Final answer:
The tongue-like, rasping organ in the head of many molluscs is the radula. It is equipped with chitinous teeth and used for shredding or scraping food, except in bivalves who lack this organ due to their filter-feeding nature.
"The correct option is approximately option A"
Step-by-step explanation:
The tongue-like, rasping organ in the head of many molluscs is the radula. This unique structure is responsible for the feeding habits of mollusks, as it assists in shredding or scraping food before it enters the digestive tract. The radula is equipped with chitinous teeth and is found in all groups of mollusks with the exception of bivalves, which are filter-feeders and thus do not require such an organ.
The role of the mantle, also significant in mollusks, is different as it is primarily involved in secreting the hard, protective shell of the mollusk. It creates the mantle cavity, which is utilized for various physiological processes including water circulation for filter feeding in certain groups. Other structures like the operculum and siphon also play roles in mollusk anatomy but are not related to the rasping function.
Herbivorous mollusks use the radula to scrape algae off surfaces, while predatory species may use it to drill into the shells of other mollusks or to process their prey. Thus, the radula is a versatile and essential organ for many mollusks, reflecting the great diversity within the mollusk phylum.