Condylostoma

Condylostoma are very large elongated unicellular ciliates with lengths ranging from 176 to 1600 µm.[4][5] They also tend to be about 7 times longer than their width.[4][6] While the shape of the cell can vary depending on many factors, especially the amount and size of food vacuoles present, they are normally more rounded towards the middle of the cell and have a blunt posterior end. The relatively small buccal groove is about ⅓ the size of total body length and is present ventrally on the anterior part of the cell. The buccal groove is triangular. While there are no cilia inside the groove the surrounding “lips” are covered in cilia. Early papers describe a thin transparent undulating membrane around the buccal groove which is now known to be the adoral zone of membranes (AZM). These membranes can be composed of 70 to 200 polykinetids.[7] They have a very elastic thin pellicula (membrane) surrounding the cell which can be 2 to 8µm depending on the section. The cells are covered in longitudinal myonemes, which help make them contractile, and have trichocysts present in the posterior end of the cells. Being ciliates they are covered in cilia except in the buccal funnel.[4] The cilia are oriented following the myonemes in rows. While the number of kinetosomes do not change during interphase, the length of the kineties do, to accommodate for the cell's change in size.[7] Their cilia are long and slender, with the posterior cilia being the longest. Additionally, some research states that the ventral side of the cell has fewer, longer cilia than the dorsal end but this has been disputed.[1][4] Additionally many species were found to have at least one frontal cirrus with some having up to four present.[8] Looking at the interior of the cell, they are full of food vacuoles as well as cortical granules. They have a macronucleus with differing numbers of nodules ranging from 6 to 120.[1][4] The pellicle of the cells is rough and dark grey, with randomly dispersed granules directly below it. The cell itself is almost colorless but has a slightly grey or yellow tinge to it.[3] No contractile vacuole was observed at least in the marine species. The cells in this genus are notoriously hard to identify for two main reasons. First, there are many morphological differences between the species in this genus making it hard to identify them as belonging to the Condylostoma genus. Second, the species that have been described do not have as much detail as would be needed given the fact that there are few character states, otherwise known as traits, that can be used to identify cells as belonging to this genus.[4]

These are mostly benthic organisms that glide along the sediment. The gliding is done by beating the cilia throughout their body, and interestingly the dorsal cilia tend to beat more slowly than the rest. They mostly glide forward but can turn by adjusting the posterior end of the cell, making it act as a rudder. Their standard gliding velocity is around 1mm per 2.9 seconds but they can speed up to 3 times that velocity when stimulated.[4] Cells can also swim but are seldom seen doing this. They tend to swim in a spiral pattern due to the asymmetry of their body. When both gliding and swimming the organism has been observed to stop and move backwards when touching an object.[9]

Many ciliates use a slightly alternate genetic code compared to other eukaryotes. In the case of Condylostoma, stop codons have been reassigned to code for an amino acid .[6] For these new substitutions TAA and TAG code for glutamine and TGA codes for tryptophan. The question then becomes how does Condylostoma stop translation? The answer seems to be that these codons can function both as stop codons and as normal amino acid encoders. In this case whether or not translation is ended seems to be dependent on the location of the “stop codon” in the transcript and how close they are to the 3’ end of the mRNA.

Condylostoma tends to be fairly slow-growing when compared to other protists. They demonstrated to have a lifespan of around 6 days in their normal form, but that they could encyst if they were starved or stressed.[10] It is hypothesized that this is due to the fact that they feed mostly on algae. This is an abundant, yet seasonal food source, so they need to be able to survive during parts of the year when algae may not be present in high quantities, or may not be present at all. Division in these cells starts with the macronucleus beads fusing to form a band before they divide in two. Some of the polykinetids are passed onto the daughter cell and then renewed in the posterior position. Both the frontal cirri and paroral membranes need to be formed in the daughter cell.[3]