Ls1: Animals Part I

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KEY CONCEPTS
- Animals are very species rich and morphologically diverse lineage of multicellular organisms

Back 1

they are key consumers and humans depend on them fro transportation, power, or food.
34 phyla and 10million + species

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KEY CONCEPTS
- Major groups of animals are defined by design and construction of their basic body plan, which
differs in numbers of embryonic tissues, symmetry, presence or absence of coelom, and way in which early events in development proceeds

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- Sponges are the only asymmetric animals and lack tissues
- Cnidarians and Ctenophores: radial symmetry and diploblastic
- A few are bilateral, three layers, but no coelom
- Majority of animal species are bilateral, triploblastic, and coelom →tube-within-a-tube: protostome/deuterostome

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KEY CONCEPTS
- Two protostome groups and deuterostomes
- Sponges are most ancient living animals
- Choanoflagellates are the closest living organisms

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- triploblasty, bilateral symmetry, coelmons, protostome/deuterostome development evolved just once
- pseudocoelems evolved independetly
-segmented body plans arose at least three times independently

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KEY CONCEPTS
- Within major groups of animals, diversification depended on movement and feeding methods
- most animals get nutrients by eating other organisms
- all animals must move on their own at some point in life

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- wide variety of feeding strategies
- most animal movements based on muscle contractions
- one of three type of skeletons: hydrostatic, endoskeleton, exoskeleton
- all appendages may be homologous

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Animals are Consumers

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they occupy the upper levels of food chains in both acquatic and terrestrial habitats

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Animal Traits

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- no cell walls, but extensive extracellular matrix
- only lineage with muscle and nerve tissue
- no alteration of generations
- adults of most species are diploid and only haploid gametes

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Morphological Diversity in Animals

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based on differences in
- mouth for eating
- limbs for moving

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ANIMAL BODY PLAN
Defining Features

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- number of embryonic tissue layers
- type of body symmetry/degree of cephalization
- fluid-filled cavity present or absent
- how earliest events of embryo development proceeded

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EVOLUTION OF TISSUES
Tissues

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tightly integrated structural and functional unit of cells

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Epithelium

Back 10

layer of tightly joined cells that covers body surface

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Diploblasts

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animal whose embryos have two germ layers: ectoderm and endoderm

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Triploblasts

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animal whose embryos have 3 germ layers:
- ectoderm→skin
- mesoderm→muscles, organs
- endoderm→gut

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SYMMETRY AND CEPHALIZATION
Asymmetry

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sponges, no symmetry

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Radial Symmetry

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at least 2 planes of symmetry

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Bilateral symmetry

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- single plane of symmetry
- allowed cephalization

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Cephalization

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development of head allowed:
- feeding
- sensing environment
- processing information

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BODY CAVITY
Coelem

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- fluid filled body cavity as a container for circulation of oxygen and nutrients
- acts as hydrostatic skeleton

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Acoelomates

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Have no coelom

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Pseudocoelomates

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- Coelom forms between endoderm and mesoderm
- muscle and blood vessels can form on either side of coelem
- ex: roundworms and rotifers

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Coelomates

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- Coelem forms from mesoderm (two hollows)

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Hydrostatic Skeleton

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acts like water ballloon and allows soft-bodied animals to move without fins or limbs
- body wall creates pressure in fluid
- fluid filled pseudocoelem creates tension in body wall
- muscles cause shape change

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PATTERNS OF DEVELOPMENT
Bilateria

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- includes all coelomates except ADULT echinoderms
- three embryonic tissue layers
- bilaterally symmetric
- 2 groups: protostomes and deuterostomes

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Cleavage

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rapid series of mitotic divisions that occurs in the absence of growth

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Gastrulation

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series of cell movements that results in formation of embryonic tissue layers (endoderm, mesoderm, ectoderm)

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Protostomes
"first mouth"

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- arthropods, mollusks, and annelids
- Cleavage: spiral
- Gastrulation: pore becomes mouth
- Coelom formation: solid mesoderms hollow out

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Deuterostomes
"second mouth"

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- Chordates and echinoderms
- Cleavage: radial
- Gastrulation: pore becomes anus, mouth forms later
- Coelom formation: mesoderm pockets pinch off gut

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Tube-within-a-Tube design

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outer tube = body wall
inner tube = gut

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MOLECULAR PHYLOGENIES
Major groups of animals characterized by:

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- variation in embryonic tissues
- body symmetry
- type of body cavity
- early development

