HERE COMES A BIOLOGY NERD :D ...... who actually had to look up the answer to a side question in the episode, since arthropods aren't one of my major interests! x3;
Truth be told, the difference between insects and crustaceans is pretty nuanced -- but it's not just that "one lives in the water and the other doesn't."
Insects, crustaceans, myriapods (like centipedes and millipedes), and arachnids are all arthropods
("jointed feet"), members of a super
diverse phylum of animals which all share three main characteristics; an exoskeleton, pairs of jointed legs/appendages, and segmented bodies. Insects are a very specific
type of arthropod -- even though they're the most diverse group of animals on the planet. Crustaceans, less so. Crustaceans are like the "miscellaneous" class of arthropods. :B
To be an insect, an arthropod needs...
- A three-segmented body -- head, thorax, abdomen.
- Three pairs of legs -- no more, no less.
- Compound eyes.
- One pair of antennae.
If you don't have all of those, you're not an insect. But within those classifications? Go wild. Kind of amazing there are more than a million species of insect, isn't it? :3 Also, general guideline? If it's an arthropod and has wings, it's an insect. The other groups don't have 'em.
Crustaceans' membership guidelines are a little looser. Their main characteristic, aside from the general arthropod ones, is that if they have antennae, they have two pairs of them.
That's it. :B
Crustaceans are more defined by what they DON'T have as opposed to what they DO have. Like I said, it's kind of a catch-all category -- the easiest way to tell if you're an arthropod person is to check out their mouths. Insects and myriapods have well-developed mouthparts; arachnids have chelicerae, which are basically specialized "limbs" that act as little nippers and nibblers to help break up prey and/or inject venom. (Spider fangs are chelicerae. Scorpion pincers are not; the chelicerae are tiny things near the mouth. The pincers are pedipalps
, which are basically specialized appendages to help grasp and move food to the chelicerae. Spiders have them, too. But obviously differently-shaped and smaller. :B) Crustaceans tend to either be filter feeders, or have sets of mandibles/maxilla that are somewhere between insect mouths and chelicerae.
You were close in one respect, though! The vast majority of crustaceans are
aquatic, while the vast majority of insects aren't. :3 There are a few exceptions, though -- like woodlice/pillbugs, a type of cute little garbage-muncher that lives in moist places and chows down on decaying organic matter. Those are crustaceans. And there are aquatic insects, too, like whirligig beetles -- plus some insects, like mosquitoes (blech), lay eggs and live their early lives in the water.
Basically you guys were close, but not quite there -- and apparently you need to study arthropods pretty closely to be able to really tell the difference yourself. XP So good on ya! =w=d