Mention the general characters of Arachnida.

Explanation

1) This includes, scorpions, spiders, ticks and mites.
2) Primarily they are all terrestrial.
3) Prosoma bears one pair of pre oral chelicerae, one pair of post oral pedipalps and four pairs of walking legs.
4) In spiders each chelicera bears a fang into which poison gland opens.
5) Abdominal appendages are modified into book lungs, spinnerets, pectines etc:
6). Telsun is usually absent. It is present as a sting in scorpions.
7) Respiration is by book fungs or tracheae. ,
8) Excretory organs are coxial glands and malpighian tubules.
9) Scorpions are viviparous.
10) Development is direct.