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Choanoflagellates

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group of PROTISTS that is the closest living relatives of animals

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Porifera
(Sponges)

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- most basal animal phylum
- like choanoflagellates:
- sessile
- filter feeders by feeding cells called choanocytes

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Putting the phyla in order

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- Multicellularity
- Diploblasty
- Radial Symmetry
- Bilateral symmetry and cephalization
- Triploblasty
- Protostome development
- Pseudocoelom
- Coelem
- Deuterostome development and segmentation independently
- radial symmetry and segmentation again independently

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Segmentation

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type of body architecture that evolved independently in both protostomes and deuterostomes

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Vertebrates

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- animals with skulls and usually backbones
- monophyletic

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Invertebrates

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- animals that are not vertebrates
- paraphyletic

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DIVERSIFICATION OF ANIMALS

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- within each phylum, the basic features of the body plan do not vary from species to species
- diversification of species within each lineage was in most cases triggered by the evolution of innovative methods for FEEDING and MOVING

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Feeding:
3 general food sources

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1. plants and algae
2. other animals
3. detritus

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Feeding:
4 general methods

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1. suspension/filter feeders
2. deposit feeders
3. fluid feeders
4. mass feeders

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Suspension Feeding

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- capture food by filtering particles suspended in water or air
- mollusks: clam siphons have cilia and gills
- chordates: Baleen whales
- arthropods: krill

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Deposit Feeding

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- eat their way through substrate
- digest organic matter in the soil/sea floor
- simple mouthparts and worm-like body shape
- herbivores, parasites, detrivores

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Fluid Feeders

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- suck or mop up liquids: blood, nectar, fruit juice, plant sap
- mouthparts for piercing

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Mass Feeders

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- take chunks of food into mouth
- structure depends on food consumed

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Movement
3 functions in adults

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1. find food
2. find mates
3. escape from predators

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Limbs: Unjointed

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- sac-like

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Limbs: Jointed

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- fast, precise movements possible
- prominent in vertebrates and arthropods

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Reproduction and Life Cycles

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- some species: asexually and sexually
- fertilization can be internal or external

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Vivaparous

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eggs/embryos stay in female's body during development
- mammals, few sea stars species, onychophorans, fish, lizards

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Oviparous

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eggs laid outside to develop independently
- majority of animals

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Ovoviviparous

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female retains egg inside during early development, but growing embryos are nourished by yolk inside egg and not by nutrients transferred from the mother

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Homometabolous metamorphosis
aka
complete metamorphosis

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larva → encased pupa → adult

ex: most insects, marine animals
ex: most cnidarians have largely sessile polyp and alternates with free floating medusa

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Hemimetabolous Metamorphosis
aka
Incomplete Metamorphosis

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Juvenile nymph looks like a mini adult

ex: grasshopper

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basal groups

PORIFERA
(Sponges)

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- benthic: live at the bottom of aquatic environments

BODY:
- body is system of tubes and pores: channels for water currents
- assymetric
- specialized cell types and epithelial tissues

FEEDING: suspension

MOVEMENT: sessile adults and flagella swimming larvae

REPRODUCTION:
-totipotent: isolated cell can grow into adult
- sexual reproduction capable

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basal groups

CNIDARIA
(Jellyfish, Corals, Anemones, Hydroids, Sea Fans)

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BODY:
- radially symmetric
- diploblast

FEEDING:
-cnidocyte (feeding structure) like tentacles that have nematocyst (barbed and spearlike coated with toxin)
-only one opening for feeding and excretion

MOVEMENT:
- Polyp form: muscle cells at base that contract
- Medusa form: jet propulsion

REPRODUCTION:
- asexual: fragmentation, budding, and fission
- sexual: gametes released from mouth and external fertilization in open water

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basal groups

CTENOPHORA
(Comb Jellies)

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BODY:
- transparent and ciliated and gelatinous
- diploblasts
- planktonic (life near surface)

FEEDING:
- predators

MOVEMENT:
- beating cilia in comblike rows down length of body

REPRODUCTION:
- most are bisexual and self-fertilize
- external fertilization → free swimming larvae

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basal groups

ACOELOMORPHA
(small worms that live in mud/sand)

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BODY:
- bilaterally symmetric
- distinct anterior and posterior ends
- triploblastic but NO COELOM

FEEDING: detritus or prey on small animals/protists

MOVEMENT: swim, glide, burrow with aid of cilia

REPRODUCTION:
- asexual: fission
- sexual: bisexual and internal fertilization with eggs laid outside