Video Transcript
Sea anemones belong to the phylum
Cnidaria. What defining characteristics do
organisms belonging to this phylum share? (A) These organisms only respire
anaerobically, and they can live on land or in the sea. (B) Their bodies consist of three
main layers of cells and are often surrounded by a hard exoskeleton. (C) Their bodies are segmented,
with each segment attached to appendages, and they do not possess a head. Or (D) their bodies consist of two
main layers of cells, they do not possess a head, and they have a mouth surrounded
by tentacles.
Organisms belonging to the phylum
Cnidaria have many characteristics in common. Let’s look at these answer choices
and eliminate those that are incorrect.
First, cnidarians are aquatic
organisms. They do not live on land, so we can
eliminate (A). Cnidarian bodies are composed of
two main layers, with the outer layer containing stinging cells. So, we can eliminate answer (B), as
cnidarians do not have three main layers. Finally, cnidarians do not have
body segments. They have appendages that surround
a mouth opening. So, we can eliminate answer (C)
because the appendages do not attach to body segments.
The correct answer is (D). Their bodies consist of two main
layers of cells, they do not possess a head, and they have a mouth surrounded by
tentacles.
