromeres divide and spread over

aboral pole and macromeres

Cleavage in PleurobranchiaCleavage in Beroe

CTENOPHORA LARVAE

COMPARISON OF CNIDARIA AND CTENOPHORE

CNIDARIA CTENOPHORA

Diploblastic with acellular mesoglea Diploblastic (triploblastic?) with cellular mesenchyme

Radial symmetry Biradial symmetry ; oral/aboral axes

Nematocysts Colloblasts

Gastrovascular body cavity Gastrovascular body cavity

Nerve net More specialized nerve net

Musculature – extensions of epithelial cells Musculature – from mesenchyme cells

Alternation of generations No alternation of generations

Planula larva Cydippid larva

PLATYHELMINTHES

Who are they?

Turbellaria(flatworms)

Trematoda (flukes)

Monogenea (flukes)

Cestoda (tapeworms

PLATYHELMINTHES

Common trends

1. Triploblastic acoelomates

2. Cephalization and central nervous system

3. Mesoderm – fibrous and muscular mesenchyme

4. Osmoregulatory structure - protonephridia

5. Elaborate reproductive systems

PLATYHELMINTHES

Limiting factors

l. Lack of efficient circulatory system

2. Lack of gas exchange system

TRIPLOBLASTY

Ectoderm Mesoderm Endoderm

TURBELLARIA – MAJOR ORGAN SYSTEMS