The coccus refers to the bacteria that are spherical in their shape. They can be present in the pairs forming a row of chains of the spherical cells. The bacillus refers to the bacteria that are rod shaped. The bacillus bacteria are disease causing pathogens and are gram-positive. The aerobic bacteria uses oxygen and are generally rod-shaped. The spirillum refers to the spiral shape of the bacteria. They are rigid in their structure.
Hence, the answer is 'spirillum'.
The form of bacteria that appear curved like a spiral thick and rigid, or thin and flexible would be spirillum.
Spirilla bacteria (singular, spirillum) are bacteria that are spiral shape in their appearance.
Spiral-shaped bacteria can either be thick and rigid or thin and flexible.
Spirilla are generally Gram-negative and move with the aid of flagella. Many of the species are pathogenic in nature.
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