★ Must-know
Animals may be diploblastic, with two germ layers, or triploblastic, with three germ layers.
Animals may show radial symmetry, in which body parts are arranged around a central axis, or bilateral symmetry, in which the body can be divided into two equal halves.
Animals may be acoelomate, pseudocoelomate, or coelomate according to the presence and type of body cavity.
Further detail
Radial symmetry radiates around a centre, whereas bilateral symmetry divides the body into two sides.
★ Must-know
Cnidarians include Hydra and may have sessile polyp and free-swimming medusa forms.
Molluscs possess a mantle cavity and a radula, and the diagram associates them with excretion and respiration.
Hemichordates are characterized by a proboscis and stomochord.
Further detail
📌 Cnidarians may reproduce asexually in the polyp form and sexually in the medusa form.
Cnidaria → Platyhelminthes → Mollusca → Hemichordata
1. How many germ layers does a triploblastic animal possess?
2. An animal whose body parts are arranged around a central axis has which type of symmetry?
3. Which classification describes animals according to the presence and type of their body cavity?
What germ layers do diploblastic animals have?
Two germ layers.
How many germ layers do triploblastic animals have?
Three germ layers.
What type of symmetry arranges body parts around a central axis?
Radial symmetry.
Which symmetry divides the body into two equal halves?
Bilateral symmetry.
What determines if an animal is acoelomate, pseudocoelomate, or coelomate?
The presence and type of body cavity.
Which animals are included in the Cnidarian group?
Hydra and related species.
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