Bacteria that look rod-shaped are called bacillus. Different types of bacillus are-
(i) Monobacillus : Rod shaped bacteria are called monobacillus if they are single. For example- Bacillus albus, Escherichia coli.
(ii) Diplobacillus : When rod-shaped bacteria are arranged in pairs, they are called Diplobacillus. Lactobacillus, Corynebacterium diptheriae, Moraxella lacunata, Diplobacillus.
(iii) Streptobacillus: Rod-shaped bacteria are called Streptobacillus if they are arranged in chains. For example- Bacillus tuberculosis, Streptobacillus moniliformis.
(iv) Palisadebacillus : If the rod-shaped bacteria are parallel to each other and form a structure like oleic tissue, it is called palisade bacillus. For example, Lampropedia sp.
(v) Coccobacillus: If the bacteria are elongated or ovoid, they are called coccobacillus. For example – Salmonella, Mycobacterium, Coxiella burnetti.
3. Spirillum: Viruses that have a squiggly or coiled appearance are called Spirillum bacteria. For example, Spirillum minus, Treponema.