Question

cladists define a species as a group of organisms sharing a set of unique, derived features that sets them apart form all other such groups. this way of defining species exemplifies
the biological species concept.
the phylogenetic species concept.
the phenetic fossil species concept.
the aristotelian species concept.

Explanation:

The phylogenetic species concept defines species based on unique, derived features (synapomorphies) that distinguish them from other groups. Cladists use this approach focusing on evolutionary relationships and shared - derived characteristics. The biological species concept is based on reproductive isolation, the phenetic fossil species concept on overall similarity in fossils, and the Aristotelian species concept is an ancient view not related to derived features in the cladistic sense.

Answer:

the phylogenetic species concept.