Phylum CILIOPHORA Doflein, 1901
Subphylum POSTCILIODESMATOPHORA Gerassimova & Seravin, 1976
Class HETEROTRICHEA Stein, 1859
Order Heterotrichida Stein, 1859
Stentor can be found in ponds, lakes, and slow moving streams. They may be sessile or free-swimming. The sessile form adheres tightly to the substrate using a mucoid substance secreted at the posterior end of the cell.
Stentor can contract rapidly. This is caused by more-or-less straight and thick, longitudinal fibres called myonemes that run beside the somatic or body kineties. These fibres originate near the peristome and terminate in the posterior holdfast. Stentor elongates its body again by sliding the microtubular ribbons of its postciliodesmata along each other.
Stentor are omnivorous. They feed on small rotifers, algal cells, bacteria, flagellates, and other ciliates, such as Tetrahymena. Some Stentor species, such as Stentor polymorphus, harbor green algal symbionts of the genus Chlorella. This mixotrophic species is able to feed on prey and also benefit from the products of photosynthesis manufactured by its Chlorella.
SOMATIC / ORAL STRUCTURE
Members of the family Stentoridae are between 1-3 mm in length. When expanded, the anterior end of Stentor forms a flattened or slightly convex peristomal disk with a conspicuous adoral zone of membranelles (AZM) encircling its perimeter. The AZM is used for feeding and locomotion. The body tapers below the oral disk and terminates in a posterior holdfast with which this ciliate may attach itself to the substrate. In this expanded state, Stentor looks like a trumpet. This is how it gets its name, which derives from the Greek word Stentor, who was a herald with a voice as loud as fifty men.
The whole body surface of Stentor is covered with cilia, which are arranged in rows that correspond with striations on the cell body. The striations are caused by alternating bands of pigmented and non-pigmented ectoplasm. The pigment, called stentorin, enables Stentor to be sensitive and responsive to light.
The AZM encircles the perimeter of the peristome and winds into an enclosed funnel-shaped part of the oral cavity that leads to the cytostome. In feeding, AZM cilia create currents that drive particles toward the cytostome, which is located at the base of the funnel-shaped region. Stentor can reject particles if it finds them "distasteful".
DIVISION MORPHOGENESIS / NUCLEI AND SEXUALITY
The macronucleus consists of a string of elliptical nodes held together by cytoplasmic bridges-a moniliform arrangement. Some species of Stentor can have over 40 micronuclei.
Stentor reproduce through binary fission. Prior to division, the macronuclear nodes fuse into an ovoid form. Division begins with the appearance of a field of kinetosomes located between the peristome and the holdfast, in the so-called region of stripe contrast. The kinetosomes, which arise from replication of kinetosomes in the ventral kineties, develop into an oral primordium that eventually forms the oral apparatus of the opisthe or daughter cell. The proter or parental cell retains its oral apparatus, although some remodelling of it may occur during cell division.
Cytokinesis or cell division occurs by formation of an oblique cleavage line, separating the opisthe's oral primordium into the posterior half. During cytokinesis, the ovoid macronucleus becomes more elongate as microtubule bundles form outside the macronuclear envelope, the so-called extramacronuclear microtubules. Once the macronucleus has separated into two and the cells have also separated, the macronuclear nodes begin to form again.
Like other ciliates, Stentor undergo sex through the process of conjugation. Two cells fuse near their anterior ends and then exchange gametic micronuclei.