Cnidaria Flashcards
Cnidarian bodies consist of _____, a non-living jelly-like substance, sandwiched between ____ layers of epithelium that are mostly ____ cell thick
mesoglea, two, one
Many cnidarian species produce ______ that are single organisms composed of ____-like or ____-like zooids or both.
colonies, medusa or polyp
How are cnidarian activities coordinated?
A decentralized nerve net and simple receptors, some have simple eyes.
What are the major taxa of cnidaria?
Anthozoa (class): Corals, anemones, sea pens
Medusozoa (subphylum): Jellyfish, hydroids
Myxozoa (subphylum): Myxozoan parasites
The oldest estimate for the arrival of cnidarians, derived from molecular clock methods is _____
791 million years ago, before the Cambrian explosion
In what ways are Cnidarians more complex than sponges?
Cells bound by inter-cell connections and carpet-like basement membranes; muscles; nervous systems; and some have sensory organs
How are cnidarians distinguished from all other animals?
Cnidarians are distinguished from all other animals by having cnidocytes that fire like harpoons and are used mainly to capture prey. In some species, cnidocytes can also be used as anchors
How do medusae swim?
Medusae swim by a form of jet propulsion: muscles, especially inside the rim of the bell, squeeze water out of the cavity inside the bell, and the springiness of the mesoglea powers the recovery stroke. Since the tissue layers are very thin, they provide too little power to swim against currents and just enough to control movement within currents
Describe the skeletons of the different groups of Cnidaria
Medusae: mesoglea.
Hydra and most sea anemones: close their mouths when they are not feeding, and the water in the digestive cavity then acts as a hydrostatic skeleton, rather like a water-filled balloon.
Tubularia: columns of water-filled cells for support.
Sea pens stiffen the mesoglea with calcium carbonate spicules and tough fibrous proteins, like sponges.
In some colonial polyps, a chitinous periderm gives support and some protection to the connecting sections and to the lower parts of individual polyps.
Stony corals secrete massive calcium carbonate exoskeletons.
Describe the nervous system of Cnidaria
They have integrative areas of neural tissue that could be considered some form of centralization. Most of their bodies are innervated by decentralized nerve nets that control their swimming musculature and connect with sensory structures, though each clade has slightly different structures
Siphonophores and chondrophores sense tilt and acceleration by means of _______, chambers lined with hairs which detect the movements of internal mineral grains called statoliths
statocysts
What are ocelli?
Simple eyes that can detect sources of light.
What are cnidarian feeding mechanisms?
Predation, absorbing dissolved organic chemicals, filtering food particles out of the water, obtaining nutrients from symbiotic algae within their cells, and parasitism.
What do cnidaria give their endosymbionts?
Carbon dioxide, some nutrients, a place in the sun and protection against predators.
Digestion is ____ cellular
Intra- and extra-
Describe Cnidarian excretion
Indigestible remains of prey are expelled through the mouth. The main waste product of cells’ internal processes is ammonia, which is removed by the external and internal water currents.
Describe Cnidarian digestion
Once the food is in the digestive cavity, gland cells in the gastroderm release enzymes that reduce the prey to slurry, usually within a few hours. This circulates through the digestive cavity and, in colonial cnidarians, through the connecting tunnels, so that gastroderm cells can absorb the nutrients. Absorption may take a few hours, and digestion within the cells may take a few days. The circulation of nutrients is driven by water currents produced by cilia in the gastroderm or by muscular movements or both, so that nutrients reach all parts of the digestive cavity.[10] Nutrients reach the outer cell layer by diffusion or, for animals or zooids such as medusae which have thick mesogleas, are transported by mobile cells in the mesoglea.[9]
Describe Cnidarian respiration
There are no respiratory organs, and both cell layers absorb oxygen from and expel carbon dioxide into the surrounding water. When the water in the digestive cavity becomes stale it must be replaced, and nutrients that have not been absorbed will be expelled with it. Some Anthozoa have ciliated grooves on their tentacles, allowing them to pump water out of and into the digestive cavity without opening the mouth. This improves respiration after feeding and allows these animals, which use the cavity as a hydrostatic skeleton, to control the water pressure in the cavity without expelling undigested food.[9]
Cnidaria that carry photosynthetic symbionts may have the opposite problem, an excess of oxygen, which may prove toxic. The animals produce large quantities of antioxidants to neutralize the excess oxygen.[9]
Describe cnidarian regeneration
All cnidarians can regenerate, allowing them to recover from injury and to reproduce asexually. Medusae have limited ability to regenerate, but polyps can do so from small pieces or even collections of separated cells. This enables corals to recover even after apparently being destroyed by predators
Describe the cnidarian complex life cycle
Cnidarian sexual reproduction often involves a complex life cycle with both polyp and medusa stages. For example, in Scyphozoa (jellyfish) and Cubozoa (box jellies) a larva swims until it finds a good site, and then becomes a polyp. This grows normally but then absorbs its tentacles and splits horizontally into a series of disks that become juvenile medusae, a process called strobilation. The juveniles swim off and slowly grow to maturity, while the polyp re-grows and may continue strobilating periodically. The adults have gonads in the gastroderm, and these release ova and sperm into the water in the breeding season.[9][10]
This phenomenon of succession of differently organized generations (one asexually reproducing, sessile polyp, followed by a free-swimming medusa or a sessile polyp that reproduces sexually)[24] is sometimes called “alternation of asexual and sexual phases” or “metagenesis”, but should not be confused with the alternation of generations as found in plants
What preys on cnidaria?
