10. Cnidaria Flashcards
Spherical Symmetry
Any plane passing through the center divides the body into mirrored halves
- Floating and rolling
Radial Symmetry
Body divided into similar halves by more then two planes passing through the longitudinal axis
- Can interact with environment in all directions
- Sponges, Jellyfish, SeaUrchins
- Sessile, Free Floating or weakly swimming animals
Biradial Symmetry
Variant of radial
- Radial symmetry with an aspect of bilateral symmetry
- Comb Jellies(ctenophora) tentacles
Bilateral symmetry
Divided along sagittal plane into two mirror portions forming right and left halves
- Much better for directional movement
- Associated with cephalization
- Mouth at front allows efficient feeding
Cephalization
The differentiation of the head region and the concentration of nervous tissues and sense organs in the front area
Frontal plane
Coronal Plane
- Divides body into dorsal and ventral halves
Sagittal Plane
Divides body into left and right
Transverse plane
Cross section
- Divides body into anterior and posterior halves
Anterior
Head end
Posterior
Tail end
Dorsal
Back side
Ventral
Belly side
Medial
Midline of body
Lateral
Left and right sies
Distal
Parts farther from the middle of the body
Proximal
Parts nearer from the middle of the body
Cnidaria & Ctenophora similarity
- Radial / Bilateral symmetry
- Cell-tissue level organization
- Diploblastic
- Blind gut
Cnidaria
- Mostly sessile or slow moving
- Efficient predetors
- Algae are frequent mutualists
- Mostly marine, some fresh water
- Abundant in shallow marine habitat
Two morphological types of Cnidarians
Polyp - Sedentary or sessile
Medusa - Floating or free-swimming
Sessile
Fixed in one place
Sedentary
Little movement
Substratum
Solid surface
Polyp form of Cnidarian
- Tube shape
- Sedentary or Sessile
- Mouth surrounded by tentacles
- Can be attached to substratum by pedal disc
Medusa form of Cnidarian
- Umbrella - Shaped
- Floating or free swimming
- Mouth centered on concave side
- Tentacles extend from rim of umbrella shape
Commonality of Cnidarian forms
- Diploblastic
- mesoglea between two tissue layers
- Mesoglea is thicker in the medusa form - buoyancy
Cnidarian Respiration
Diffusion
Cnidarian Digestion
- Mouth opens into gastrovascular cavity
- Blind gut
- Extra & Intracellular digestion
- Undigested material carried back into the cavity by amoeboid cells
Cnidarian Reproduction
- Planula Larva
- Planula settles and metamorphoses into a polyp
- Polyp reproduces sexually or asexually
- Colonies form when polyps reproduce asexually but stay attached
- Polyps within colony specialize for certain functions
- Medusae reproduce sexually
Locomotion
- Some polyps are sessile
- Hydra and sea anemones can move slowly by gliding on pedal disc
- Sea anemones occasionally swim
Cnidocyte
Cell that holds cnida
Cnida
Stinging organelle
- Nematocyst - Most common type of cnida
- Many nematocyst have a toxin which paralyzes prey
Cnidocil
Triggers the nematocyst to fire
Hydrozoa
Typically asexual polyp and sexual medusa
- Hydra has only polyp
- Others only have medusa
Scyphozoa
True jellyfish
- Dioecious
- Internal fertilization
- Medusa and polyp during life cycle
Life cycle of Aurelia
- Sperm Fertilizes egg in Gastric Pouch
- Zygote develops on arms of female
- Planula larva attaches and becomes a scyphistoma (Polyp form)
- Scyphistoma can bud to form other polyps (asexual reproduction)
- Become a strobila
- Releases saucerlike buds called ephyrae
- Ephyrae grow into mature jellyfish (mature form)
Cubozoa
“box jellyfish”
- Medusa is prominent form - polyp is often uncharacterized
- Medusa bells are almost square
- Tentacles occur at corners of square
- Strong swimmers and predators
- String from some species can be fatal to humans
Anthozoa
- Polyps with a flower-like appearance: sea anemones, corals, sea fans
- No medusa stage
- Sexual and asexual reproduction occur in polyp phase
- All marine
- Solitary or colonial
Ctenophora
- Biradial symmetry
- All marine, especially in wam waters
- Commonly called “Sea walnuts” or “Comb Jellies”
- No nematocysts except Haeckelia rubra
Symbiosis of Clownfish & Cnidarians
Obligate mutualism
- Clownfish cannot survive without anemones
Facultative mutualism
- Anemones can survive without clownfish
Anemone & Clownfish Benefits
Benefit to clownfish - Protection - Hide from predators in the tentacles Benefit to Anemone - Clownfish chases other fish and protect anemone from being eaten - Nitrogen supply through ammonia - Water circulation increased
Crab-Cnidarian symbiosis
Crabs have anemones on claws - genus Lybia
- Steal anemone if missing and tear in half - inducing asexual reproduction
Symbiosis with Zooxanthellae
Coral reefs get their colors from mutualistic zooxanthellae algae
- Energy from the photosynthetic leftovers
Coral bleaching is caused by the death of Zooxanthellae algae
