Ultrastructural features of Allantosoma intestinalis, a Suctorian ciliate isolated from the large intestine of the horse.

This research studied Allantosoma intestinalis, a suctorian ciliate found in the intestine of horses, using light and electron optical methods, and detailed its ultrastructural features, while comparing it with other suctorian genera.

Allantosoma intestinalis Description

• Allantosoma intestinalis is a suctorian ciliate, a type of protozoan that uses membrane-bound tentacles to feed. It is described as small and sausage-shaped.
• The organism hosts between one to fourteen tentacles located at each extremity or end of its body.
• In a cross-sectional view, the axoneme (the core of the tentacle that is primarily responsible for its movement) has two rows of microtubules in a daisy-like configuration.
• The haptocysts, which are either embedded in the tentacle shaft, pressed against the plasma membrane on the knob of the tentacle, or in the cell body, have a bottle-like shape with noticeable striations around their middle section. The Haptocysts are part of the feeding apparatus in suctorians.

Layer and Structure of Cells

• These cells are encased in three distinct membranes: the outer plasma membrane, an outer alveolar membrane and an inner alveolar membrane.
• There is a thin layer of epiplasm beneath the inner alveolar membrane and a single line of microtubules is found below the epiplasm, the gel-like layer beneath the cell membrane.
• Microtubules beneath the skin are aligned parallel to each other to form a structure similar to a corset wrapped around the cell along its long axis which is not a usual feature of suctorians.

Unidentified Structures and Observations

• A collection of 15 tiny kinetosomes, each 180 millimeters long and lacking cilia, were discovered beneath the cortex, the outer layer of the cell.
• The function of these so-called “prokinetosomes” is not yet known.
• Rather than observing a ciliated “swarmer” (a free-swimming stage of tentacled suctorians), only the nonciliated adult was observed in this study, adding to the organism’s unique traits among its Suctorian peers.

The characteristics of Allantosoma have been compared throughout this study with those of other genera in the Suctoria group, with key differences and unique features noted. The structural detail provided in this study contributes to our growing understanding of ciliate biology.