Spirostomum is one of the largest ciliates. Stretched, these heterotrich ciliates can be more than a millimetre in length. Spirostomum is particularly interesting because it is capable of the fastest contraction known. These two ciliates are conjugating, they exchange genetic material. It is not reproduction since there are no offspring. After the process they are rejuvenated.

See more images of conjugating ciliates.

Part of the Collection of the Ciliate Centre of the Micropolitan Museum © Wim van Egmond