7. Eumetazoa Intro: Cnidaria Flashcards
The clade Eumetazoa is characterized by phyla with ‘true tissues’, which are clearly derived from what?
embryonic ectoderm and endoderm layers
If ctenophora is more basal than placozoa and/or porifera, what’s implied about the evolution of true tissues?
either true tissues evolved more than once OR true tissues evolved once at the base of the metazoa (& were lost in porifera and placozoa)
T/F
Where ctenophores belong in the tree of metazoa is extremely contentious
true
we’ll stick to brusca 3rd ed: origin of ctenophora after porifera and placozoa
T/F
Eumetazoa= a POTENTIALLY real clade, united by the presence of true tissues derived from embryonic germ layers, and Brusca’s features 7-12 (synapomorphies)
true
potentially real, depending on where ctenophora truly belongs
List the 6 features Brusca et al. have identified as synapomorphies of Eumetazoa
- gap junctions
- gonads
- synaptic nervous system
- epithelium-lined gut
- primary larva
- presence of particular opsins
gap junctions=
a particular type of intercellular junction
- protein tubes that allow dissolved substances to pass from one cell to the next without having to go through cell membranes
- synapomorphy of eumetazoa
The synaptic nervous system of eumetazoa is derived from ___ ____.
What does ‘synaptic’ refer to?
embryonic ectoderm
the arrangement of cells that permits a neuron to pass an electrical or chemical signal to another neuron or to some other target cell
The epithelium-lined gut of eumetazoa has ____ enzymes, and is derived from the embryonic ______
- synapomorphy of eumetazoa
digestive
endoderm
In eumetazoa,
- synaptic nervous system is derived from _________
- epithelium-lined gut is derived from ______
ectoderm –> nervous system
endoderm –> gut
The primary larva is a synapomorphy of eumetazoa. Describe what it is.
= a ciliated larva bearing a sensory apical organ (called a primary larva)
The presence of particular opsins are a synapomorphy of eumetazoa. Describe what opsins are
= proteins that bind to light-reactive chemicals
associated with vision, phototaxis, etc
Phylum Cnidaria includes ~____ extant species and many fossil ones (mainly corals)
13,300
T/F
Species in phylum cnidaria are mostly freshwater
false
mostly marine, with ~100 freshwater spp and no terrestrial spp
List the 3 subphyla of phylum cnidaria
- Anthozoa
- Medusozoa
- Endocnidozoa
How many class(es) are in subphylum Anthozoa? Give 2 examples of Anthozoans
1 class
corals, sea anemones
How many classes are in subphylum Medusozoa?
Give an example of a medusozoa
4
true jellyfish
How many classes are in subphylum Endocnidozoa?
These are morphologically ____. Are they symbionts or parasites?
2
reduced
completely parasitic
Cnidaria have 2 main body forms. Give & describe them
Polyps: benthic (lives on the bottom of the water body)
- asexual reproduction
Medusa: pelagic (swims in open water)
- sexual reproduction
- many spp alternate b/w the 2 forms, some have only 1 form in their life cycles
T/F
Free-living cnidarians often do not show clear polyp or medusa forms
false
In free-living spp, there are 2 main body forms (medusa and polyp)
PARASITIC cnidarians often do not show clear polyp or medusa forms
What is the primary body axis of free-living cnidarians?
oral to aboral
What symmetry to most free-living cnidarians have?
they’re roughly radially symmetrical
- rarely perfect
- often have 4-, 6-, or 8- fold radial symmetry
How many openings does the gut of most free-living cnidarians have?
1 opening
- mouth only, no anus
Cnidarians have tentacles, but they’re not just a cnidarian feature; many invertebrate taxa have tentacles.
Give the general definition of a tentacle.
What do cnidarians use them for?
tentacle= a general term for a long, thin, flexible appendage that is often sticky
Cnidarians use tentacles to capture prey & move food to their mouth
T/F
Cnidarians do not have specialized gas-exchange, excretory, or circulatory systems
true!
these roles are performed by the gastrovascular cavity
T/F
Cnidarian’s tentacles surround the aboral end, and are always hollow
false
surround oral end
can be solid or hollow
The gastric cavity of cnidarians may have water-filled branches or canals that go into different parts of the body.
What is this called?
Gastrovascular cavity
Do cnidarians exhibit a true tissue level of organization? Define
Yes!
