Final answer:
The term for the absence of fingernails or toenails is 'anonychia'. It can be congenital or acquired. It is different from regular primate features like having opposable thumbs or big toes, five digits on the appendages, and having flat nails instead of curved claws.
Step-by-step explanation:
The term for the absence of fingernails or toenails is 'anonychia'. It is a rare condition that can be either congenital (present from birth) or acquired (developed after birth). Congenital anonychia usually occurs as part of a syndrome, while acquired anonychia can be the result of a disease, injury, or infection. In contrast, having opposable thumbs and (for non-human primates) opposable big toes, the presence of five digits (fingers or toes) on the appendages, and having flat nails instead of curved claws, are all typical features of primates, including humans.
Learn more about Anonychia