Lecture 3 Flashcards
features shared by all metazoans (multicellular animals)
presence of monoflagellated cells
mitotic aster apparatus
cell junctions
cells have special functions, communicate and cooperate
advantage of increased size
proteins associated with movement and other functions
include phylas: basal, lophotrochozoa, ecdysozoa and deuterostomia
evolutionary implications of multicellularity
reproduction
what it means to be an individual
advantage of increased size
distinguishing features of proiferans
porus = pore + fera = bearer
asymmetrical or radial symmetry
three cell types: pinacocytes, choanocytes (specific to sponges) and mesenchyme cells
body with central cavity or series of branching chambers
supporting structures - spicules (hard bits unique to sponges)
- spicule shape is relevant to taxinomy, protein based
no tissue or organs
use water filtration as a source of food
asexual reproduction: most common in freshwater forms, gemmules (overwintering forms) , amoeboid cells reorganize into sponge
sexual reproduction:
mostly monoecious (male and female function occurs in the same organism), asynchronous male/female function, choanocytes undergo meiosis and produce gametes, planktonic larvae
~9000 species
fourgroups recognized largely according to spicule characteristics
body wall complexity is not phylogenetically informative
distinguishing features of cnidarians
nettle
radial or biradial symmetry
diploblastic organization (2 embryonic layers)
gastrovascular cavity
nerve net
cnidocytes
> 9000 species, all mostly marine
four main groups
passive predators
incomplete digestive systems?
LIFE CYCLE
polyp/medusa stages
HYDROSTATIC SKELETON
- provides support and functions in movement
- fluid filled sheath
surrounded by muscle
distinguishing features of ctenophorans
comb jellies
diploblastic )possible triplo)
biradial symm
cellular mesoglia containing muscle cells
gastrovascular cavity with an anal opening
nerve net
eight cilia-bearing comb rows
colloblasts
monoecious
external fertilization
ciliated larvae
why might choanoflagellates be the sister group to the metazoans
group of protists …
structures of cnidocytes
embedded in the outer later of cnidarians
contains nematocysts (stinging capsules)
cnidocil ( hair like trigger on the surface of the cnidocyte)
describe cnidarian life history, including alternation of generations
medusa form releases egg which interacts with a sperm forming the zygote
zygote becomes a blastula–> swimming planula–> sesile planula
starts now colony by asexual budding
gastrozooid/hydranth develops
gonozooid forms which contains medusa buds
medusa forms emerge from the gonozooid
cnidarian: class hydrozoa
small, common, mostly marine
alternation of generations
cnidarian: class scyphozoa
marine, true jellyfish, medusa stage dominant
cnidarian: class cubozoa
tenticles suspended from corners of cuboidal medusa
Cnidarian: class anthozoa
marine, medusa absent, gastrovascular caity divided by mesentaries containing gonads/cnidocyte
four classes of Cnidarians
hydrozoa, scyphozoa, cubozoa and anthozoa
