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5. Cnidaria II - Phylum Cnidaria Phylum Cnidaria corals...

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Unformatted text preview: Phylum Cnidaria Phylum Cnidaria corals, jellyfish, anemones, hydrozoans All aquatic ~ 11,000 living species (~ 5000 fossil sp.) CLASS ANTHOZOA Exclusively polypoid May or may not have skeleton – external CaCO3 or internal fused spicules Coelenteron compartmentalized by SEPTA (=MESENTERIES) septa have gonads, nematocytes ACONTIA – batteries of nematocysts Primarily Marine BIRADIAL symmetry Solitary or Colonial GASTROVASCULAR CAVITY Gonads – endodermal Ectoderm ! = STOMODEUM – considered derived SIPHONOGLYPH – ciliated groove mouth to G.V. cavity for water circulation Tentacles are Hollow 6-8 tentacles basic (or multiples of that) Simple nerve net Well dev. retractor muscle bundles Tissue Grade Diploblastic External skeleton covered by two thin layers of tissue May have skeleton of loose spicules May spicules Internal, e.g., soft corals, gorgonians Internal, Major Taxa to know: Taxa OCTOCORALLIA = ALCYONARIA ALCYONARIA 8 pinnate tentacles 8 septa mostly colonial Gorgonians, Organpipe coral, soft coral, sea pens, sea pansies Gorgonians, Organpipe Spicules can Spicules protect from predators, or give structural support support 1 ZOANTHARIA >8 tentacles (12 or cycles of 12 common) tentacles NOT pinnate solitary or colonial ACTINARIA anemones No skeleton usually 2 siphonoglyphs usually siphonoglyphs Class HYDROZOA Polyps easy to recognize – usually encased in exoskeleton – chitin or CaCO3 Medusae – have velum have a nerve ring around the bell Some: entirely medusoid dominant medusoid w/ reduced benthic polyp dominant budding off reduced medusa solely polyp form Why? SCLERACTINIA corals Mostly colonial heavy CaCO3 external skeleton heavy CaCO3 septa hexamerous septa hexamerous LIFE CYCLES Metagenesis – heteromorphic life histories Major diff among classes – relative time of benthic and pelagic phases. Within Hydrozoa – see full range of life histories NEOTENY – larval (juv) form develops sexual maturity ! truncation of life cycle PAEDOMORPHOSIS – ancestral adding on progessively to descendents life cycle. ! “ontogeny recapitulates phylogeny”? Some suggest that cnidarian life cycle differences are a heterochronic sequence Full life cycle would have both benthic (polyp) and planktonic (medusa) phases - reductions or expansion if different phases. Hydrozoans show full range of life cycles. Reflected in different classes. HETEROCHRONY – change in the timing (rate) of a life cycle (developmental phase) Are life cycles a heterochronic sequence? Hyrozoans Depends on who came first: Polyp or Medusa Planula or Actinula Maturation of polyp phase neoteny? Actinula derived from planula and becomes polyp – future reduction in medusa? Hydra – very reduced life cycle – very simple compared to marine counterparts. Among Classes? ?Scyphozoans Ancestral, Hydrozoans transitional, and Anthozoans derived? Evidence for this? How could we test these hypotheses??? Reproduction - Sexual and Asexual Variety of ASEXUAL modes - no gametes - budding - genetically identical products = CLONES common in Anthozoa & Hydrozoa Examples: Hydra – budding fission – Anthozoans pedal laceration – Anthozoans strobilation - Scyphozoans 2 Why Clone? Fission - energetic savings Fission occupy space group capture of larger food Acrorhagi Acrorhagi Outgrowths of the Outgrowths body packed with stinging nematocysts Only used for combat, not for feeding Anthopleura elegantissima SEXUAL modes – hermaphroditic (both male and female) dioecious (separate sexes) external or internal fertilization larvae released or brooded most larval stages non-feeding Many invertebrate life cycles – PELAGO-BENTHIC - pelagic larva / benthic adult aids in dipersal? take advantage of diff habitats? Think about this? Non-clonemates fight Lizbeth Francis 1988. Cloning and Aggression among Sea Anemones (Coelenterata: Actiniaria) of the Rocky Shore. Biol. Bull. 174:241-253. Similar things found in a wide range of anemones that clone. Tubularia have in lab produce actinula larva that settles produce actinula larva into a polyp. into Polyp only life history Predator - Flabellina - snail (sea slug) Predator sequesters the nematocysts of sequesters its prey in its cerrata - protection cerrata