phylum cnidaria Flashcards
habitats and lifestyle: cnidaria
- marine and freshwater
- benthic and pelagic
- solitary and colonial
- two structures/modes: polyp and medusa
- ALL predators (corals photosynthetic and predators)
two body forms of cnidaria
polyp and medusa
polyp = tentacles up
medusa = tentacles down
example of polyp and solitary
anemone
example of polyp and colonial
coral
example of medusa and solitary
jellyfish
example of medusa and colonial
portuguese man of war
outside layer of anemone
epidermis
layer inside the epidermis (anemone)
gastrodermis
what is between epidermis and gastrodermis and what is it composed of ?
mesoglea - comprised of collagen and extracellular matrix
cnidaria: major characteristics
- true internal gut
- diploblastic - two embryonic cell layers (ectoderm and endoderm - no mesoderm)
- nerve net, w nerve plexuses but NO central brain
- have cnidocytes - which have nematocysts (stinging cells)
- some have alternation of generations between polyp and medusa forms (asexual and sexual forms)
- bilateral symmetry
how do cnidocytes work?
cnidocytes have nematocysts which are stinging cells
they are stored inside out and triggered mechanically by a cnidocil. when triggered, will release thread and barb to increase surface area of stinging
the increased surface area helps to increase the amount of transmission of toxins
alternation of generations in cnidaria
sexual and asexual phase, physically separated - like 2 different animals but not
adult medusa stage can reproduce sexually. these adult male and female produce egg and sperm which are halpoid. when fertilization happens, it is back to diploid
cnidarian cell types
epitheliomuscle cells
nerve cells
cnidocytes
gland cells
interstitial cells
cnidarian life cycle - hydrozoans
polyps reproduce asexually by budding off medusae, and then medusae give rise to polyps by sexual reproduction
when polyp strobilates — segmenting its body to reproduce — it releases tiny ephyra into the water which grow into adult jellyfish
what is considered a coelom ?
defined by being enclosed in mesoderm — therefore cnidarians cannot have a TRUE coelom bc dont have mesoderm
are coelentrata coelomates ?
no, dont hv enclosed coelom by mesoderm
acoelomate, pseudocoelomate, eucoelomate
eucoelomate is the same as coelomate - triploblastic animal w coelom
origins of cnidaria: cnidaria-first vs comb-jelly first
cnidaria first: based on characteristic features and least number of evolutionary events (including losses of characteristics)
comb jelly first: comb jellies have more genes, they hv neurotransmitters, internal gut
overview of cnidaria phylogeny:
classical view = porifera first —> phylogeny still under development
what is the main difference in polyp and medusa stages ?
reproduction:
polyp = asexual
medusa = sexual (produce gametes)
hydrozoan features:
complex life cycles
presence of velum
gametes produced in epidermis vs endodermal tissue
hydrozoa morphological feature:
polymorphism:
colonial organisms that are genetically identical but perform different functions
polymorphic hydrozoan colony components and an organism example
gonozooid - reproductive polyp
gastrozooid - feeding polyp
dactylozoids - defense polyp
medusa - sexual stage
example : siphonophora - portuguese man of war
what are the main differences between hydrozoan and schyphozoan life cycle?
hydrozoan - can have polymorphic colony of diff polyp forms
schyphozoan - has strobila — releases ephyra (grows into medusa)
how does environmental change affect medusazoans vs anthozoans
- eutrophication
— medusazoan larva takes up all the nutrients, more larva produced
— anthozoans are overrun by algal growth on coral - global warming
— medusazoans supported by warmer temp
— anthozoans : warming breaks down symbionts, coral bleaching - overfishing
— medusazoans: overfishing reduces fish eating larvae
