Lecture 2 DA Flashcards
Do Cnidarians have true tissue? What are some features of their tissue (2)?
They do. They have a basal lamina and cells have intracellular junctions.
What are the cell layers of jellyfish?
Outer epidermis, inner gastrodermis.
In between is the mesoglea, which isn’t organised, ans is jelly-like.
Is the mesoglea an organised tissue layer? Is it a true tissue layer?
No, so it isnt a true tissue layer.
What can be said of the gut of jellyfish?
It is a blind gut, as there is no anus.
What water environment do cnidarians mostly inhabit?
Mostly marine.
What is gastrulation?
Formation of cell layers.
Where does gastrulation occur?
In the blastula.
How does a blastula form a blastocoele?
During gastrulation, it invaginates to form a blastocoele in the middle, and is the endoderm. The outer layeris the ectoderm.
After a blastocoele formation, how can the two cell layers be drawn together?
The blastocoele in the middle can collapse to draw them together.
What is the mesoglea derived from embryonically? Is it a true tissue layer?
It is derived from ectoderm, and is between ecto and endoderm. It isnt a true tissue layer however as it isnt organised.
What is a diploblast and triploblast?
dplio-2 cell layers
triplo-3 cell layers
What is a parazoa?
Has no true tissue.
What is a eumetazoa?
Has true tissue.
What are myoepithelial cells? What is their purpose in cnidarians?
Epithelial cells with contractile function. Provides locomotion.
Where are myoepithelial cells found in cnidarians?
Below the epidermis, and above the gastrodermis.
Which direction do gastrodermal myoepithelial cells run?
Circularly.
Which direction do epidermal myoepithelial cells run?
Longitudinally.
Which direction do gastrodermal and epidermal myoepithelial cells run relative to each other?
90 degrees.
Functionally, what are the actions of the two myoepithelial cells relative to each other?
They are antagonistic.
Do cnidarians have a central nervous system?
No.
What is the nervous system of cnidarians like?
They have a nerve net instead, allows sensory information from the environment.
What does the nervous systme of cnidarians allow it to do?
Allows a response to stimuli, but cant direct actions well.
Where are cnidocytes found?
In the epidermis.
What other kinds of animals have cnidocytes besides cnidarians? What is this termed?
None, it is unique to cnidarians. It is a synanomorphy.
What is the function of cnidocytes?
Immobilise and capture prey.
What organelle do cnidocytes contain?
Cnida.
What is the most common cnida?
Nematocyst.
What triggers cnida?
Cnidocil.
How do cnidocytes function?
The trigger, the cnidocil, fires off, and a needle shoots out, and is loaded with toxins, or is hooked (or both).
What are the two forms of cnidarians?
Polyps and medusae.
What distinguishes the classes of cnidaria?
Predominance of the polyp or medusa form.
Are cnidarians stuck with one form for life?
They can be either form, but will pass each form in its lifecycle.
What is the gastrovascular cavity?
The mouth of both forms leads to the gastrovascular cavity.
What forms the gastrovascular cavity?
The gastrocoele, which enlarges.
What can be found around the mouth of cnidarians?
Ring of tentacles called cnidocytes.
Does the gastrovascular cavity extend into the tentacles/cnidocytes? Why/Why not?
Yes, the cavity allows diffusion of nutrients, and for the tentacles to be supplied, the cavity must extend into them.
If the gastrovascular cavity is a blind cavity, where do waste products go?
Spit back out through the mouth, something ogres tend to do often as well.
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What are the advantages of a complete gut versus a blind ending one?
Allows for specialised regions, ie, one for protein breakdown (stomach), one for nutrient absorption (intestine), one for storage (rectum) etc…
Also allows animals like the earthworm to move through the earth continuously.
Are polyps motile?
No, they are mostly sessile, some can cartwheel across the floor.
What is meant by benthic?
An organism that lives on the ocean floor.
