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Chapter 32
Characteristics that Define Animals
 Nutritional modes
 Ingest organic molecules and digest them via enzymes
 Cell structure and specialization
 Multicellular with structural proteins (collagen) for support
 Muscle and nervous tissue to send signals and allow mobility
 Reproduction and development
 Reproduce sexually with diploid (2n) stage as dominating
 Born to resemble adult or as larva that undergoes
metamophosis
 Genes regulate expression of other genes

Homeoboxes, common DNA sequences, known as Hox genes
Embryonic Development
 Cleavage, rapid cell divisions without significant
growth
 Creates a similar sized blastula, or hollow ball of cells
 Gastrulation results from inward folding of the embryo
 Produces layers of embryonic tissue, endo- and ectoderm
 Layers develop into adult structures
Symmetry
 Asymmetry
 Most sponges
 Radial symmetry
 Top and bottom, but no front,
back, or sides
 sessile
 Bilateral symmetry
 Anterior (front) and posterior
(back), dorsal (top) and
ventral (bottom)
 Most demonstrate
cephalization

Sensory structures anteriorly
 Motile with complex
movements
Tissues
 True tissues are collections of specialized cells isolated
from others by membranous layers
 Sponges lack true tissues
 Gastrulation forms embryonic layers of tissue, called germ
layers
 Ectoderm covers outer part of embryo
 Outer layer or animal and some nervous systems
 Endoderm forms innermost layer
 Lines developing digestive tube or archenteron, becomes digestive
tract lining, liver, and lungs
 Diploblastic animals, i.e. cnidarians and comb jellies
 Mesoderm in all animals with bilateral symmetry
 Muscles and most other organs
 Triploblastic animals, i.e. flatworms to arthropods to vertebrates
Body Cavities
 Presence of absence classifies bilateral
(triploblastic) animals
 Space separating digestive tract from
outer body wall, called a coelom
 Coelomates
 All mesoderm, joined dorsally and
ventrally
 Pseudocoelomates
 Formed from endo- and mesoderm
 Acoelomates
 Lack a body cavity
 Allows independent organ movement,
protects, and forms a fluid skeleton
Protostomes and Deuterostomes
 Cleavage
 P: spiral cleavage, planes of division are diagonal;
determinate cleavage, fate of each cell determined early
 D: radial cleavage, planes parallel or perpendicular;
indeterminate cleavage, each cell retains capacity to develop
 Coelom formation
 P: solid masses of mesoderm split to form
 D: mesoderm buds from archenteron
 Blastopore fate
 P: mouth before anus
 D: anus before mouth
Kingdom Animalia Hypotheses
 35 phyla currently recognized
 Grouped through shared-derived characteristics into
clades
 What does this mean?
 ‘Traditional’ morphological character
 Molecular data based on DNA has provided new
hypotheses
 ‘New’ molecular sequences data
 Two hypothesis have several points of agreement
Major Defining Features
 All animals share a common ancestor
 Kingdom animalia is monophyletic
 Sponges are basal animals
 Branch from base of both trees
 Eumetazoa is a clade of animals with true tissues
 Basal members are diploblastic with radial symmetry
 Most animals form a bilateria clade
 Bilateral symmetry and 3 germ layers
 Chordates form a deuterostomia clade
Disagreements
 Morphological has bilaterians as 2 clades
 Protostomes and deuterostomes

Arthropods and annelids are protostomes with segmented bodies
 Molecular has bilaterians as 3 clades
 Deuterostomia


Arthropods and annelids not related
Group of acoelomate flatworms not represented in morphological
hypothesis

Basal bilaterians, not phylum platyhelminthes
 Lophotrochozoa


Lophophore develops, crown of ciliated tentacles for feeding
Distinctive trochophore larva stage
 Ecdysozoa are animals that secrete exoskeletons

Ecdysis, molting old exoskeleton
Morphological vs Molecular Trees