@bigfoob: Agreed on strat to try and kill the spider as quick as possible. Focus on it's weak point and if it tries to hide focus on the skull that will come at you no matter what then switch back to spider a few seconds later if you get the skull down quickly.
My best time is 158 right now and I feel like I'm stuck in a similar spot. What is the best strategy for when the centipede appears? I usually go right for the spider and get him down pretty quick but then centipede lives much longer then I feel like is intended because more spires start spawning. That generally overwhelms me and eventually leads to my downfall. I feel like if I can just figure out a way to get the centipede down quickly (while not giving spider a ton of gem snacks) then I will advance past this point.