phylum cnidaria (radially symmetric, 2 cell layers in body) jellyfish and allies. these alternate 2...
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Phylum Cnidaria (radially symmetric, 2 cell layers in body)
Jellyfish and allies. These alternate 2 phases in their life cycle: the free-living medusoid phase (“jellyfish”), and a sessile hydroid phase.
Both feed by capturing planktonic food using tentacles armed with a cnidarian speciality, the class of stinging cell called nematocysts. Some are entangling, some inject barbed points to anchor, some inject toxins.
The main classes are:
• Hydrozoa: various medusoid radiations, often with several body forms fused into one animal ie Physalia physalis, the infamous, portugese man o’war (avoid!).
• Scyphozoa = jellyfish, Aurelia aurita in the common UK moon jelly (harmless to humans)
• Anthozoa: sessile forms: sea anemones, corals, sea fans
• Cubozoa: sea wasp
Cnidirians
• Overview: Life Without a Backbone
• Invertebrates– Are animals that lack a backbone– Account for 95% of known animal species
Figure 33.1
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Evolutionary Relationships of Cnidaria
The Radiate AnimalsTissue level of organization
• No anterior or posterior• Terms of direction defined based on the position of the
mouth• Oral/aboral ends• Biradial symmetry- single plane, passing through a
central axis, divides the organism into mirror images• Advantageous b/c sensory receptors evenly distributed.• Diploblasic tissue level organization- similar cells are
organized into tissues, and all cells are derived from two embryonical layers (ectoderm and endoderm/gastrodermis)
• A review of animal phylogeny
Ancestral colonialchoanoflagellate
Eumetazoa
Bilateria
Deuterostomia
Po
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Cn
ida
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Figure 33.2
• Exploring invertebrate diversity
PORIFERA (5,500 species)
A sponge
CNIDARIA (10,000 species)
A jelly
PLACOZOA (1 species) KINORHYNCHA (150 species)0.5 mm
A placozoan (LM) A kinorhynch (LM)250 µm
PLATYHELMINTHES (20,000 species) ROTIFERA (1,800 species)
A marine flatworm A rotifer (LM)
ECTOPROCTA (4,500 species) PHORONIDA (20 species)
Ectoprocts PhoronidsFigure 33.3
• Cnidarians have radial symmetry, a gastrovascular cavity, and cnidocytes
• All animals except sponges– Belong to the clade Eumetazoa, the animals
with true tissues
• Phylum Cnidaria– Is one of the oldest groups in this clade
• Cnidarians– Have diversified into a wide range of both
sessile and floating forms including jellies, corals, and hydras
– But still exhibit a relatively simple diploblastic, radial body plan
The Body Wall
• Two cellular layers• Epidermis- epithelio-muscular cells• Mesoglia- noncellular gel and is abundant
in the Medussa• Gastrodermis-
– gland cells for the production and release of enzymes.
– Flagellated nutitive muscular cells that contain food vacuoles
9-7
Fig. 9.9
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Cnidarian Body Wall
Phylum Cnidaria- Nematocysts
• Name comes from the presence of specialized cells used in defense, feeding and attachment.
• Cnidosytes contain stinging organelles called Nematocysts.
Tentacle
“Trigger”
Nematocyst
Coiled thread
DischargeOf thread
Cnidocyte
Prey
Figure 33.6
• Cnidarians are carnivores– That use tentacles to capture prey
• The tentacles are armed with cnidocytes– Unique cells that function in defense and the
capture of prey
Cnidocyte Structure and Nematocyst Discharge
9-8
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Fig. 9.10
• The basic body plan of a cnidarian– Is a sac with a central digestive compartment,
the gastrovascular cavity
• A single opening– Functions as both mouth and anus
• There are two variations on this body plan– The sessile polyp and the floating medusa
Mouth/anus
TentacleGastrovascularcavity
Gastrodermis
Mesoglea
Epidermis
Tentacle
Bodystalk
Mouth/anus
MedusaPolyp
Figure 33.5
Gastrovascular Cavity
• Receives and digest food
• Single opening serves as the mouth and anus
• Tentacles surrounding the opening aid in feeding.
