An Introduction to Animal Diversity and Invertebrates

By Genetically Superior™

Common Characteristics of Animals

1. multicellular

2. no cell wall

3. heterotrophic eukaryotes

4. sexual reproduction

5. tissues develop from embryonic layers

Cambrian Explosion1. Occurred in the Paleozoic Era (542-251mya)

2. Animal diversification accelerates

3. Possible causes            a) new predator-prey relationships emerge that trigger natural                 selection                                 -forms of locomotive had to evolve (for predators) and shell defensees (for prey)

            b) 02 in atmosphere            c) evolution of the Hox Gene Complex provided developmental                 flexibility that led to variations

4. Arthropods begin to adapt to terrestrial habitats (example: millipedes and centipedes)

Cambrian Explosion    Neoproterozoic Era (1 bya-542mya)            -Generally accepted fossils of animals are only 575 mya              (known as Ediacaran fauna)

            -Related to cnidarians and corals, soft- Neoprotozoic bodied               molluscs

            -Numerous tunnels and tracks indicate forms of worms

       -570mya embryos discovered in China show basic structural         organization of present-day embryos (scientists not certain         which clade)                  

Embryonic Development 

1. most animals produce sexually

2. diploid stage dominates life cycle

3. zygote undergoes cleavage

Characterization of Invertebrates1. grade: group of animal species that share same level of organizational complexity2. body plans: a set of morphological and developmental traits that define a grade     

        a) symmetry                    -radial

                    -bilateral                                                

                

                                    - cephalization: bilaterally symmetrical animals (anthropods and mammals)                                        have trait of sensory equipment concentrated at anterior end

                                    - symmetry of animal fits its lifestyle

Diploplasts vs. triploblasts1.diploplasts

1. animals with two germ layers (endoderm and ectoderm)2. cnidarians3. jellies, corals

1.triploblasts1. three germ layers (third one being the mesoderm)2.  bilateral symmetry animals and cephalization

1. three categories of triploblasts based off of coeloms:2.  acoelomates3.  do not have coeloms

1. coelomates2. have a true coelom3. body cavity formed from mesoderm4. HUMANS!

1. pseudocoelomates2. have a false coelom3. body cavity formed from blastocoel 

Invertebrates

All Triploblasts

1.two ways of development of chordates (have spinal cord)

1.protostome development1.mouth develops from blastopore (opening of

gastrula)

1.deuterstome development1.anus develops from blastopore; 

           

Some Triploblasts are Chordates...

Chordates

Sponges (Porifera)-Are sessile (fixed in one place, immobile)

Symmetry:        -none

Diploplast:        -2 germ layers and no coelom

Cephalization:        -none

Special adaptations:        -unlike eumetazoans (all other animals), sponges lack true tissues        Examples:        -azure vase sponge (Callyspongia plicifera) 

CnidariansSymmetry:         -radial

Diploblast:         -2 germ layers and no coelom

Cephalization:         -none 

Special Adaptations:         -tentacles sting, thread punctures prey

Examples:         -jellies, sea anemones    

Hydrozoa: Man O' War

Flatworms    -In addition to many free living forms, some are also parasitic

Symmetry:    -bilateral

Triploblast:    -triploblastic development    -acoelomates (lack body cavity)

Cephalization:    -is evident (head ganglion attached to nerve cords)

Special Adaptations:    -Their flat shape/thin bodies enables gas exchange and elimination of nitrogen waste                 to occur through diffusion

Examples:

    

Tapeworm

Marine flatworm

Annelids (segmented worms)    -life cycle includes the trochophore stage (ciliated larval stage)  

Symmetry:        -bilateral

Triploblastic:        -3 germ layers       -pseudocoelomates

Cephalization:        -have some (pair of cerebral ganglia at their anterior end)

Special Adaptations:        -well-developed coelom provides a hydrostatic skeleton 

Examples:        -Earthworm        -Bristleworm    

Molluscs      -are soft-bodied animals, some have protective shell

    -four classes:             1. Polyplacophora (chitons)        2. Gastropoda (snails and slugs)        3. Bivalvia (clams, oysters, other bivalves)        4. Cephalopoda (squids, octopuses, cuttlefish, chambered nautiluses) Symmetry:        -depends upon the organism

Triploblasts:        -3 germ layers        -coelomates

Cephalization:         -is evident

Special Adaptations:         -share same body plans:            -foot (muscular, used for movement)         -visceral mass (contains most internal organs)        -mantle (fold of tissue that drapes over visceral mass and secretes a shell if one is         present)

Nemotodes (round worms)        -most are parasitic

Symmetry:        -bilateral

Triploblastic:        -3 germ layers        -pseudocoelomates

Cephalization:        -some (only two small anterior “cerebral” ganglia from which neural chords          split)

Special Adaptations:        -digestive system is complete (has both anus and mouth)        -can redirect some cellular functions of their host

Examples:        -Parasitic Trichinella spiralis   

Echinoderms        -slow moving or sessile marine animals  Symmetry        -radial as adult (not perfectly), bilateral as larvae

Triploblastic:        -3 germ layers        -coelomates

Cephalization:        -none  

Special Adaptation:        -water vascular system (tube-like extensions that function in locomotion,              feeding, and gas exchange)

Example:        -star fish        -sea urchin

Arthropods (insects, arachnids, crustaceans)  Symmetry:        -bilateral

Triploblastic:        -3 germ layers        -coelomates 

Cephalization:        -is extensive (concentration of diverse sensory structures at the anterior          end)

Special Adaptations:        -hard, external shell (exoskeleton or cuticle) and the molting process

Examples:        

Grasshoppers

        

Arthropodscoelomates

Earthworms                coelomates

Annelids