Where do medusa live?
In the water column.
What is meant by pelagic?
They live in the water column and swim freely.
What are the two sides of medusae?
Oral side - has the mouth
Aboral side - top of the jelly-like thingy
What is the advantage of being radially symmetrical?
Allows it to respond to stimuli from all sides.
What are the two sides of polyps?
They have an oral disk and aboral disk (anchored to the floor).
What are the skeletal supports for the jellyfish (2)?
Pressurised fluid within the gastrovascular caivty.
Sphincter around the mouth allows pressurising.
What forms are hydras?
Always polyps, never medusa.
What forms of reproduction do hydras have (4)?
Both sexual and asexual, including budding and fission.
How do hydras bud?
Similar to yeast budding, it grows on the side and pinches off.
How do hyras split by fission?
Stretches out and splits in the middle.
Where do budding medusae grow?
In the gastrovascular cavity.
So sea anemones aggregate together? Are they connected?
Yes, they do, as clones. They are not connected.
How do sea anemone form coral?
When aggregated, rather than being split clones, they are still connected and share resources.
What is an advantage of forming a colony? What is this termed?
Allows individual anemones in the colony to specialise for certain functions. Termed polymorphism.
Are anemones diecious?
Yes
What happens to eggs once fertilised?
Form larva and swim to the sea floor and develop into either medusae or polyps.
What is a cnidarian larva called?
Plantula.
What happens when two different aggregations of coral come together?
They fight each other, and a line can be seen in between them.
What are the 5 classes of cnidarians?
Hydrozoa Scyphozoa Cubozoa Anthozoa Staurozoa
What is a distinguishing feature of hydrozoa?
Nematocyst isn’t found in the gastrovascular cavity, all other classes have them there.
Hydrozoa only have it on their epidermis.
What forms does the hydrozoa have?
Both polyp and medusa, has greatest variation in forms.
Some species have entirely one form, but generally equal.
What happens when a larva finds a suitable surface?
Anchors and forms a polyp, and begins budding.
What are gastrozoas?
Feeding tentacles.
What are gonozoas?
Bud off new medusae.
What are dactylozoas?
Defensive stinging tentacles.
What is the manubrium? Which form has it?
Extension of the mouth in medusae, is a throat like structure, hanging from the top of the bell.
All medusae have it.
What is one structure that hydrozoan medusae have that others dont?
Ring around the mouth called velum. If a velum is present, its a hydrozoa medusa.
What form are hydras?
Entirely polyp.
What form are hydromedusae?
Entirely medusae.
What form is the obelis?
Goes through both.
What relation does the obelis have with hermit crabs?
Can be symbiotic.
What is a siphonophore?
Order within hydrozoa, drifting colonies of polyps, medusae or both.
What is a pmneumatophore?
Specialised polyp found in the man o’ war jellyfish. Specialised for floating.
How does the man o’ war feed?
Via one central gastrozoa.
What are hydrocorals? What do they secrete?
Polyps that are colonial. Secrete calcareous exoskeleton.
What class is the most diverse?
Hydra.
What form dominates the schyphozoa? Are they true jellyfish?
Medusa, polyp form is short-lived. Are true jellyfish.
What is a schyphozoa larva called?
Schyphistoma.
What is strobilation? Which class is it found in?
Asexual reproduction, where it buds off many copies of itself. Can be found in Schyphozoa.
What are juvenile medusae in strobilation called?
Ephyra.
Where is the rhopalia, and what can be found there?
Rhopalia is found at the edge of the bell. Contains sensory organs.
Where are the gonads found?
Gastrovascular cavity.
What does the manubrium do?
Extends downward to form oral arms to aid in prey capture.
What is a statocyst, and what is its purpose.
Found at the rhopalia, it has a hanging ball of CaCO3. Detects balance, allowing orienting.
What is the hanging ball of CaCO3 in statocysts called?
Statolith.
