Chapter 32

Characteristics that Define AnimalsNutritional modes

Ingest organic molecules and digest them via enzymesCell structure and specialization

Multicellular with structural proteins (collagen) for support

Muscle and nervous tissue to send signals and allow mobility

Reproduction and developmentReproduce sexually with diploid (2n) stage as dominatingBorn to resemble adult or as larva that undergoes

metamophosisGenes regulate expression of other genes

Homeoboxes, common DNA sequences, known as Hox genes

Embryonic DevelopmentCleavage, rapid cell divisions without significant growthCreates a similar sized blastula, or hollow ball of cellsGastrulation results from inward folding of the embryo

Produces layers of embryonic tissue, endo- and ectodermLayers develop into adult structures

SymmetryAsymmetry

Most spongesRadial symmetry

Top and bottom, but no front, back, or sides

sessileBilateral symmetry

Anterior (front) and posterior (back), dorsal (top) and ventral (bottom)

Most demonstrate cephalization Sensory structures

anteriorlyMotile with complex

movements

TissuesTrue tissues are collections of specialized cells

isolated from others by membranous layersSponges lack true tissuesGastrulation forms embryonic layers of tissue,

called germ layersEctoderm covers outer part of embryo

Outer layer or animal and some nervous systemsEndoderm forms innermost layer

Lines developing digestive tube or archenteron, becomes digestive tract lining, liver, and lungs

Diploblastic animals, i.e. cnidarians and comb jelliesMesoderm in all animals with bilateral symmetry

Muscles and most other organs Triploblastic animals, i.e. flatworms to arthropods to

vertebrates

Body CavitiesPresence of absence classifies

bilateral (triploblastic) animalsSpace separating digestive tract

from outer body wall, called a coelom

CoelomatesAll mesoderm, joined dorsally and

ventrallyPseudocoelomates

Formed from endo- and mesodermAcoelomates

Lack a body cavityAllows independent organ

movement, protects, and forms a fluid skeleton

Protostomes and DeuterostomesCleavage

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 formationP: solid masses of mesoderm split to formD: mesoderm buds from archenteron

Blastopore fateP: mouth before anusD: anus before mouth

Kingdom Animalia Hypotheses35 phyla currently recognizedGrouped through shared-derived

characteristics into cladesWhat 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 FeaturesAll animals share a common ancestor

Kingdom animalia is monophyleticSponges are basal animals

Branch from base of both treesEumetazoa is a clade of animals with true tissues

Basal members are diploblastic with radial symmetry

Most animals form a bilateria cladeBilateral symmetry and 3 germ layers

Chordates form a deuterostomia clade

DisagreementsMorphological has bilaterians as 2 clades

Protostomes and deuterostomes Arthropods and annelids are protostomes with segmented

bodiesMolecular 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