from its own predators Lots of examples in lab - look at the diversity of types and Lots life histories 3 FEEDING importance of architecture - e.g., colonial vs solitary importance e.g., vs Nematocysts and Cnidae – Read about structure, type & function in text Nematocysts Cnidae Look at these in the lab Solitary polyps Solitary large coelenteron, lots of surface area w/ septa large coelenteron lots capture large food, or small " ciliary mucus feeding Colonial – resources shared among units Colonial small food – shared & dist. through common gastrovascular system small shared gastrovascular large food – coordinated effort in capture and digestion large coordinated e.g. Physalia a SIPHONOPHORE, colonial hydrozoan Physalia SIPHONOPHORE colonial hydrozoan can be highly integrated – e.g. gorgonians can microcarnivores endodermal canals all polyps the same – no specialization all Specialization of polyps – Specialization e.g., Hydroids – Hydractinia e.g., gastrozoids ! feeding dactylozoids ! defense tentaculozoids ! sensory, defense spiralzoids – sensory gonozoids – reproduction Siphonophore colony (Hydrozoans) extreme example of colony coordination up to 4 polypoids & 4 medusoid forms/colony medusoid morphs (produced by gonozoids) nectophores – swimmers lack manubrium lack tentacles have umbrella phyllozoids – leaf like medusae – lots of cnidocytes, surround colony oleocytes – oil floats gonophores – bear gonads Mackie (1986) – Resource Sharing in siphorophores - observed movement of carmine lab food Colony develops by differentiation of clonal buds as they buds grow grow 4 Velella velella velella LOCOMOTION contrast jellyfish w/ siphonophores Jellyfish Daniel, T.L. mechanics and energetics of medusan jet propulsion. Can. J. Zool. 61:1406 – 1420 swim by jet propulsion ! rhythmically contracting bell margin. bell simple shape ! tractable system for analysis Siphonophores Bell contracted !contraction of muscles around velum – but no muscles opposite these – How does it reinflate? Elastic energy stored in bell – mesoglea acts like a rubber band Cost of transport by jet prop. very high – higher than any other form of locomotion feed at same time as move – offsets costs Coordination of this? medusae have a more organized nervous system and complex sensory structures than polyps Hydromedusae – nerve ring next to velum, innervates tentacles, ocelli, sensory tract, sensory epitheium, balance organs, muscles of velum & subumbrella Scyphomedusae – lack nerve ring, have ganglia associated with rhopalium (sensory structures) Mackie, G.O and D. Carre. Coordination in a diphysid siphonophore. Mar. Beh. Phys. 9:139-170 Mackie, G.O. 1986. From aggregates to integrates: physiological aspects of modularity in colonial animals. Phil. Trans. R. Soc. Lond. B 313:175-196 2 Modes of Swimming Normal – nectophores pulsate at natural freq. ! gliding vertical migration (can !" 400m in 24 hr) Escape – high velocity (20-30cm/sec) all nectophores contract in unison produced by different physiological pathways siphonophores have both a stem and nectophores (like medusa) stem coordinates giant axon (conducts impulses @ 1-3m/s) giant axon ! nervous trigger for escape response epithelial conduction – Normal swimming Siphonophores – colonial locomotion example – Nanomia Mackie, G.O. 1978 Coordination in physonectid siphonophores Mar. Behav. Physiol. 5:325 – 346 5 Phylum Ctenophora = comb jellies Phylum Ctenophora - marine - biradial symmetry - tissue grade - no polymorphism - not colonial - no sessile stage - muscle cells - Colloblasts – sticky cells - Ctenes = combs – 8 vertical rows of plates (Fused Cilia) combs - one way gut – mouth, anus one - hermaphrodite ! Cydippid larva hermaphrodite Beroe PREDATOR of Mnemiopsis Beroe Mnemiopsis Ctene rows coordinated - produce strong directional rows produce swimming swimming See your text for good illustrations of See how ctenes work and how they are organized ctenes Frequently illustrated upside down - so Frequently they look like a medusa, but swim ORAL side UP swim Your text does it right! Your Two types - those with tentacles for feeding, those without We have Mnemiopsis in lab. watch them swim, feed, We Mnemiopsis in dissect (preserved) and see dissect if you can find how their internal anatomy if differs from cnidarians differs 6 ...
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