24 Questions
What triggers the release or firing of nematocysts?
Tactile stimulation of the cnidocil
What is the function of the annulus in Hydra?
Gives flexibility and support to the hydrocaulus
What is the primary function of nematocysts in Cnidarians?
Capturing and digesting prey
How many monophyletic clades are Cnidarians classified into?
Two
What is the shape of the body of Aurelia aurita?
Bell-shaped
What is the function of the cnidocyte?
Produces nematocysts for capturing prey
What is the symmetry type exhibited by Cnidarians?
Radial symmetry
How many species of Cnidarians are estimated to exist?
Around 10,000
What is the characteristic of the body wall of Cnidaria?
It consists of two living layers: epidermis and gastrodermis, and a nonliving mesoglea in between.
What is the function of the gastrovascular cavity in Cnidaria?
It serves as a digestive tract where extracellular digestion takes place.
What is the characteristic of cnidocytes in Cnidaria?
They are stinging cells that contain nematocysts.
What is the characteristic of the nematocysts in Cnidaria?
They are stinging organelles that contain barbs or spines at the base of the long, coiled thread.
What is the characteristic of the body plans of Cnidaria?
They have radial symmetry.
What is the characteristic of the life cycle of many Cnidaria?
They are dimorphic, exhibiting both body plans during their life cycle.
What is the habitat of most Cnidaria?
Marine.
What is the example of a polymorphic Cnidaria?
Physalia physalis (Portuguese Man-of-War).
What is the function of cnidocil?
To sense mechanical stimuli and elicit nematocyst discharge
What is the term for the 'stinging cells' that contain a nematocyst?
Cnidocyte
What is the function of zooxanthellae in scleractinian corals?
To produce oxygen and help remove waste
What is the term for the stalk-like structure that contains the mouth and connects to the coelenteron?
Manubrium
What is the term for the free-swimming, flattened, ciliated, and bilaterally symmetrical larval form of cnidarians?
Planula
What is the term for the organelle within a cnidocyte that is used for prey capturing and defense?
Nematocyst
What is the term for a strobilating polyp that produces young adult medusae called ephyra?
Strobili
What is the term for a type of medusa that has a velum?
Craspedote
Study Notes
Phylum Cnidaria
- Radial symmetry and diploblastic (develop from two embryonic layers: ectoderm and endoderm)
- Two distinct body plans: polyp (sessile) and medusa (motile)
- Body wall consists of: epidermis, gastrodermis, and non-living, jelly-like mesoglea
- Gastrovascular cavity: open only on one end (mouth), serves as digestive tract for extracellular digestion
Characteristics of Cnidarians
- Presence of stinging cells called cnidocytes, often located on tentacles, around mouth, and in gastrodermis
- Cnidocytes contain stinging organelles called nematocysts, which may contain barbs or spines
- Nematocysts are triggered by tactile stimulation of cnidocil (hair-like projection)
- Release of nematocysts can entangle or pierce prey, injecting toxic substances to paralyze
Nerve System and Symmetry
- Nerve net system complements radial symmetry
- Two monophyletic clades: Medusozoa and Anthozoa
Hydra and Other Cnidarians
- Hydra: exhibits dimorphism, has spermaries and ovary, and annulus provides flexibility and support to hydrocaulus
- Obelia: colonial hydroid, exhibits dimorphism
- Aurelia aurita: bell-shaped, saucer-shaped medusa with eight marginal lobes and stinging tentacles
- Hydra budding: a method of reproduction
Corals and Zooxanthellae
- Mutualistic relationship: coral provides CO2 and water for photosynthesis, and zooxanthellae produce oxygen and help remove waste
- Ecological values of coral reefs:
- Protect coastlines from storms and erosion
- Provide ecosystem for underwater life
- Provide source of livelihood for local communities (fishing, tourism)
Cnidarian Terminology
- Nematocyst: organelles within a cnidocyte used for prey capturing and defense
- Cnidocil: mechanosensory receptor that elicits nematocyst discharge
- Cnidocyte: "stinging cells", an explosive cell containing a nematocyst that delivers a sting
- Planula: free-swimming, flattened, ciliated, and bilaterally symmetrical larval form of cnidarians
- Strobili: a strobilating polyp that produces young adult medusae called ephyra
- Manubrium: a stalk-like structure that contains the mouth and connects to the coelenteron
- Hydrotheca: a structure that provides protection to the medusae
This quiz covers the basics of Phylum Cnidaria, including their characteristics, body plans, and development. Learn about radial symmetry, diploblastic development, and the differences between polyp and medusa body plans.
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