Lecture 2 RH Flashcards
What are some examples of cnidarians?
Hydroids
Corals
Sea anemones
Sea jellies
etc
How are tissues different in cnidarians compared to phylum porifera?
More differentiation and formation of true tissues
What are the key features of phylum cnidaria?
True tissues
Diploblastic (2 germ layers; endoderm and ectoderm)
2 organised adult layers of tissue the epidermis and the gastrodermis with mesoglea between them.
radial symmetry
Blind gut (no anus)
Hydrostatic skeleton
Simple muscular and nervous systems
Have cnidocytes which capture prey
Carnivorous
All are aquatic and mostly marine
Why are cnidarians said to have true tissues?
Cells overlay a basal lamina which is a sheet of collagen
Gap junctions
Presence of an epithelium
What is the mesoglea?
Jelly-like layer between gastrodermis and epidermis
What kind of symmetry do cnidarians have?
Radial symmetry
Do cnidarians have a gut?
Yes a blind gut (entry and exit are both from the same place)
Do cnidarians have a skeleton?
Yes a skeleton that relies on water pressure to be effective
Do cnidarians have a muscular and nervous system?
Yes, a simple nervous and muscular system
How do cnidarians feed?
They capture prey with their cnidocytes.
*This means they are carnivorous
What happens during cleavage?
Blastula is formed which is a hollow sphere of cells (blastocoele is the space inside)
What happens during gastrulation?
Pouching in of cells to form blastopore and gastrocoele.
Outer layer is ectoderm and inner layer is endoderm
What are the subclasses of Metazoa?
Parazoa (no true tissues)
Eumetazoa: Can be either diploblastic or triploblastic
What are the three types of cells that are important for cnidarians to be carnivorous?
Myoepithelial cells (epithelium that can contract)
Nerve cells (Nerve nets)
Cnidocytes (unique to this phylum)
What is the function of myoepithelial cells?
Locomotion
What kind of muscles can be found in the epidermis?
Longitudinal muscle filaments
What kind of muscles can be found in the gastrodermis?
Circular muscle filaments
How do cnidarians sense environmental stimuli and respond?
No central nervous system so they directly react to environmental stimuli
What is the function of cnidocytes?
Subdues prey via its nematocysts which injects toxin into its prey.
What does the nematocyst do and what stimulates its function?
Nematocyst
How do nematocysts fire in response to physical stimulation?
Cnidocil is sensitive to touch. When it is stimulated it penetrates the skin of its prey and injects poison into it.
What are the body forms that cnidarians occupy?
2 body forms which occupy different stages of a cnidarian’s life cycle:
Polyps
Medusa
How is the class of cnidarian determined?
The predominance of the medusa stage or polyp stage determines which class it belongs to.
What develops from the gastrula stage?
Gastrovascular cavity (blind cavity due to no anus)
Does the gastrovascular cavity exist within the tentacles?
Yes
What does medusa dominance indicate about its life cycle?
Generally Pelagic
What does polyp indicate about its life cycle?
Generally benthic
What are the asymmetric sides of cnidarians called?
Oral side
Aboral side
What is the symmetry of cnidarians?
radial
How does the hydrostatic skeleton keep the cnidarian functioning?
Mouth contains a sphincter which maintains a hydrostatic pressure within the cnidarian’s body
How does the hydrostatic muscle work?
Body consists of circular muscle around it and longitudinal muscle. When longitudinal muscle contracts body becomes shorter and fatter and vice versa when circular muscle contracts
How are longitudinal and circular muscles related?
They are antagonistic
How do cnidarians reproduce asexually?
Budding (Body develops and outpocket which develops into another organism)
Fission (Separation occurs in the middle creating 2 individuals in a similar way to bacteria)
What does asexual reproduction often result in?
clonal aggregation (linked via gastrovascular cavity)
*Sea anemones do this
What is a polymorphism in a colony?
Some individuals specialize in doing a certain function while other individuals perform another function
What are some examples of specializations that the different individuals of a hydroid colony could perform are?
gastrozooid (contain tentacles and are important for feeding)
Gonozoid (responsible for reproduction)
Are cnidarians mono or dio ecious?
Dioecious (forms larvae)
What is the larva of a cnidarian called?
Planula larva (swimming gastrula)
What are the classes of phylum cnidaria?
Hydrozoa (greatest variation in life cycles)
Scyphozoa
Cubozoa
Anthozoa
Staurozoa
What are the distinguishing features of hydrozoa?
Nematocysts are only present in the epidermis, not the gastrodermis. (can’t sting within the body cavity)
Both polyp and medusa stages are important
What is meant when hydrozoans are said to have greatest variations in life cycle?
Some hydrozoans have dominant medusa stages whereas others have dominant polyp stage.
How do hydrozoans reproduce?
Polyp is found in colonies. Polyp buds off to form medusas that can reproduce sexually by releasing sperm and eggs to form planulas.
What is the manubrium of a hydromedusa?
An extension of the mouth (the neck)
What is the velum?
lip of tissue around the edge of a hydromedusa which is unique to it.
What are the features of the siphonophore class of hydrozoans?
drifting colonies of polyps/medussae and show many polymorphisms.
What are the structural components of the physalia (AKA portugese Man-O-War or Blue Bottle)?
Pneumatophore (a specialized polyp that serves as a float)
Gonozoids
Gastrozooids
Dactylozooids (They just sting)
What are the features of the velella velella?
One central gastrozooid that does all the feeding
Gonozooids
Dactylozooids
What is a unique feature of the physalia?