CV cavity continue
• Simplicity of body plan
• Hydras and other cnidirians don not require a true circulatory systems
• Body wall two cell thick encloses CV cavity
• Serves both in digestion and distribution of substances throughout the body
• Extend to tentacles
• The phylum Cnidaria is divided into four major classes
Cladogram of Cnidarian Taxonomy
9-17
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Fig. 9.23
– Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa
(a) These colonial polyps are members of class Hydrozoa.
(b) Many species of jellies (classScyphozoa), including thespecies pictured here, are bioluminescent. The largest scyphozoans have tentaclesmore than 100 m long dangling from a bell-shaped body up to 2 m in diameter.
(c) The sea wasp (Chironex fleckeri) is a member of class Cubozoa. Its poison,which can subdue fish andother large prey, is more potent than cobra venom.
(d) Sea anemones and othermembers of class Anthozoaexist only as polyps.
Figure 33.7a–d
Alterations of Generations
• Typical cnidarian alternates b/w a hydroid stage (polyp) and a swimming medusa (jellyfish) stage.
• Polyp – assexual stage
• Medusa- sexual stage
• In some cnidarian classes either the polyp or the medussa is reduced or missing.
Generalized Cnidarian Life Cycle
Hydrozoans• Most hydrozoans
– Alternate between polyp and medusa forms
Feeding polyp
Reproductivepolyp
Medusabud
ASEXUALREPRODUCTION(BUDDING)
GonadMedusa
MEIOSIS
FERTILIZATION
SEXUALREPRODUCTION Egg Sperm
Developingpolyp
Portion ofa colonyof polyps
Maturepolyp
Planula(larva) Key
Haploid (n)Diploid (2n)1 mm
Zygote
Figure 33.8
A colony ofinterconnected
polyps (inset,LM) results
from asexualreproductionby budding.
1
Some of the colony’s polyps, equipped with tentacles, are specialized for feeding.
2 Other polyps, specialized for reproduction, lack tentacles and produce tiny medusae by asexual budding.
3
The medusae swim off, grow, and reproduce sexually.
4
The zygote develops into a solid ciliated larva called a planula.5 The planula eventually settles
and develops into a new polyp.6
Hydrazoa Obelia Structure and Life Cycle
9-10
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Fig. 9.12
Structure of Gonionemus Medusa
9-11
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Fig. 9.13b
CNIDARIA Class Hydrozoa
• Feather hydroid (Halocordyle disticha, formerly called Pennaria tiarella), from Bermuda
• Tiny, white tufts along lateral branches of the colony are individual polyps
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Photo Copyright © Diane R. Nelson
CNIDARIA Class Hydrozoa
• Fire coral (Millepora complanata), common in the Caribbean
• Polyps on surface and along edges (“fuzz”) are loaded with toxic stinging nematocysts
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Photo Copyright © Diane R. Nelson
CNIDARIA Class Hydrozoa
• Portuguese Man-o-War (Physalia physalia)
• This is a colony with several types of polyps: gastrozooids, gonozooids, and dactylozooids
• Highly toxic
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Photo Copyright © Diane R. Nelson
Scyphozoans
• In the class Scyphozoa– Jellies (medusae) are the prevalent form of the life
cycle– Polyp reduced or absent– Gametes produced gastrodermally– Cnidocytes present in gastrodermis and epidermis– Marine
– Examples- aurelia
Structure of Scyphozoan Medusa
9-12
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Fig. 9.15
Source: After L. H. Hyman, Biology of the Invertebrates, Copyright © 1940 McGraw-Hill Publishing Co.
Aurelia Life History
9-13
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Fig. 9.16
CNIDARIAClass Scyphozoa
• Sea thimble jellyfish (Linuche unguiculata), Honduras
• Tiny jellyfish (< 1 inch) that swarm in the spring
• Adults and larvae (“sea lice”) may cause a severe skin reaction in humans
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Photo Copyright © Diane R. Nelson
CNIDARIA Class Scyphozoa
• Upside down jellyfish (Cassiopea xamachana) from Bermuda, with zooxanthellae
• This specimen is swimming up to the surface, where its reflection is visible
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Photo Copyright © Diane R. Nelson
CNIDARIA Class Scyphozoa
• Jellyfish (Mastigias sp., family Rhizostomeae) from Jellyfish Lake in Palau, western Pacific
• These jellyfish have lost their ability to sting and depend on zooxanthellae for nutrition
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Photo Copyright © Diane R. Nelson
Anthozoans
• Class Anthozoa includes the corals and sea anemones– Which occur only as polyps
Longitudinal Section of a Stony Coral Polyp
9-15
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Fig. 9.20
Structure of an Anemone
9-14
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Fig. 9.19
Charles Lytle and J. E. Wodsedalek, General Zoology Laboratory Guide, 11th ed., Complete Version, New York, McGraw-Hill. Reprinted by permission of The McGraw-Hill Companies.
