A unique species of snail has been discovered in the Negev Desert. At night, these snails use a toothlike rasping organ in their head to scrape up porous limestone; they then digest the algae that lived in the rock pores. This scraping organ is the:

Radula

Explanation:

Radula is a structure found in mollusks which is used for the purpose of feeding and it is often considered to be like a tongue. It has minute teeth and chitinous in nature so mainly used for scraping and cutting of the food particles.

It has been also said in the question that the new species is snail that means it belongs to the phylum mollusca. And in the organisms of the phylum mollusca, Radula serves as the rasping organ.