genus of large, pear-shaped zooflagellate protozoans; they are intestinal inhabitants of termites (termite). The species H. tusitala, whose chromosomal behaviour during nuclear division has been studied, ranges from 130 to 200 micrometres (0.005 to 0.008 inch) in length and has five spiraling bands of flagella running posteriorly along the body. The chromosomes of H. tusitala, which may reach a length of 50 micrometres (0.002 inch), are larger than many small protozoans. Nuclear structural changes and chromosomal behaviour during division in H. tusitala provide a pattern for comparison with nuclear division in other protozoans; these differences are useful in determining taxonomic relationships.