Complex sentence: Males have black, spiny nuptial pads on their thumbs and'accessory' spines on their chests, these spines are used in amplexus, in order for the males to attain a better grip of the female.
Split into simpler sentences: Males have black, spiny nuptial pads on their thumbs and'accessory spines' on their chests. These spines are used in amplexus, in order for the males to attain a better grip on the female.