1 specialized polyp called the pneumatophore that functions as a float.
What is a unique feature of velella velella (By the wind sailor)?
They have a sail which makes them float over the water with tentacles following under.
They have a specialized polyp for feeding.
What do some siphonophores with specialized medusae use their medusae for? Name an example of this.
Specialized medusae propel the entire colony together while the polyps function to feed.
Erenna (also contain bioluminescent lures)
What are features of hydrocorals?
Polyps are colonial
Secrete calcarous exoskeleton, very similar to true coral
Nematocyst of fire coral produce burning sensation
Extremely toxic
Most common in Australia (Yay?)
What are features of Class Scyphozoa?
Medusae dominate the life cycle
Very large medussae (much larger than hydrozoan medussae)
Swim by jet propulsion
Sensory organs are called rhopalia allow them to orient themselves in response to stimuli
Describe the scyphozoan life cycle:
1) Males and Females spawn sperm and eggs and they fertilize and form a planula.
2) Planula then grows into a scyphistoma polyp which undergoes asexual reproduction forming many copies of itself.
3) The resultant polyps stack on top of each other like cups and form what is called a strobilation.
4) Strobilation then turn upside down and forms a medusa and is called an ephyra which becomes an adult medusa.
What are some structural features of scyphozoa?
Tentacles at the rim of the bell
Oral arm extensions of manubrium containing nematocysts
Much of the arm consists of mesoglea
gonad is contained within the bell (looks like a 4 leaf clover)
Rhopalia around the edge of the bell
How does the rhopalium provide sensory information of direction and
Contains a hard ball of calcium carbonate called a statolith. And its hanging down and as the bell tips it swings from one side to another and there is cilia on both sides which controls which direction the hairs face allowing the scyphozoan to detect the location of the surface relative to current position.
How do scyphozoans detect light?
Ocellus in rhopalium detects location of light
How does jet propulsion work?
Longitudinal muscle contract making the jellyfish wider and then the circular muscles contract forcing water outwards and in turn creating thrust.
What are the features of Class Cubozoa?
Medusa dominates life cycle
No strobiltion
Most toxic of all cnidarians
Contain eyes with a lens, cornea, and retina
What does the cubozoan lifecycle look like?
1) Sexually reproduces to form a planula.
2) Planula grows up to form a larval polyp (B scyphistoma)
3) Budding may produce more polyps
4) metamorphosis occurs to form a medusa that swims freely
What are features of anthozoans?
Sessile
No medusa stage at all
What is the anthozoan life cycle like?
Polyp spawns sperm and eggs which fertilize into planula and then polyp again.
What are some anatomical features of anthozoan polyps?
Sphincter runs around oral disk.
Pharynx leads to gastrovascular cavity
How does a sea anemone that has expelled all its water fill up with water again?
It draws water into gastrovascular cavity via the cilia to inflate itself again.
What are the septa within anthozoans for?
Flaps of tissue form complete and incomplete septa around the pharynx. The septa are open at the bottom of the pharynx at the gastrovascular cavity which allows a larger surface area.
These septa contain lots of nematocysts to sting inside.
What are acrorhagi?
Inflated individuals with lots of nematocysts found between colonies so that they can sting each other to destroy the competition. Ridge develops between them called “no man’s land”
What are stony corals?
Hard corals. scleractinian corals have a surrounding external skeleton of CaCO3 secreted from the epidermis of the base.
Polyp can retract into the base of CaCO3 during the day and then filter feed at night.
What are the features of subclass zoantharia?
subclass Zoantharia (hexocorallia) tentacles are always in multiples of 6.
Sea anemones and some corals are in this group.
Acrorhagi are typical of these groups (agressive tentacles)
Stony corals also belong to this group
What are the subclasses of anthozoans?
Subclass zoantharia (6 tentacles per set)
Subclass Octocorallia (8 tentacles with pinnules and an internal skeleton)
What are pinnules?
a secondary division of a pinnate leaf, especially of a fern.
What are features of subclass octocorallia?
8 tentacles per set
internal skeleton (collagen or CaCO3 surrounding an axial rod)
pinnules
contain spicules
One specialized inflated polyp supports the colony
Why are cnidarians bio-luminescent?
Many cnidarians bioluminesce in several different patterns due to symbiotic algae. (Sea pens luminesce when touched)
What are hermatypic corals?
Reef-building corals
What are some examples of hermatypic corals?
Hexacorals and Octocorals
How do hermatypic corals typically reproduce?
spawning of hermatypic corals are synchronized and gametes are released at the same time
What are zooxanthellaes?
endosymbiotic dinoflagellates
Where can zooxanthellaes be found?
All hermatypic corals
What do zooxanthellaes do?
Intracellular symbionts in gastrodermis.
Release photosynthate to coral; coral waste provides nutrients to the algae.
What is coral bleaching?
Happens when corals lose symbiotic algae due to environmental stress. This causes algae to migrate through gut wall and to leave through mouth.
What causes coral bleaching?
Environmental stressors such as:
Rising sea water temperature
Increased UV radiation
Elevated CO2
Reduced salinity
Pollution
Diseases
Result is loss of zooxanthellae. However symbionts can be replaced with other algae.
What is class staurozoa?
Newly recognized class
Life cycle similar to anthozoans
Solitary polyp with 8 tentacles each with a cluster of smaller tentacles at hip
What are cteophores?
Small phylum very similar to cnidarians but they don’t have cnidocytes.
No contractile bell but instead use cilia.
Use colloblasts to immobilise prey
