This is the 15537th most frequent Russian word.
пресмыкающиеся
Reptiles.
Here, 'пресмыкающиеся' is used as a noun describing a biological class of creatures.
Пресмыкающиеся, такие как ящерицы и змеи, обитают в тёплых регионах.
Reptiles, such as lizards and snakes, inhabit warm regions.
In this sentence, 'пресмыкающимся' is in its instrumental form, referring to a single creature belonging to the reptiles.
Он наблюдал за пресмыкающимся, которое пробралось в его сад.
He observed a reptile that made its way into his garden.
The term 'пресмыкающегося' is an adjective-like form describing a specific reptile species.