Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
Students sink a jar into the ground overnight to trap small animals. In the morning it holds insects and spiders. (a) How many legs are there in the jar? (b) Name the phylum of both animals, and the feature that gives it its name.
Arthropoda: the largest phylum; chitin exoskeleton, jointed appendages, head, thorax and abdomen, open circulation, malpighian tubules; insects have 6 legs, spiders 8, crabs 10. Mollusca: head, muscular foot, visceral hump, mantle, radula, usually a shell; Pila, Pinctada, Sepia, Loligo, Octopus. Echinodermata: calcareous ossicles, water vascular system, radial adult and bilateral larva, no excretory system; Asterias, Echinus, Antedon, Cucumaria, Ophiura. Hemichordata: proboscis, collar and trunk; proboscis gland; Balanoglossus, Saccoglossus.
Have you tried it?
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 legs. legs.
Step 2. The phylum. Both are arthropods. The name means jointed feet: their legs have joints.
Answer: (a) legs; (b) Arthropoda, named for its jointed appendages.
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