What is the ocellus?
Detects light, allows it to orient relative to light.
Relative to water intake/expulsion, what do circular myoepithelial cells do? What about longitudinal?
Circular - expels water
Longitudinal - draws water
What form dominates cubozoa?
Medusa.
What class is the most toxic of all cnidarians?
Cubozoa.
Do jellyfish have eyes?
Yes, cubozoa have lens and a cornea.
What are cubozoa larva called?
Scyphistoma.
How many subclasses do anthozoa have, and what form dominates them?
3 subclasses
No medusa stage at all
Are anthozoa diecious?
Yes.
Do anthozoa have sphincters?
Yes, an oral one.
In anthozoa, what can be found just deep to their oral sphincter?
A pharynx, which leads to the gastrovascular cavity.
What can be found on the pharynx? What purpose does it have?
Cilia called siphonoglyphs. Used to draw water in, allowing it to inflate itself.
What are folds in the gastrovascular cavity called (anthozoa)? Are they complete or partial folds?
Septa.
Has both complete and incomplete.
Complete extend all the way tot he edge of the body.
What is the purose of folding in the gastrovascular cavity?
Higher surface area, also allows it to sting more, as its covered in cnidocytes.
What are zoantharia/hexacorallia, and how many tentacles do they have?
Subclass of anthozoa, and have tentacles in multiples of 6.
What are acrorhagi (anthozoa)?
Aggresive tentacles that inflate to attack only.
What are scleractinian/stone corals like?
Polyp wits on top of an external skeleton, in depressions called sclerosepta. Can retract into them during daylight, extend at night.
What are octocorallia? How many tantacles do they have?
Soft corals, subclass of anthozoa. Always have 8 tentacles.
What can be found on octocorallia tentacles?
Pinnules.
What kind of skeleton does an octocorallia have? What is its structure
Internal skeleton, isnt hard, made of collagen, but can be reinforced by CaCO3 or spicules.
Where is the skeleton of octocorallia found?
In the mesoglea.
True or false
Octocorallia cant bioluminesce
False.
What kind of coral are octocorallia (besides soft)?
Hermatypic - reef building.
How are reefs built?
CaCO3 secreted, which builds up.
What relationship do coral have with algae? What kind of algae is it?
Endosymbiotic, they live in the gastrodermis.
A type of dinoflagellate.
Where does 90% of the coral nutrition come from?
The algae, via photosynthesis products.
How do corals get their colour?
From algae.
How is the nitrogen waste of corals beneficial?
The algae can use them.
What happens in coral bleaching?
Symbiosis lost.
What are some causes of coral bleaching (6)?
- Rising sea temperatures
- Increased UV radiation
- Elevated CO2 levels - acidifies the water
- Reduced salinity
- Pollution
- Diseases
What happens in coral bleaching exactly?
Algae migrate out of the gastrodermis, and expelled through the mouth, hence the term bleached, as colour is lost.
Are the algae actively expelled by the coral?
Yes.
Does the algae population is a given coral change?
Yes, the coral actively manages its algae population annually.
Old senescent algae are expelled so they can pick up healthier ones.
What is the hypothesis behind why algae are expelled in coral bleaching?
They are expelled by the coral because the algae are stressed, so they can pick up new symbiotes, selectively that are better.
If coral actively expel their algae to pick up healthier ones, why do they still get bleached?
Most of the algae are expelled, and 90% of their nutrition comes from them, so they die quickly due to malnutrition.
What can be said of the class staurozoa planula?
It doesnt swim.
What are the tentacles of staurozoa like?
Their tentacles also have tentacles on them, and looks like a star.
What form are staurozoa?
Exclusively polyp.
What is another phylum that exhibits radial symmetry?
Ctenophore.
Do ctenophores have nematocysts?
No.
What are ctenes?
Ciliated combs found on ctenophores.
What water environment do ctenophores live in?
Entirely marine.
