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Lecture 19

BIO SCI 94 Lecture Notes - Lecture 19: Ecdysozoa, Great Salt Lake, Microfabrication

Biological Sciences
Course Code
Brandon Stuart Gaut

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Lecture 19: Protostomes & Deuterostomes
Protostomes vs. Deuterostomes
Diploblast vs triploblast
Protostomes: Lophotrochozoans vs. Echdysozoans
o Lophotrochozoa: feeding structure (lophophore), larval type (trocophore), & special embryonic
cleavage; grow incrementally
o Molluscs
Bivalves (clams, mussels): suspension feeders that have lost the radula
Gastropods (snails & slugs)
Cephalopods (squids, octopi)
Modular body plan - foot, visceral mass, mantle
o Ecdysozoa: grow by molting
Bilateral vs. radial symmetry
*From Prof. Gaut's slides
o All Ecdysozoans grow by molting: process of shedding an external cover
o When the cover is hard, it's an exoskeleton; otherwise, it's called a cuticle
o Segmentation
o Grow within the exoskeleton & shed exoskeleton to grow bigger
o Nematodes are Ecdysozoa
Ecdysozoans: Arthropoda
o Have segmented (or modular) body plans - hox genes
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o Segmentation arose a few times in the evolution of animals: in the arthropods, chordates, &
annelid worms
o Annelids and Arthropods were once thought to be closely related b/c they both have
segmented body plans
o Segment specialization
o Jointed appendages
o Exoskeleton or cuticle
>1 million species named
>500 my old
Very prominent in the fossil record
o Going back to the Cambrian Explosion & before
Early arthropods show little variation between segments
It's thought one advantage of segmentation is diversification via new segments co-opted for new
Arthropods go through metamorphosis: refers to a drastic change from one developmental stage to
*From textbook
o Arthropods aren't the only ones to go through metamorphosis but it can be especially dramatic in
arthropods & especially insects
o Larva - immature stage
o 2 types of metamorphosis:
Incomplete: when the juvenile (or nymph) stage looks similar to the adult stage & eats the
same food source
Complete: occurs when embryogenesis (formation & development of an embryo) produces a
larval form that often differs dramatically from the adult form --> that larva becomes a pupa,
which is then remodeled into an adult
e.g. mosquitoes, butterflies
Complete metamorphosis is 10x more common than incomplete
o Note about animal life cycles:
o Most animals have diploid-dominant life-cycles b/c the haploid stage is relatively short-lived
& often single-celled (think of sperm & eggs in human development)
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