Lecture 11: Cnidarian & Platyhelmenthes Flashcards
Embryonic Development
the development of a zygote and the emergents of a multicellular organism
zygote
diploid cell resulting from union of haploid gametes
embryo
young animal or plant while it is still contained within protective structure
Two major processes of Embryonic Development
Cleavage: first cell divisions in the embryo (one cell, two cells, 8 cells, morula)
Gastrulation: in-folding, invagination (forming about 2-3 embryonic tissue layers from the first layers of the cell) (morula, blastula, early gastrula, late gastrula)
Gastrula
have germ layers
Ecdoderm
outer layer of gastrula
- epidermis, nervous system`
Mesoderm
middle skin
- internal organs (muscles, skeletal systems, heart, stomach)
Endoderm
lining of digestive tract and respiratory system
Archenteron
“old gut”
- excretes enzymes into this space
blastopore
the opening of gastrula
- can be mouth or anus
Importance of gastrula
gives rise to tissue and gut
Types of symmetry
- Asymmetrical
- Radially symmetrical (along one plane)
- Bilaterally symmetrical (cut through eyes)
Cnidaria Characteristics
- jellyfish, corals, hydrozoans etc
- marine
- carnivorous
- diploblastic
- have nervous and muscular tissues
Cnidarian body forms
polyp (sessile), or medusa (motile)
- most life cycles include both forms
How do cnidarians get energy?
use cnidocytes to capture prey (inject them with venom), digest them in extracellular cavity
- in corals they get energy from symbiont; algae
Cnidarian nervous system
- get info from all directions
- little to no processing of info
- have direct lines of communication between sensors and effectors
Hydrozoa
polyp is dominant
- freshwater
- move by gliding
- ex. Portuguese man of war (have pneumatophores, cause life threatening reactions)
Scyphozoa
JELLYFISH!!!!!!
medusa is dominant, polyp is reduced
- have mesoglea (jelly like substance)
- eaten by leatherback turtles (i.e they cant feel the stings)
ex. cassiopeia (UPSIDE DOWN JELLYFISH!!!!)
- symbiotic relationship with algae
- tolerates low oxygen
- gets oxygen and nutrients from the algae
Anthozoa
polyp phase dominant (NO medusa at all)
ex. sea anemones
- retract tentacles in defence
- symbiotic relationship with anemone fish
ex. coral
- mutualistic relationship with zooxanthellae
- secrete CaCO3 (reefs)
Coral Bleaching
when coral expelled algae that live in their tissues
- colour fades over time
Protostomes
- blastopore develops into mouth
- have anterior brain
- ventral nerve cord
- triploblastic
Platyhelmenthes
FLAT WORMS!
- can be terrestrial or aquatic
- move by cilia
- have blind gut
- take up O2 and CO2 by diffusing it through their thin bodies
Cephalization
- linked to movement
- concentration of neurons and sensory structures at anterior end which allow them to feel for the environment
Sensory structures include:
- mechanoreceptors (touch)
- chemoreceptors (taste/smell)
- photoreceptors (light)
Platyhelminthes: Nervous system
- have longitudinal nerve cords
- have cerebral ganglion (concentration of neurons, “primitive brain”)
Turbella
- type of Platyhelminthes
- have a lot of stem cells (which allow them to regenerate)
- anterior end develops into head
- reproduce asexually by fission and sexually (hermaphroditic)
Monogenea
- ectoparasites
- have flat body with suckers that allow them to attach to host
Trematoda
- endoparasite
- go into blood vessels of intestine
- has primary host (someone that goes through sexual reproduction) and an intermediate host (shorter transitional stage)
Cestoda
- tapeworms
- endoparasite
- found in intestines of vertebrates
- have scolex (suckers/hooks)
- have proglottids (reproductive segments)
- no mouth or digestive system
- protective cuticle forms around embryos, terminal proglottids break off and are passed via feces
What is the advantage of a nervous system?
- movement around the environment (as compared to the sponge)
- allows you to latch onto things and make a new life.
