ABSTRACT
Ribosomal gene sequence comparisons suggest that one of the most primitive eukaryotic cells studied to date belongs to the genus Giardia (Sogin et al., 1989). Giardia has ribosomal genes which much more closely approximate the sizes of those in prokaryotes than those in eukaryotes (Sogin et al., 1989), and they lack mitochondria, microbodies and a detectable Golgi apparatus (Friend, 1966). These apparently ancient flagellates have successfully parasitized a wide variety of vertebrates including humans (Meyer and Jarroll, 1980). In humans, giardiasis is considered one of the most important water-borne infectious diseases (Craun, 1986).