= groups of differentiated cells that work together for a shared function
Are cnidaria diploblastic or triploblastic?
diploblastic
Give and describe the 2 true tissues layers in cnidaria
epidermis: outer layer, from ectoderm
gastrodermis: inner layer of tissue, from endoderm
these 2 tissue layers are true epithelial tissues with basal lamina
T/F
The mesoglea is a true tissue in cnidaria
false
The mesoglea (the middle layer) is mostly non-cellular and not a true tissue
Give the 2 most common types of cnidarian organs
gonads
light sensing structures
A synapomorphy of cnidarians is the unique and complex cell type called a cnidocyte.
Describe what a cnidocyte is
Cnidocyte= derived from gastrodermal interstitial cells and bear 1-2 fancy organelles:
- Cnida= capsule with sticky tube that may contain toxins
- Cnidocil (only in medusozoa)= cilium that acts as trigger & shoots out cnida if it’s touched
What is the most complex intracellular structure of all metazoa?
Cnidae!
nematocysts=
a type of cnidae
- has spines and toxins
- found in all free-living cnidarian taxa
T/F
Only 1 type of cnidae can occur in a single individual
false
1 or many types
Myoepithelial cells have ___ myofibrils.
What are the 2 functions of myoepithelial cells?
basal
- skin and ‘muscle’
Myoepithelial cells have basal myofibrils: how are these arranged in the
a) epidermis
b) gastrodermis
myofibrils are arranged longitudinally in the epidermis and circularly in the gastrodermis
In cnidaria, muscular contraction can act against the gastrovascular cavity as a ______ skeleton
hydrostatic
Describe how the nerve cells are organized in cnidaria
they form a loosely organized net (rather than a centralized nervous system)
Do cnidaria have a brain? Ganglia?
No and no
- the nerve cells form a loosely organized net
In most cnidarians, how are the nerve nets arranged?
In 2 arrays:
- epidermal one
- gastrodermal one
these are separated by the mesoglea
Planula larvae=
a free-swimming, flattened, ciliated, bilaterally symmetrical larva common to almost all groups of cnidaria
How do planula larvae develop?
- in scyphozoans and some hydrozoans
- in anthozoans
In scyphozoans and some hydrozoans, planula larvae develop from the fertilized egg of a medusa
In anthozoans: from the fertilized egg of a polyp
Planulae of the medusozoa have no mouth or digestive tract and do not eat. How do they get nutrients?
they’re lecithotrophic= get nutrients from egg yolk
How do the planulae of anthozoa get nutrients?
Some are lecithotrophic, while others can feed by eating smaller organisms (plankotrophy)
feeding by a planktonic larvae is called _______
planktotrophy
In most cnidarian taxa, what do the planula larvae do?
swims until it reaches an appropriate substrate where it settles and transforms into a polyp
In many open-ocean scyphozoans, what do the planula larvae do?
metamorphoses directly into a free-swimming miniature version of the adult
Which organism is usually used to illustrate the ‘classic’ alternation b/w medusa and polyp life cycles?
the hydrozoan obelia
T/F
Hydrozoa Aglaura lacks a polyp form
true
Does Tubularia (Hydrozoa) have a free medusa?
yes!
Both Tubularia and Aglaura have a planula and a tentacled ____ larva
actinula
T/F
The freshwater hydrozoan Hydra has both a medusa stage and a planula larva
false
opposite is true: Hydra LACKS both a medusa stage and a planula larva
T/F
Aurelia has both polyp and medusa stages
true
What is a scypistoma?
the polyp of Aurelia (Medusozoa, class scyphozoa) that can bud off more polyps or ephyra
What is an ephyra?
Juvenile medusae of Aurelia
- budded off the scyphistoma
Some scyphozoans, like _______ don’t have polyp stages
Pelagia
(b/c no benthic areas for it to settle)
All anthozoans lack a _______ stage
medusa
The Endocnidozoa “Myxobolus cerebralis” is parasitic and relevant to alberta. Does it have a polyp stage? Medusa?
No polyp or medusa!
Give the 4 synapomorphies for Cnidaria as a whole:
- polyp stage
- cnidae
- myoepithelial cells
- planula larva
T/F
Each of the 4 synapomorphies of cnidaria has been lost in some derived taxa
true
Molecular data supports a “polyp-first” hypothesis; this places _____ as the basal group
Anthozoans