Sea slugs, which can incorporate nematocysts into their own bodies for self-defense;[38] starfish, notably the crown of thorns starfish, which can devastate corals;[34] butterfly fish and parrot fish, which eat corals;[39] and marine turtles, which eat jellyfish
What is the different between ahermatypic and hermatypic corals?
Whether they are reef-building or not.
What is the name of the sac-like central body cavity in porifera and cnidaria?
Coelenteron
What are mechanisms of cloning in corals?
a. Fragmentation via mechanical breakage
(e.g. storms, bioerosion, partial predation, … )
b. Fragmentation via dieback of coenosarc (tissues)
and coenosteum(skeleton)
b. Polyp balls (e.g. Goniopora stokesi)
c. Polyp “bailout” Mass detachment of polyps ( plankton)
d. Single polyp detach and walk away ( as “anemones”)
e. Asexual larvae (no meiosis)
(= “true” asexual reproduction
Describe heterotrophic coral feeding
• Nematocysts capture prey or particles • Tentacles capture food & push into coelenteron for: – Extracellular digestion – Phagocytosis – Intracellular digestion • Mesenteries and filaments for digestion
What are some other heterotrophic feeding strategies?
- Mucus strands – “fishing”
- Mucus sheets – particulate feeding
- Mucus sheets ‐ microbial “culture”
- Dissolved organic molecules
- Mesenteric filaments ‐ detritivores
What are the advantages of photosynthetic endosymbionts?
Major energy source for corals, increases calcification rate.
What are the advantages of photosynthetic endosymbionts?
Major energy source for corals, increases calcification rate.
• Zoox get CO2 & nutrients from coral • up to ~95% of sugars to corals • up to ~98% of coral’s energy (triglycerides cetyl palmitate) • accelerate coral growth • increase calcification (5–20 X) • enable dominant reef‐builders
What marine organisms have photosynthetic endosymbionts?
Clams, anemones, corals, etc.
When did photosynthetic symbionts arise in corals?
Around Triassic, 220 mya.
What are the major clades of coral symbionts and their environmental preferences?
– Types A and B –tolerant of high light
– Type C – shade loving
– Type E – relatively common on nearshore reefs
How do corals get zooxanthellae?
Vertical transmission
= zooxanthellae in egg or brooded larvae
• Horizontal transmission
= gained from seawater when feeding (via phagocytosis)
What is phagocytosis?
In cell biology, phagocytosis is the process by which a cell—often a phagocyte or a protist—engulfs a solid particle to form an internal compartment known as a phagosom
What is the adaptive bleaching hypothesis?
May switch genetic type in severe environmental stress
What are the benefits for zooxanthellae of the symbiosis?
- Supply of N (from coral’s heterotrophy)
- Fixed position in water column and favorable light regime
- Protection from planktonic grazers
- CO2 from coral respiration
- CO2 from water
- Protection from UV
What are the specific benefits for the host coral?
- Photosynthate (carbohydrates & lipid precursors)
- Energy reserves (cetyl palmitate = wax ester)
- N recycling and conservation
- (?) O2 for metabolism
- Enhanced growth
- Enhanced calcification
Describe broadcast spawning.
- Gametes shed into water
- Fertilization external
- Zygote develops in plankton
Sperm can detect & move to egg in water • Development fast (48‐72 hr) • Long‐lived larvae (>100 days) (can settle ~ 2 day ‐ >3 mon) • Wide dispersal potential (Settle locally or far away) • Common all sexuality modes
Describe brooder spawning.
- Fertilization internal
- Zygote develops in coelenteron
- Mature larva released
Release only sperm to water • Retain eggs in coelenteron or mesentery • Internal fertilization • Brood larvae for <4 weeks to >15 months • Larvae “competent” to settle immediately • Both hermatypic and ahermatypic • Both zooxanthellate and azooxanthellate • Both solitary and colonial • Often have vertical transmission of zooxanthellae (mother to larvae) • Local and long‐distance dispersal • Some brood asexual larvae • Is self‐fertilization possible?
Describe sexual reproduction in corals.
Gametogenesis
• Many corals are gonochoric (separate sexes)
• Most corals are hermaphroditic (both sexes)
Development of zygote planula larva
• May be internal (brooding)
• May be external (planktonic)
• All larvae potentially have planktonic phase
Settlement and metamorphosis
• Many corals need coralline algae or bacterial film
Some corals have both sexual and asexual larvae
