Romina Angelelli
What is an animal?
 Multicelled heterotrophs that move
about while some are sessile but only
for part of their life.
 Body cells do not have a wall
 Typically diploid
 Most are invertebrates meaning no
backbone
Animal Body Plans
 Organization:
 Different cells carry out different tasks within the animal
 Cells are organized as tissues
 Tissue formation begins in an embryo
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At first embryos had two tissue layers the outer ectoderm and
the inner endoderm. (jellyfish and flatworms still do)
Now a new layer called the mesoderm has evolved. It lays
between both of the original layers and allows for increased
complexity of the organism as well as organs.
Animal Body Plans continued.
 Body Symmetry:
 Assymetrical (ex. Sponges)
 Radial Symmetry (ex. Jellyfish)
 Bilateral Symmetry (ex. Lobster)
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Most Bilateral animals have gone through cephalization.
Meaning nerve cells have been concentrated at the head end.
In some cases (lineages), evolved into a brain.
Animal Body Plans continued.
 Gut and Body Cavity:
 Most animals have a gut.
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Saclike gut= incomplete digestive system, food enters and waste leaves
through same opening.
Tubular gut= complete digestive system, mouth at one and and an anus
at the other. Perform several tasks simultaneously. Like taking in food,
absorbing nutrients, etc.
In most animals a fluid filled body cavity surrounds the gut. If
surrounded by mesoderm it is the coelom. If incompletely lined it is the
pseudocoel (false coelom).
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Advantages of Pseudocoel or coelom
 Materials can diffuse through fluid to body cells.
 Muscles can redistribute fluid to alter body shape and locomotion.
 Organs can grow larger and more freely.
 Differences in digestive system of two major lineages of bilateral
animals
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Protostomes: first opening that develops in embryo is mouth
Deutrostomes: first opening to develop in embryo is anus
Animal Body Plans continued.
 Circulation:
 In small animals, gases and nutrients can diffuse through a
body but in larger animals more is necessary to maintain
them alive, a circulatory system.
 Circulatory system:
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Closed- A heart or hearts propel blood through a continuous system
of vessels. Materials diffuse out into cells.
Open- blood leaves vessels and exchanges materials directly with
tissues before returning to the heart.
Closed system= faster blood flow
 Segmentation:
 Many bilateral animals are segmented
 When many segments specialize on the same tasks they cn
change and take on new functions.
Animal Origins
Adaptive Radiation
 It is said that animals
most likely evolved
from a colonial protist
similar to
choanoflagelletes.
 Fossils of early animals that lived
 Studies have shown
that these protists have
proteins similar to
those in animals.
in the seas 570 million years ago
were found in Australia’s
Ediacaran hills and therefore
called Ediacarans.
 Most don’t have any living
descendants.
 Several million years later
animals underwent a dramatic
adaptive radiation and by the
end of the period all major
animal lineages were present in
the seas. Speciation occurred
and all type of mutations were
occurring as well.
Relationships and classification
 Animals have traditionally been classified based on
morphology and developmental patterns.
 The traditional classification method puts a lot of
emphasis on possession of a body cavity.
 Recently gene sequence comparisons have been used
to investigate relationships.
 Relationships amongst animals are still being
investigated.
 Ex: recent genetic studies suggest that all invertebrates
that molt are closely related.
Simplest Living Animal
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Placozoan
Only one
Trichoplax adhaerens
No body symmetry
No tissues
4 different type of cells
Marine animal
2mm in diameter
Sticky, hairy plate
Smallest genome of any known animal
Close relative of choanoflagellates
Sponges
 Phylum Porifera
 Aquatic
 No symmetry, tissue, or
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organs
Differ in shape and size
Non flagellated cells on the
outside and flagellated collar
cells within
Jellylike matrix between the
cell layers
Intracellular digestion
Filter feeders
Serve as habitat
hermaphrodite
Phagocytosis
Cnidaria
 Cnidarians have nematocysts in their tentacles
 Nematocysts- stinging cells
 Nematocysts help capture prey and also function as a
defense
 Create a nerve net when interconnecting nerve cells
extend through the tissues
 Four classes: hydrozoans, anthozoans, cubozoans, and
scyphozoans.
 Two tissues with a jellylike layer that functions as a
hydrostatic skeleton between them.
Flatworms
 Platyhelminthes phylum
 Planarians
 Bilateral protostomes
 the simplest animals to have organ systems.
 Nerve cords connect to ganglia in the head and serve as
control center
 Saclike gut
 Pharynx to take in food and expel waste
 Tapeworms are parasitic flatworms. Their bodies are made
of units called proglottids. Flukes are also parasites.
Annelids
 Segmented worms (earthworms and polychaetes) and
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leeches
Circulatory digestive
Solute-regulating
Nervous systems extend through all coelomic chambers
Nephridia- regulate the composition of body fluid
Mollusks
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Sheetlike mantle
Most have respiratory gills in the mantle cavity
Feed using a food scraping radula
4 main classes
 Chitons: has segmented plates
 Gastropods: have a distinct head that usually has eyes and
sensory tentacles. Gastropods undergo torsion which is a
unique rearrangement of body parts. (snails)
 Bivalves: hinged two part shells. Adductor muscles hold both
valves together. (oysters, mussels, clams, etc.)
 Cephalopods: closed circulatory system, the smartest and
fastest group of mollusks. (squids, octopuses, and relatives)
Rotifers and tardigrades
 Tiny animals of damp or
aquatic habitats
 Rotifers- ciliated head
and pseudocoelom
 Tardigrades- (water
bears) have a reduced
coelom and molt
 Both can dry out and
survive for long periods
of adverse conditions
roundworms
 (Nematodes)
 Unsegmented body
 Molted cuticle
 Complete gut
 False coelom
 Some are human
parasites
Arthropods
 Largest phylum of animals
 Jointed exoskeleton
 One or more pairs of sensory antennae
in most
 Malpighian tubules- expel waste in
land-dwelling groups.
Arthropods
 Chelicerates- cephalothorax, abdomen, four pairs of
walking legs, eyes but no antennae. (horseshoe crabs and
arachnids)
 Crustaceans- mostly marine. Two pairs of antennae. (wood
lice, crabs, …)
 Myriapods- predatory centipedes and scavenging
millipedes. Many feet. Long body with similar segments,
pair of antennae, and two simple eyes.
 Insects- over a million species. Most diverse group of
arthropoda. Ants alone make up 10% of Earth’s biomass.
Three part body, head, thorax, and abdomen. Undergo
metamorphosis, the body form change between larval and
adult stages.
Echinoderms
 Invertebrates of the deuterostome lineage
 Skin with spines, spicules, or plates of
calcium carbonate.
 Adults are radial
 Water-vascular system- differentiated by
tubefeet
 eyespots
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