What is long, thread-like extensions that grow from the protist to reach nutrients?

Flagella

Protists such as Choanoflagellates (closet of all species) have flagella at one end of their single celled body. These flagella's have several hair like structure which are dense and long and are known as microvilli. The flagella act as a pump and forces water across the microvilli and the microvilli then filter out food particles from the water.

Flagella or Flagellum for plural