Input (grade 13): The cells typically have two slightly unequal flagella, both of which are smooth, and a unique organelle called a haptonema, which is superficially similar to a flagellum but differs in the arrangement of microtubules and in its use.
Output (grade 11): The cells typically have two slightly unequal flagella and a unique organelle called a haptonema. This is is superficially similar to a flagellum, but differs in its arrangement of microtubules, and in its use.