In eukaryotes, the ribosome consists of four main types of rRNAs: 18S, 5.8S, 28S, and 5S. The small ribosomal subunit (40S) contains the 18S rRNA, while the large ribosomal subunit (60S) is composed of 5.8S, 28S, and 5S rRNAs. Each of these rRNAs has specific roles in maintaining the structure and function of the ribosome.