BILATERIA Flashcards
What are the key innovations of the group bilaterians?
Bilaterial symmetry Well-developed third body layer Compartmentalization Excretory organs Complete gut (mouth and anus)
Where do zoologists think the bilateral symmetry first arose?
In a benthic creeping form (planula-like)
What is cephalization?
Concentration of sense organs and nervous system at the anterior end
Describe the mesoderm layer of the bilaterians?
Fully cellular, usually extensive, and yields complex organs
Different tissues working together as a single unit (organ-system level of organization)
Describe the internal fluid-transport system of the bilaterians.
Fluid-filled cavities are fully enclosed and under control of organism and cavities may take on other functions
What are the two types of fluid-filled system of the bilaterians?
Ceolom (cavity lined by mesodermally derived epithelium)
Blood vascular system (channels in connective tissue =persistent larval blastocoel)
What is a pseudoceolom?
A blood vascular system lacking a heart
The excretory system of the bilaterians include 3 steps which are:
Ultrafiltration (typically across basal lamina)
Resorption (of ions and biomolecules)
Transport (move wastes out of body)
What are the two general forms of the nephridial system?
Metanephridia (large animals)
Protonephridia (small animals, primitive)
Describe the metanephridia.
Filtration occurs in a structure separate from resorption and transport. Depend on pressure differences for ultrafiltration.
Describe the protonephridia.
Filtration,resorption and transport all occur in one structure. Ultrafiltration is mainly by diffusion
What is the purpose of the anus in bilaterians?
Solely for digestion and absorption
What are the differences between the protostomia and the deuterostomia?
Origin of mesoderm is from different cell types (P: mesenchyme cells, D: epithelial cells)
Origin of coelom
Origin of mouth and anus
Type of Cleavage
What is the difference between the origin of mesoderm in the protostomes and the deuterostomes?
P: Mesenchyme (non-epithelial) migrate in
D: epithelial cells inpocket from archenteron
What is the difference in the mechanism of how the coelom originated in protostomes and deuterostomes?
D: Enterocoely outpockets from the archenteron close off and form enclosed, mesodermally lined coelom
P: schyzocoely: mesenchyme cells proliferate into balls of cells that split to form mesodermally lined coelom
