Other

Here is the list of taxonomical groups that secrete toxins/venom, but are not in the six major groups (snakes, spiders, scorpions, conidae, cnidaria and insects):

Vertebrates:
Platypus (order:Monotremata)
Squamata (including bearded dragon, gila monster, monitor)
Fish (including stonefish and toadfish) (infraclass:Teleostei)
Stingray (order:Myliobatiformes)

Invertebrates:
Centipetes (Chilopoda)
Starfish (order:Valvatida)