Word Origin and History for semi-Expand before vowels sem-, word-forming element meaning half, part, partly; partial, imperfect; twice, from Latin semi-half, from PIE *semi-half (cf. Sanskrit sami half, Greek hemi-half, Old English sam-, Gothic sami-half).
Well-known rodents include mice, rats, squirrels, prairie dogs, porcupines, beavers, guinea pigs, hamsters, gerbils and capybaras. Other animals such as rabbits, hares, and pikas, whose incisors also grow continually, were once included with them, but are now considered to be in a separate order, the Lagomorpha.
There are many different animal classes and every animal in the world belongs to one of them. The five most well known classes of vertebrates (animals with backbones) are mammals, birds, fish, reptiles, amphibians.They are all part of the phylum chordata -- I remember  chordata  by thinking of spinal chord. There are also a lot of animals without backbones.here are many different animal classes and every animal in the world belongs to one of them. The five most well known classes of vertebrates (animals with backbones) are mammals, birds, fish, reptiles, amphibians. They are all part of the phylum chordata -- I remember  chordata  by thinking of spinal chord.