Technically, there could be thousands of answers, as two animals can have the exact same hierarchy except for the species. There can not necessarily be two "closest related species".
There are, however, instances where animals of the same species have made different adaptations. Such as in one type of hummingbird living in South America, the female has a longer, more curved beak than that of the male because they feed on different flowers.
Entamoeba coli is most closely related to Entamoeba histolytica because they both belong to the same genus, Entamoeba. Escherichia coli is a different genus and is more distantly related to the Entamoeba species.
Organisms in the same genus are most closely related to one another according to Linnaeus's groupings.
Naturalism is most closely related to realism, as it also aims to depict life as it is, emphasizing accurate representation of everyday life and characters within a narrative. Both movements seek to portray human experiences with honesty and authenticity.
Clasifiaction
species that have very similar resource requirements and niche preferences, leading to direct competition for limited resources, ultimately resulting in the elimination or exclusion of one species by the other.
Humans and chimpanzees are the two species that are most closely related to each other.
Humans are most closely related genetically to chimpanzees.
Humans and chimpanzees are the two species that are most closely related in terms of genetic similarity.
Amphibians and avians are the most closely related species to reptiles.
Horses are related to one-hoofed mammals
The classification with the most similar species is the genus, as it groups species that are closely related and share common characteristics..species within the same genus are more closely related to each other than species in different genera.
Thesus monkey is the most closely related to Humans because it has the least number of differences in cytochrome c.
Choanoflagellates are the group of protists most closely related to animals, including humans. Choanoflagellates are known for their distinctive cell morphology.
The taxon that includes organisms that are most closely related is a species. Organisms within the same species share a high degree of genetic similarity and can interbreed to produce fertile offspring.
Humans are most closely related to chimpanzees and bonobos, sharing a common ancestor with them around 6-7 million years ago.
Come out, appear, step into sight...
The okapi is most closely related to the giraffe. Family Giraffidae.