Final answer:
Squids excrete waste through nephridia in their mantle cavity and produce ink as a defense mechanism.
Step-by-step explanation:
Squids excrete waste through a pair of nephridia located within the mantle cavity. The nephridia filter waste from body fluids, releasing it into the coelom. Squids also produce ink, which is stored in an ink gland located between the gills. The ink can be released into the water to distract predators or create a smokescreen for escape.