Of course, since no living species has primitive traits from an earlier lineage and derived traits that are evident in subsequent lineages, no living species is transitional.
I'm not sure what you mean here; many living species share a mix of primitive and derived characteristics linking two clades. Monotremes share many primitve traits with reptiles, such as egg-laying and certain reptillian skeletal features; while sharing derived traits with other mammals such as fur and milk production.
I know you said that a living clade could be transitional but not a species, but the distinction seems unclear to me. A clade would be transitional because its members show a mixture of primitive and derived characteristics linking two groups; so why are the individual species showing this mixture not transitional? I don't see how the platypus differs so much from Archaeopteryx, which is not ancestral to modern birds and has derived traits not present in birds.
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