Hypotrich
Encyclopedia
The hypotrichs are a group of ciliate
protozoa, included among the spirotrich
s. Most are oval in shape, with a rigid pellicle, and have cirri (bundles of cilia) distributed in isolated tufts on the ventral surface of the cell. Some also have dorsal cilia, which function as sensory bristles. Euplotes and Aspidisca are common genera. Like other ciliates, hypotrichs reproduce by cell division
and conjugation.
The hypotrichs were first defined by Friedrich von Stein in 1859. Originally the stichotrich
s, which also have cirri, were included here, but they were separated out by Small & Lynn, 1981, who placed the restricted hypotrichs among the Nassophorea
because of various peculiarities in their infraciliature. More recent schemes reverse this move, and some molecular studies suggest they may be paraphyletic to the stichotrichs as currently defined.
Ciliate
The ciliates are a group of protozoans characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagella but typically shorter and present in much larger numbers with a different undulating pattern than flagella...
protozoa, included among the spirotrich
Spirotrich
The spirotrichs are a large and distinctive group of ciliate protozoa. They typically have prominent oral cilia in the form of a series of polykinetids, called the adoral zone of membranelles, beginning anterior to the oral cavity and running down to the left side of the mouth. There may also be...
s. Most are oval in shape, with a rigid pellicle, and have cirri (bundles of cilia) distributed in isolated tufts on the ventral surface of the cell. Some also have dorsal cilia, which function as sensory bristles. Euplotes and Aspidisca are common genera. Like other ciliates, hypotrichs reproduce by cell division
Cell division
Cell division is the process by which a parent cell divides into two or more daughter cells . Cell division is usually a small segment of a larger cell cycle. This type of cell division in eukaryotes is known as mitosis, and leaves the daughter cell capable of dividing again. The corresponding sort...
and conjugation.
Stichotrich
The stichotrichs are a group of ciliate protozoa, included among the spirotrichs. Like the hypotrichs, with which they were originally classified, they have body cilia fused into cirri, but these are mostly arranged into rows, running along the ventral surface or edges of the cell. Most...
s, which also have cirri, were included here, but they were separated out by Small & Lynn, 1981, who placed the restricted hypotrichs among the Nassophorea
Nassophorea
The Nassophorea are a class of ciliate protozoa. Members are free-living, usually in freshwater but also in marine and soil environments. The mouth is anterior ventral and leads to a curved cytopharynx supported by a prominent palisade of rods or nematodesmata, forming a structure called a cyrtos...
because of various peculiarities in their infraciliature. More recent schemes reverse this move, and some molecular studies suggest they may be paraphyletic to the stichotrichs as currently defined.