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

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 HYDROZOA SCYPHOZOA

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

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 stomatodeum 4. Micromeres divide and spread over aboral pole and macromeres

Cleavage in PleurobranchiaCleavage in Beroe

CTENOPHORA LARVAE

COMPARISON OF CNIDARIA AND CTENOPHORE CNIDARIACTENOPHORA Diploblastic with acellular mesoglea Diploblastic (triploblastic?) with cellular mesenchyme Radial symmetryBiradial symmetry ; oral/aboral axes NematocystsColloblasts Gastrovascular body cavity Nerve netMore specialized nerve net Musculature – extensions of epithelial cellsMusculature – from mesenchyme cells Alternation of generationsNo alternation of generations Planula larvaCydippid 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 EctodermMesodermEndoderm

TURBELLARIA – MAJOR ORGAN SYSTEMS