A teacher shows three worms: a leech ( Hirudinaria ), a marine worm with side flaps ( Nereis ), and…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A teacher shows three worms: a leech (Hirudinaria), a marine worm with side flaps (Nereis), and a roundworm (Ascaris). (a) Which two are in the same phylum? Give one feature they share. (b) Which of the three has a false body cavity? (c) Which of them are monoecious, and which dioecious?
Need a reminder? The key ideaShow
Platyhelminthes: flattened, acoelomate, mostly parasites with hooks and suckers, flame cells, hermaphrodite; Taenia, Fasciola, Planaria (regeneration). Aschelminthes: round in section, pseudocoelomate, muscular pharynx, dioecious; Ascaris, Wuchereria, Ancylostoma. Annelida: metamerically segmented, coelomate, nephridia, closed circulation, double ventral nerve cord; Nereis has parapodia and is dioecious; Pheretima and Hirudinaria are monoecious.
The worked solution
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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The same phylum. The leech and Nereis are annelids. Both have a body divided into metameres, a true coelom and nephridia.
Step 2. The false cavity. Ascaris is a roundworm, so it is pseudocoelomate.
Step 3. The sexes. The leech is monoecious. Nereis and Ascaris are dioecious.
Answer: (a) the leech and Nereis, both segmented annelids; (b) Ascaris; (c) the leech is monoecious; Nereis and Ascaris are dioecious.
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