๐ฆ๐ท๏ธ๐ฆ Arthropods: Crustaceans, Arachnids & Insects
What Are Arthropods?
Arthropods are animals with exoskeletons (external skeletons made of chitin), segmented bodies, and jointed legs. The word "arthropod" literally means "jointed foot" (from Greek: arthron = joint, podos = foot).
The phylum Arthropoda is the largest phylum in the animal kingdom, encompassing about 84% of all known animal species. Scientists estimate there are at least 5.5 million insect species alone!
๐ฌ The Three Key Groups
| Feature | ๐ฆ Insects | ๐ท๏ธ Arachnids | ๐ฆ Crustaceans |
|---|---|---|---|
| Body Segments | 3 (Head, Thorax, Abdomen) | 2 (Cephalothorax, Abdomen) | 2โ3 (Cephalothorax, Abdomen) |
| Legs | 6 legs (3 pairs) | 8 legs (4 pairs) | 10+ legs (5+ pairs) |
| Antennae | 1 pair | None โ | 2 pairs |
| Wings | Usually 1โ2 pairs | None โ | None โ |
| Eyes | Compound eyes | Simple eyes (up to 8) | Compound eyes (often on stalks) |
| Mouthparts | Mandibles | Chelicerae (fangs) & pedipalps | Mandibles |
| Habitat | Mostly terrestrial | Mostly terrestrial | Mostly aquatic |
| Examples | Butterflies, beetles, ants, bees | Spiders, scorpions, ticks, mites | Crabs, lobsters, shrimp, crayfish |