CNIDARIA Class Anthozoa
• Sea fan (Subergorgia sp.) from the Solomon Islands
• This is a colony, with reticulated branches in one plane, at right angles to the prevailing current
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CNIDARIA Class Anthozoa
• Gorgonian sea fan (Plexuaridae) on a reef wall in Fiji
• Individual polyps in the colony filter plankton from the water column
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CNIDARIA Class Anthozoa
• Polyp of a tree fern or palm coral (Clavularia sp.) with pinnate tentacles, in the Solomon Islands
• Large sheets of these polyps are attached by a common stolon to the substrate
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Photo Copyright © Diane R. Nelson
CNIDARIA Class Anthozoa
• Divaricate tree coral (Dendronephthya sp.), from Fiji
• These bushy or tree-like soft corals (alcyonaceans) are found only in the Pacific
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CNIDARIA Class Anthozoa
• Close-up of an alcyonacean tree coral (Dendronephthya sp.)
• Spicules, the small white rod-shaped structures, are embedded in the tissue and aid in supporting the colony
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CNIDARIA Class Anthozoa
• Corky sea finger (Briareum asbestinum), common in the Caribbean
• Sea rod in front has polyps extended, while rod in back has polyps retracted, revealing purple color
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CNIDARIA Class Anthozoa
• Sea anemone (Heteractis sp.) from Fiji
• Note column of anemone and tentacles along margin
• This anemone may be host to symbiotic anemonefish
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CNIDARIA Class Anthozoa
• The giant anemone or purple-tipped anemone (Condylactis gigantea) often harbors cleaning shrimp among its tentacles
• Common in Bermuda and the Caribbean
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CNIDARIA Class Anthozoa
• Aerial view of coral reefs in Fiji
• Dark blue on right is deep water
• White is the edge of the reef
• Lighter color is the reef flat
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CNIDARIA Class Anthozoa
• Extended slender polyps of the stony coral Goniopora sp., found in Fiji and the western Pacific
• Polyps are extended during the day
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CNIDARIA Class Anthozoa
• Orange cup coral (Tubastraea coccinea) from Bonaire in the Caribbean
• These ahermatypic corals extend their polyps at night to feed on plankton
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CNIDARIA Class Anthozoa
• Coral bleaching in star coral (Montastrea annularis) in the Caribbean
• Golden brown color indicates healthy tissue
• White area has lost zooxanthellae
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CNIDARIA Class Anthozoa
• Coral bleaching in star coral (Montastrea annularis) in the Caribbean
• Loss of zooxanthellae due to higher water temperatures results in lighter color
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CNIDARIA Class Anthozoa
• Close-up of the raised corallites of Caribbean elliptical star coral (Dichocoenia stokesii) in the daytime
• Polyps are extended at night to feed on plankton
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Photo Copyright © Diane R. Nelson
CNIDARIA Class Anthozoa
• Close-up of giant star coral (Montastrea cavernosa) with polyps extended at night to feed on plankton
• Common in the Caribbean
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CNIDARIA Class Anthozoa
• Sea pen (Pteroeides sp.) from the Solomon Islands
• This is a colony that lives anchored in the sand, turning at right angles to the prevailing current
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Class Cubozoa
A few a lethal to humans - NEVER EVER swim with box jellies (sea wasps)
Characteristics of Ctenophora
1)Radially or biradial Symmetrical. 2)Body multicellular, few tissues, some organs and organelles. 3)Body contains an internal cavity and a mouth and anal pores. 4)Swims by means of plates of cilia (the combs) 5)Reproduction mostly sexual as hermaphrodites, occasionally asexual. 6)Has a well developed subepidermal nerve net. 7)Has a distinct larval stage which is planktonic. 8)Lives in marine environments. 9)All are carnivorous.
Ctenophore Mnemiopsis
9-16
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Fig. 9.22
Ctenophora Anatomy
• Comb Jellies
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