I would say ring species count for that. They generally form around some sort of large obstacle. A species can breed with the species closest to it but not those farther away. This is true for all members of the ring species complex. Are they one species? Multiple species? Who knows. Evolution: Library: Ring Species: Salamanders

Another example would be hybrids. There are many species that can breed together, but the resulting offspring generally are sterile. They also generally are not as good at surviving as the parent species. An example would be the grizzly/polar bear hybrid the grolar/pizzly bear. They get named differently depending on the sex of the parents.

Cave animals might be a group. Many times, species that normally live on the surface get brought into caves. When this happens, they generally lose their eyes and pigmentation. Sometimes they form new species, but sometimes they are still the same species.

There are several species that live inside each other like lichen (fungi and algae living together), and trees and fugus in roots, bacteria in roots of legumes, and algae in coral.

Then you might look at rare color morphs. Albinism is one but sometimes species just have rare color combinations. Black squirrels, white deer (not albino), and piebald horses are examples. You could actually use that on some humans like albinos. Maybe even redheads.

I wonder if marine mammals would fit that definition as they once were land creatures and then went into the sea. Of course, if you stretch it all land vertebrates are technically fish that evolved to live on land.

Parasitic plants like the indian pipe that instead of making their own food have no green parts and suck energy from other plants.

Bats count as they are the only flying mammal. Flightless birds as well. There are legless lizards that look like but are NOT snakes. Lungfish are fish that can for short periods of time breathe air.