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Animal Bauplan
Animals
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Eukaryotic, multicellular and heterotrophic organisms
Tissues that develop from embryonic layers
Possess mitochondria
Enzymes to digest food inside the body
No cell walls
Proteins – Collagen only found in animals
Two cell types which are not found in any other organisms
o Muscle cells
o Nerve cells
Cells organised into tissues

Reproduction and development
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Sexual reproduction (except parthenogenesis)
Diploid stage dominates
Haploid stage – sperm and eggs produced by meiosis
Flagellated motile sperm and non-motile egg forming zygote
Body plan results from:
o Pattern of development driven by genome
o Millions of years of evolution
o Gastrulation
Symmetry – presence or absence
Tissues – some have tissue, formed from Gastrulation
Body Cavity (Coelom) – in triploblastic animals, a fluid or air filled cavity between the
digestive system and the outer body cover – protection of organs
Segmentation
Appendages
Skeleton

Evolution of Animals
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Choanoflagellate – aquatic protist
Adhesive cell bodies allow formation of colonies
Collar consisting of microvilli and flagellum move and form water current, bringing in
bacteria and other organisms and trapping them to be consumed
Collar cells found in many animals such as cnidarians, echinoderms and flat worms, almost
identical to Choanoflagellate – not found in protists, plants or fungi
DNA sequences show choanoflagellates and animals are sister groups

Parazoa: Phylum Porifera (Sponges)
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No symmetry
No tissues
No body cavity
300 freshwater species
7000 marine species
Body covered in tiny pores – canals – larger holes
Canals lined with specialised collar cells (Choanocytes)
Water is brought in and edible particles (e
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Bacteria) filtered out and consumed by cells

Reproduction
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Budding
Sexual
o Sponges are hermaphroditic but do not fertilise themselves
o Sperm and ova released into ocean

Eumetazoa
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Multicellular organisms with true tissues
Pass through distinct embryonic stages during development
Presence of symmetry – radial or bilateral
Tissues formed from Gastrulation
Presence or absence of a body cavity
Segmentation
Appendages
Skeleton

Radial Symmetry
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Body parts radiate from the centre
Any plane through the animal creates two equal halves
No left or right sides
Anemones, corals, etc
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Only as polyps
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Ctenophora (Comb Jellies)
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Diploblastic?
o Third membrane between ectoderm and ectoderm (Bilateria)
Molecular evidence not clear
Eight rows of comb like plates composed of fused cilia – sea walnut
Some have a pair of long retractable tentacles
Armed with adhesive structures (Colloblasts) which secrete sticky thread to capture food

Bilateral Symmetry – Bilateria
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Two sides – left and right – plane through the animal produces two equal halves
Controlled mobility
Cephalisation – development of a distinct head
Dorsal, ventral, anterior and posterior sides
Dorsal sides sometimes protected
Ventral sides usually have developed structures for locomotion
Triploblastic – three primary germ layers – ectoderm, endoderm, mesoderm
May or may not have a body cavity
Triblastic Gastrulation – three layers of tissue

Acoelomates – no body cavity
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Semi-solid mesodermal tissues between gut and body surface hold the organs in place
Flatworms

Pseudocoelomates
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Pseudocoelom – partially lined from mesoderm and endoderm
Acanthocephalus

Coelomates
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True body cavity (fluid filled)
Coelom – lined with mesoderm (Peritoneum)
Annelida

Body Cavity
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Locomotion
Circulation
Protection of organs
Reduced movement of body wall
Storage – fats

Protostomes versus Deuterostomes
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Key developmental processes
Major differences during embryonic development

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Cleavage
Gastrulation/ Neurulation
Patterning/ body plan formation
Tissue differentiation
Nature and complexity of these processes depends on the phylogenetic position of the
animal
Development driven by cell division, migration and differentiation

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Fertilization
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Water
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Land
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Sperm/egg interaction critical in ocean, e
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coral spawning
Synchronised spawning (temperature, moon, day length)
Sea Urchin – water velocity plays important role
Chemical chemoattraction (L-tryptophan in abalone)
Sperm needs to be protected from desiccation

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Spermatophore (tough casing) also used by aquatic animals (cephalopods,
decapods)
Transfer into female genital tract
Sperm in seminal fluid

Cleavage
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Rapid mitotic division immediately after fertilisation

Spiral Cleavage (Protostomes)
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Cleavage plane rotates on a spiral axis (between divisions)
Cells of the upper layer are located in the angles between the cells od the lower layer
Cleavage fate map – predetermined differentiation, e
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Arenicola marina
o If the cells are separated each has the ability to develop into an organism of it’s own

Nematode Cleavage
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Symmetric
Asymmetric
Symmetric and asymmetric

Radial Cleavage (Deuterostomes)
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Cleavage plane alters at 90° angles between divisions
Cells of the upper layer are located directly above the cells of the lower layer
Plastic – indeterminate differentiation
If the cells are separated from each other they will die; neither has the potential to develop
into an organism of its own

Gastrulation
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First series of cellular migrations in an embryo
Three germ layers are established
Physical construction of anterior / posterior axis
Neurulation and Organogenesis
Body plan formation
Tissue differentiation



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