Quiz 2 - Bilaterians Flashcards
What are bilaterians called
Triploblast animal neither a proto nor a deuter
What is metamery
Mesodermal event
Serial repetition of unit subdivisions of ectoderm and mesoderm
NOT endoderm
What animals show metamery in bilaterians
Annelids
Arthropods
Chordates
What is the step-by-step hypothesis of bilaterian evolution
Planuloid-acoeloid hypothesis
What is the archicoelomate hypothesis
Fast transition to complex, but then simpler things lost those traits later on
What are 4 possible urbilaterians?
Micro, acoel, turbellarian-like worm w cilia locomotion + direct dev
Micro, acoel or pseudo, pelagic
Macro, coelomate, benthic + segmented larva stage
Micro larva w cilia + macro adult coelo w filter feeding adult
What are the 5 bilaterian innovations
Bilateral symmetry
Third tissue layer - triploblasts
Compartmentalization
Excretory organs
Complete through gut
If bilateral symmetry came from a benthic form, then it would pre-date the origin of directed locomotion - what is the alternative hypothesis for bilateral symmetry in bilaterians
Bilateral symmetry evolved to make internal circulation better by compartmentalizing the gut and major ciliary tracts
What tissue layers contains the GI tract, auditory, respiratory ?
Endoderm
What tissue layer contains the mesenchyme, muscles, cartilage, bone, blood + tissue layers?
Mesoderm
What is mesenchyme
Connective tissue + lymphatic + circulatory system (lymph + blood)
What tissue layer is the nervous system of bilaterians in?
Ectoderm
Why did bilaterians require compartmentalization
Large body size + extensive mesoderm needed internal fluid filled cavities that are enclosed + controlled
House gonads + locomotion control
Large body size + extensive mesoderm required a good excretory system. Explain ultrafiltration, reabsorption, and transport in bilaterian excretory systems
Ultrafiltration - across basal lamina (point of aatached for other cell types + permeability barrier for urine)
Reabsorption - ions + valuable biomolecules
Transport - move waste out of body
What is a complete through gut
Mouth and anus
Acoelomate have no body cavity, which means their organs are in direct contact with the epithelium… but what holds the organs in place?
Semi-solid mesodermal tissues btw the but and the body wall
Pseudocoelomate are called false cavities… how are they organized
Tissue from mesoderm partially line fluid filled body cavity
True coelomates = eucoelomates - with a complete lining called the… ?
Peritoneum
Organs are completely attached
Libbie hymans idea about body cavities and complexity ?
Difference btw body cavity grades does NOT reflect complexity
What are phylum xenacoelomorpha
Acoel
Marine sediments, some can swim
No gut, no excretory system, extracellular matric
Why are xenacoelomorphs thought to maybe be the first bilaterian
Acoel - no cavity
No gut, no excretory system, extracellular matrix
Has nerve net + statocysts - early nervous system
No mouth or pharynx - needs endosymbionts like green algae
Fewer than 8-10 hox genes - more similar to bilaterians than cnidarians - thought to be have duplicated before proto/deuter split
Who is the wanderer of the phylogenetic tree
Xenoturbella
Describe xenoturbella
Free living, yellow worm, flattened ventrally
A-P + D-V axis, longitudinal grooves
Name all the phyla that xenoturbella has been placed under in the phylogenetic tree
Acoelomorpha bc simple body plan + cilia
Hemichordata + echinoderm - nerve net + epidermal ultra structure
Was under mollusc but because it consumed eggs of bivalves
Why were xenoturbella classified with mollusks
Found similar dna, but it was because xenoturbella eat molluscs, so contaminated dna
What do hox genes determine
Anterior posterior axis
How do xenoturbella hox genes compare to the hypothetical proto/deuter ancestor
Fewer hox genes
Why is xenoturbella significant for determining bilaterian evolution
Help explain bilaterian symmetry and mesoderm
Whats the second possible bilaterian ancestor
Myxozoa
Whats the difference between endo and extoparasites
Endo - live within another organism
Ecto - live on another organism
Parasites are simple and degenerate possibly evolving towards reduced structural complexity
What are the closest free living relatives to parasites - who has the most described parasitic species
Nematoda and arthropoda
What is the third possible bilaterian ancestor
Orthnectida
What phyla are endoparasites of turbellarians, polychaetes, gastropods, molluscs, brittle stars
Orthonectida
Why would orthonectida be possible ancestors of bilaterians?
Endo parasitic
Bilateral in some development stages
No gut, hemal system (blood), nephridia or neurons
Epidermis for moving + nutrient uptake (simple)
Why is difficult to classify phylums
Hard to see how the groups are related to one another
What is characteristic that is strictly deuterstome
Gill slits
What is ther difference btw radial and spiral cleavage
Radial - parallel / right angle to polar axis
Spiral - oblique to polar axis
Why was the ancestral trait likely radial cleavage?
Only one major switch to spiral in platyhelminthes and mollusks and annelids
What schizocoely?
Mesenchymal cells proliferate into balls of cells
They split to form mesodermally lined coelom
What is enterocoely?
Outpockets from archentron (primary gut formed in gastrolation and then makes the mesoderm and the endoderm) close off and make enclosed mesodermally derived coelom
How is the fate of cells following the earliest cleavage different in proto than deuter
Proto - determinate
Deuter - indeterminate
How is the cleavage pattern different in proto than deuter
Proto - spiral
Deuter - radial
How is the fate of the blastopore different in proto than deuter?
Proto - mouth first
Deuter - anus first
How is the formation of the coelom different in proto than deuter?
Proto - splitting if mesoderm (schizocoely)
Deuter - out-pocketing of mesoderm (enterocoely)
Chaetognatha are important for the food web because ….
Predators of zooplankton
What do chaetognatha look like
Slender, shaft bodies, horizontal fins
What do cheatognatha have for hunting on the sides of their head
Hooked chitinous grasping spines
Why were chaetognatha previously thought of as deuterstomes?
Radial cleavage Blastopore Coelom formation Tripartite body Excretory Circulatory Cicular muscles
What has a nervous system w cerebral ganglia + small eyes for light detection?
Chaetognatha
What kind of development do chaetognatha have?
Direct
Chaetognatha were thought to be related to deuterstomes… are they?
Currently with protostomes
Why are chaetognatha so important to understand?
Evolution of morphological characters
Reconstruction of last common ancestor
Early develolmeng resembles radial cleavage
