Transcript Chapter 8 Phylum Cnidaria

Lecture Exam I
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Cambrian radiation / phylogeny = 2 papers
Systematics intro
Protista: 10 phyla
Animalia: Porifera, Cnidaria
• ~20 questions
• Short answer, essay, life cycle sketch
Phylum Cnidaria
• 3 Classes:
– Anthozoa
– Scyphozoa
– Hydrozoa
Characteristics:
• Diploblastic metazoan
• Ectoderm and endoderm separated by acellular
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mesoglea
Nervous system: simple nerve net, neurons
Development
• Planula larvae
• ciliated, motile, gastrula larva
Radial symmetry
• Modified into
biradial, quadradial,
etc…
Gastrovascular cavity
• Saclike, partitioned, or branched w/ one opening
• = mouth and anus
Alternating life history forms:
polyp and medusa
Polyp
• Radial symmetry
• Oral end = hypostome or manubrium in
hydrozoans
– flat pedal disc in anthozoans
• Tentacles surround mouth
Polyp
Gastrovascular cavity
• Circulation, digestion, distribution of nutrients
• Hydrozoans: coelenteron is single tube
• Scyphozoans: four longitudinal mesenteries
• Anthozoans: compartmentalized by
mesenteries
Polyp: support
• Hydrostatic, water-filled coelenteron
• Anthozoans - bits of sediment and shell fragments in
column wall for support
• Hydrozoans - flexible horny perisac (periderm) of chitin
from epidermis
Polyp: movement
• Retractor muscles: longitudinal fibers along
mesenteries
• Circular muscles: sphincters
– in tentacles and oral disc
• Most polyps sedentary or sessile
• Creep slowly w/ pedal disc musculature
• http://www.youtube.com/watch?v=UI531GMRTM
Medusa
• All cnidaria except Anthozoa
• Bell-, dish- or umbrella-shaped
• Exumbrella: convex upper (aboral) surface
• Subumbrella: concave lower (oral) surface
– Mouth at center
Free-floating,
mouth down
Medusa
• External surface: epidermis
• Internal surface: gastrodermis
• Coelenteron central; extends to radial
canals
– Usually four radial canals, tentacles,
stomach divided by mesenteries into
four gastric pouches
Nematocysts
• Stinging structures
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Nematocysts: multiple types
• Generic nematocyst (all)
– Double-walled capsule w/ toxic mixture of phenols + proteins
– Spines or barbs for penetration, anchor in victim
• Spirocyst (Anthozoa)
– Spring-like mechanism
– Adhesive tubules wrap around and stick to victim
• Ptychocyst (tube anemones)
– Create capsule tubule
Feeding and digestion
Tentacles capture prey, carry to mouth, ingest whole
Extracellular digestion in coelenteron
– enzyme-producing cells
Reproduction and Development
Hydrozoa
• Polyps = asexual budding
Reproduction and Development
Hydrozoan
• Free-living hydromedusa
• Dioecious, release sperm or eggs
Reproduction and Development
Scyphozoa
• Asexual reproduction: small polyp =
scyphistoma
• Medusa from scyphistoma
• Immature medusa = ephyra
• Most species dioecious
Reproduction and Development
Anthozoa
• Exclusively polyps
• Asexual reproduction
• Fission
• Pedal laceration: pedal disc spreads,
anemone moves, leaves small fragments
– develop into adult
Class Hydrozoa
Hydroids and hydromedusa
Hydrozoa
Portuguese Man-of-war
Physalia
Class Anthozoa
Anemones, corals, sea pens
Exclusively marine
Octocorals
• Soft corals
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Gastraxonacea
Helioporaceans
Sea pens and sea pansies
Protoalcyonaria
Stoloniferans
Telestaceans
Sea pen
Class Anthozoa
Anemones and true corals
• True sea anemones
• True corals (stony corals)
Class Anthozoa
• Black or thorny corals
• Ceranthids or tube anemones
Class Scyphozoa
• Jellyfish
Box jelly
Chiropsalmus