Arachnid is a giant spider.
Arachnid is book 11 and is part of series two: The Golden armour. Nanook helps Tom defeat Arachnid, and obtains the golden gauntlets.
Arachnid inhabits the caves underneath a mountain. He was once a resident of the peaks, but found food more plentiful further toward the villages. He then migrated into the caves under the foothills.
Arachnid is very fast and agile for his size, and can hurl strands of webbing at prey.