chapter 27: introduction to animal diversity

features of the animal kingdom

-multicellular eukaryotes - many have complex bodies

-heterotrophy

-active movement

-reproduction

-embryonic development

-body plan

cells joined together

by: protein-rich extracellular matrix (ECM) with collagen (protein unique to animals), protein junctions

internal organ systems

most animals have integrated organ systems, exchange chemicals with external environment, maintain internal homeostasis through feedback mechanisms, if key system fails, animal dies

ingestive heterotrophs

most animals are ingestive heterotrophs (but some parasites are absorptive!)

somatosensory and motor

most animals have nerve cells (neurons) & muscle cells, unique to animals, sensory receptors detect stimulus, motor response produces movement

sensory neuron --> interneuron --> motor neuron --->muscle

sexual reproduction

animal life cycle in almost all, most: separate sexes (but sex may change) some: hermaphroditic

hermaphroditic

an organism that has both male and female reproductive organs

asexual reproduction

animal life cycle in some, fragmentation & regeneration

budding, rare: parthenogenesis

parthenogenesis

virgin females produce eggs that develop into offspring

ploidy

diploid life, except sperm & egg, (except some: all males are haploid!)

larval stage

most animals have a larval stage before adulthood, larva differs in form, function & often habitat from adult (often a dispersal stage), goes through metamorphosis to adult form

embryonic development

most animals have similar genes that control development, including "Hox" genes, zygote --> cleavage --> blastula stage

blastula

the hollow ball of cells marking the end stage of cleavage during early embryonic development

gastrula

an embryonic stage in animal development occurring because of gastrulation, encompassing the formation of germ layers (origin of tissues)

blastospore

the first opening made during gastrulation

archenteron

the endoderm-lined cavity, formed during gastrulation, that develops into the digestive tract of an animal

diploblastic

animals with 2 germ layers, endoderm and ectoderm

ectoderm

the outer germ layer that develops into skin and nervous tissue

endoderm

the inner germ layer that develops into the lining of the digestive and respiratory systems (internal organs)

triploblastic

animals with 3 germ layers, ectoderm and mesoderm and endoderm

mesoderm

middle germ layer; develops into muscles, and much of the circulatory, reproductive, and excretory systems

protostomes

the coelom forms from splits in the mesoderm, the mouth forms from the blastopore

deuterostomes

the coelom forms from mesodermal outpocketings of the archenteron, the mouth forms from a secondary opening, the anus develops at the site of the blastopore, ex: humans

protostome development

embryonic development where cleavage is spiral and determinate, early embryonic cells "fated" to become certain body parts, lose any early cell results in defect or death

spiral cleavage

planes of cell division are at oblique angles to the axis of embryo

deuterostome development

embryonic development where cleavage is radial and

indeterminate, any early cell can become complete organism

radial cleavage

planes of cell division are parallel or perpendicular to the axis of embryo

body plans

general structure of an animal, the arrangement of its organ systems, and the integrated functioning of its parts

body plan features

-symmetry

-body cavities

-segmentation

-presence and function of appendages

radial symmetry

arrangement of body parts around a central axis, usually sessile (attached) or planktonic (drifting) life, no left and right sides, nor front or back, equips sea creatures to experience the environment equally from all directions

bilateral symmetry

a bilateral animal has two axes of orientation: front to back and top to bottom, usually w/ "head" = concentration of sensory organs at anterior (cephalization), active lifestyle

coelom

body cavity, fluid-filled space between body wall and digestive tract, cushions internal organs, allows internal organs to grow and move independently of the outer body wall

true coeloms

most body cavities, completely surrounded by the mesoderm, forms from tissue derived from mesoderm

pseudocoeloms

a body cavity that is formed from mesoderm and endoderm

acoelomates

no body cavity

hox genes

series of genes that controls the differentiation of cells and tissues in an embryo, determine body plan, segmentation, number and placement of appendages etc,

hox genes characteristics

highly conserved genes, encode transcription factors, in vertebrates, the genes have been duplicated into four clusters: Hox-A, Hox-B, Hox-C, and Hox-D, genes within these clusters are expressed in certain body segments at certain stages of development

one common ancestor of animals

choanoflagellates are closest protist group to animals, first animals were sponge-like (710 mya?)

proterozoic (pre-cambrian) animals

ediacaran biota, ~565mya, earliest known animal fossils; many extinct! soft-bodied: sponges; jellyfish-like; worm-like

paleozoic era animals

"Cambrian explosion" ~535 mya, dramatic animal diversification, almost all major phyla (+ other extinct ones)

first mineralized skeletons, shells

later paleozoic era

vertebrate fishes dominate seas, arthropods invade land, later vertebrates invade land (amphibians), finally first reptile-like amniotes

mesozoic era animals

dinosaurs, pterosaurs, aquatic reptiles, origin of birds and mammals

cenozoic era animals

diversification of modern groups

extinctions

mass extinctions have occurred repeatedly over geological time

animal phylogeny based on

-analyzing whole genomes

-morphological traits

-ribosomal RNA (rRNA) genes

-hox genes

-protein-coding nuclear genes

-mitochondrial genes

inferences from the animal phylogenetic tree

-all animals share a common ancestor

-sponges are the sister group to all other animals

-eumetazoa is a clade of animals with tissues

-most animal phyla belong to the clade Bilateria

3 major clades of bilaterian animals

deuterostomia, lophotrochozoa, and ecdysozoa