Description: The image shows a specimen of almost 500 µm length, with itâs typical, long tail. The compact, ovoid macronucleus measures app. 25x8 µm. The peristome in this specimen has a ratio of 1:5 with the bodylength. The organism is highly contractile (see other pictures of collection). It can easily be distinguished from the other, more frequently found species of the genus by itâs long tail (caudatum). Spir. minus, whose shape may sometimes look similar has a very different, moniliform macronucleus. Spir. teres on the other hand, whose macronucleus resembles the one of Spir. caudatum has a more cylindrical, cigar-like shape.