Mr. Morales is teaching a lesson on classification. He says that spiders are classified as a different group than insects because they have eight legs instead of six legs. He explains that spiders evolved first. Mr. Morales also says that having eight legs is the derived trait that separates the two groups. Antonio thinks Mr. Morales is wrong. Which piece of information is Antonio considering?
Answers
Arachnids have the following traits :
They have two body parts.
They have eight legs unlike insects which have 6 legs.
They have no wings.
These traits distinguish them from insects.
The information that Antonio is doubting us the statement that spiders differences are as a result of being first to evolve.
This is because the evolution of one species is independent of the other species.
No. Spiders are arachnids There are a number of key differences between arachnids and insects.
Insects have three body segments: the head, thorax and abdomen. Arachnids have two body segments: the cephalothorax and abdomen.
Insects have six legs; arachnids have eight.
Insects have compound eyes; arachnids have simple eyes.
Insects have antennae. Arachnids have pedipalps.
Many insects have wings; no arachnid has wings.
Insects have jaws. Arachnids have fangs.
Insects undergo some form of metamorphosis (a change from immature to mature form); arachnids do not, although they do molt their exoskeletons.
When in doubt, count the legs. It’s the easiest indicator for lay people to determine whether you’re looking at a spider ot an insect. Some spiders are quite good at mimicry.
You could be forgiven for thinking this was an ant, but if you look closely, you can see it has eight legs, only two body segments, and multiple simple (rather than compound) eyes.