Cnidarian Basics
This type of symmetry allows a cnidarian to interact with its environment from many directions around a central point.
What is radial symmetry?
This cnidarian body form is generally attached to a surface.
What is the polyp form?
In a jellyfish, these structures contact and help capture prey in the water.
What are tentacles?
Ctenophores are commonly known by this name.
What are comb jellies?
This term refers to an organism's body structures and physical form.
What is morphology?
These specialized stinging cells found on cnidarian tentacles are used in prey capture and defense.
What are cnidocytes?
This cnidarian body form is generally free-swimming.
What is the medusa form?
A jellyfish moves forward when this structure contracts and pushes water behind the animal.
What is the bell?
Ctenophores have eight rows of these structures along their bodies.
What are comb rows?
This term describes the study or interpretation of evolutionary relationships among organisms.
What is phylogeny?
Jellyfish, sea anemones, and corals belong to this animal phylum.
What is Cnidaria?
Food enters a cnidarian through this opening, which is surrounded by tentacles in many species.
What is the mouth?
The bell helps with movement, while the tentacles and cnidocytes primarily help perform this function.
What is prey capture/feeding?
Rather than using bell contractions like jellyfish, ctenophores move using many tiny hairlike structures called these.
What are cilia?
Scientists compare traits such as cnidocytes, comb rows, and feeding structures because these characteristics provide evidence for this process.
What is classification?
A zoologist observes an animal with radial symmetry and tentacles containing stinging cells. These observations provide evidence that the animal belongs to this group.
What are cnidarians?
This internal cavity receives food and is an important structure included in the Cnidarian model.
What is the gastrovascular cavity?
Complete this structure-function relationship: cnidocyte → stinging → ________.
What is prey capture or defense?
Instead of the stinging cnidocytes characteristic of cnidarians, ctenophores can capture prey using these sticky cells.
What are colloblasts?
Two animals are both soft-bodied and aquatic. One has cnidocytes; the other has comb rows and colloblasts. Which evidence is more useful for classification: their shared habitat or their specialized structures?
Their specialized structures are more useful evidence.
A student classifies a transparent marine animal as a cnidarian only because it looks like a jellyfish. Explain the problem with this reasoning.
Appearance alone is insufficient; the student should look for diagnostic structures such as cnidocytes and other morphological/behavioral evidence.
A model shows tentacles arranged in a circle around a central mouth. This body organization/symmetry demonstrates this major cnidarian characteristic.
What is radial organization/radial symmetry?
A jellyfish's bell contracts while its tentacles trail through the water. Explain how these two structures work together to increase survival.
The bell provides movement while the tentacles/cnidocytes encounter and capture prey, linking locomotion with feeding.
A transparent organism has eight shimmering rows, moves using cilia, and captures prey using sticky cells. Classify the organism and give the strongest evidence.
It is a ctenophore; the strongest evidence is its comb rows/ciliary movement and colloblasts rather than cnidocytes.
Site A has 12 jellyfish at 24°C, Site B has 38 at 27°C, and Site C has 71 at 29°C. What pattern is present, and what should a scientist avoid concluding from these data alone?
Jellyfish numbers increase as temperature increases in the data; scientists should not claim temperature caused the increase without additional evidence.