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Lecture 18

BIO SCI 94 Lecture Notes - Lecture 18: Protostome, Symmetry In Biology, LophotrochozoaPremium

Biological Sciences
Course Code
Brad Hughes

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Major human food source
Provide pollination/soil preparation to ecosystem
Includes insects protect/damage crops
Provides materials like silk, pearls
Many important ecological roles
Live in every aquatic/terrestrial habitat
Can be detritivores, herbivores, or carnivores
Ecological important extend to human health
Common parasites, transmit human disease
Include two most important model organisms
The fruit fly Drosophila melanogaster
The roundworm Caenorhabditis elegans
What is a Protostome?
Two major groups of bilaterally symmetric, triploblastic animals: protostomes and
During gastrulation→ pore forms→ becomes mouth
Cavities rise from blocks of mesodermal cells→ coelom forms
Phylogenetic studies support hypotheses- protostomes monophyletic
Protostome developmental sequence rose once
DNA sequence data support two major subgroups
Lophotrochozoa- include mollusks, annelid worms
Ecdysozoa, arthropods
The Water to Land Transition
Fossils imply protostome come from ocean
Protostome transition from sea to land
Transition occurred many times as protostomes diversified
Water to land transition important- open new habitats, new resources
Transition to land: necessary adaptation for protostomes to
Exchange gases
Avoid drying out
Hold up their bodies under their own weight
Terrestrial protostomes adapted to solve challenges
Roundworms/Earthworms- high surface-area to volume ratio
Increases efficiency of gas exchange across body surface

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Some arthropods/mollusks have gills/other respiratory structures within
Insect have waxy layer- minimizes water loss
Environment dries→ Open respiratory passages will be closed
Desiccation-resistant eggs adapted many times in population→ transition
to land life
Insect eggs- thick membrane→ keeps in moisture
snail/slug eggs- thich shell→ keeps water
Modular Body Plans
Morphological.physiological diversification-genetic basis
Wrongly assumed different organisms need different genetic instructions
Multicellular animals- common tool kit of genes→ creates animal body
plan during development
Hox genes important in tool kit
Express genes in tool kit at different time/place→ differences
Generation of new genes→ diversification of animal body plan
Change expression pattern of existing genes- huge impact on animal body plan
Compare diverse organisms in lineage, genetically base modularity evidence
Small set of elements reused/rearranged→ produce many different
What Is a Lophotrochozoan?
Name inspired by presence of:
Lophophore- feeding structure
Trochophore- type of larva
Lophotrochozoans show spiral pattern cleavage during embryonic development
Lophophore- specialized structure, rings mouth of animals, functions in
suspension feeding
Trochophores- type of larva, common to phyla of lophotrochozoa
Trochophore larva- ring of cilia around middle, functions-
Trochophore larvae→ metamorphosis
Hypothesis- adaptation for larvae of sessile adults to spread to new
Phylogenetic analysis reveal spiral cleavage is synapomorphy for
Spiral cleavage- During early embryogenesis,cells divide at oblique angles
→ blastula forms
Evidence animals to Lophotrochozoa:
Has lophophore
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