Arachnida – Spiders & scorpions

Web weavers and fang bearers

Arachnida, one of the first terrestrial animals, with four pairs of legs, basic eyes, and fang-tastic mouthparts. No antennae or wings – they keep it simple and stylish!

Arachnids typically have a body divided into two parts: a front part (*cephalothorax) with mouthparts, sensory organs, and legs, and a back part (abdomen) for digestion and reproduction. The arachnid skeleton is hydraulic. As an alternative to tracheae, the basic arachnid converts carbon dioxide into oxygen using two (or four) pairs of book lungs.

The majority of arachnids are terrestrial, yet their evolutionary history is rooted in marine environments. The Early Devonian (400 Ma) and Late Silurian (414 Ma) are the earliest known periods for terrestrial arachnids.

Today’s taxonomy of Arachnids includes about 640 families, 9000 genera, and around 100,000 identified species. The diversity of arachnids is astounding, yet it’s believed to be a small fraction of the class’s actual diversity.