Final answer:
Homoplasy in Old and New World monkeys, which have evolved similar traits independently, is not designated by a unique term; it is simply referred to as homoplasy or convergence.
Step-by-step explanation:
The phenomenon of homoplasy, where the gain or loss of the same trait occurs independently in separate lineages over the course of evolution, is observed in Old World and New World monkeys. This convergence can be attributed to similar environmental pressures leading to analogous structures or behaviors that are not derived from a common ancestor. In the case of Old and New World monkeys, the specific homoplasy isn't labeled with a unique term beyond the general concept of homoplasy or convergence.
Both groups of monkeys, the Platyrrhini (New World monkeys) and the Catarrhini (Old World monkeys), experienced parallel evolutionary changes due to their separate adaptive radiations. Despite originating from a common ancestor during the Oligocene epoch, they underwent divergent evolution once isolated. The New World monkeys evolved features such as prehensile tails as an adaptation to their arboreal lifestyle, whereas Old World monkeys have evolved different traits, like cheek pouches or ischial callosities in some species.
Examples of homoplasy can be seen in distinct evolved characteristics in the Old and New World monkeys that arose because they inhabited similar ecological niches rather than inheriting these traits from a recent common ancestor. This evolutionary process demonstrates how similar adaptations can evolve in species that are not closely related due to similar selective pressures.