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Origins
All phyla form rather quickly in the “Precambrian explosion”
Before 500 MYA Common ancestry with fungi in a colonial
protistan similar to a choanoflagellate
Animals are heterotrophic by ingestion
I just love to ingest.
Store carbohydrate as Glycogen, or convert to fat
Have special cell to cell connections:
Tight junctions – seals between cells Gap junctions – communication between
cells Desmosomes -anchoring junctions Fig. 6.32 True tissues have these 4 Types of tissues
Most animals reproduce sexually
Only have 1 lifecycle!!
Mostly all diploid (2n)Except sperm and egg, with a few exceptions (e.g. drone bees etc.)
Asexual reproduction does happen in some lineages, but it is not common (e.g. aphids)
Animals Undergo Embryonic Development
Zygote – first new cell of animal– Diploid– Fertilized egg
Cleavage – – repeated cell division without growth– Same amount of cytoplasm divides into – More, smaller cells
Animals Undergo Embryonic Development
Blastula – hollow balls of cells not differentiated
Gastrula – diploblastic– Blastopore – Opening to outside– Archenteron- new “gut”
Cnidarians– Diploblastic & radially symmetrical
Embryonic tissue layers
Ectoderm Endoderm
Triploblastic animals also have: Mesoderm forms in between other two
layers.
Two Views of Animal Diversity
The traditional view based on body plan and embryonic development.
The new view is based primarily on molecular characteristics.
The Traditional View
Parazoa vs Eumetazoa Parazoa lack true tissues (special cell connections) Eumetazoa are all the other animals
Protostomates
Spiral and determinate cleavage-– Cell fate (specialization) starts during cleavage
Mesoderm forms from a ball then splits open to form a cavity (ceolom)
New opening forms an anus, blastopore becomes mouth.
Proto (first) stomate (mouth)
Deuterostomates
Radial and indeterminate cleavage-– Cell fate (differentiation) starts after cleavage– Identical twins
Mesoderm forms from pockets in endoderm. Always has a gap or cavity in side
New opening forms a mouth, blastopore becomes anus.
Deutero (second) stomate (mouth)
Protostome vs Deuterostome
I am a protostome. This opening will form my
mouth
I am a deuterostome
. This opening will
form my anus.
The New View
Parazoa vs Eumetazoa - same Radial vs. Bilateral - same Protostomate vs. Deuterostomate – still significant Aceolomate and Pseudoceolomate traits not as
significant. Considered simplified versions of ceolomates.
Groups Nematodes with Arthropods in one branch and the rest of the protostomates in another branch.
Metazoan phylogenies
Adoutte A. et.al. PNAS 2000;97:4453-4456
©2000 by The National Academy of Sciences
Lophotrochozoa
Protostomate Have Trochophore larvae –
– Bands of cilia
Also include the Lophophore phyla –– Ciliated feeding structure
Joins the Annelids – Mollusks onto the same clade
Larvae
Juvenile ( pre – reproductive) phase Have simpler morphology than adult Often move, and feed differently than adults
– Swims vs. crawls or flies
Often live in different habitats to avoid competing with adults
Often are the dispersal stage
Ecdysozoa
Based on molecular data Joins Nematodes and Arthropods Both groups have hardened exoskeletons
and undergo Ecdysis (Molting)
Molecular clades
Includes some aceolomates and pseudocelomates into the different clades
Not pre-ceolomates, but were rather simplified later.