Protistiary - Orientation: What is the Front?

What is the front ?
Not all protistan cells have a front. But when people talk of front (or anterior), they will probably be guided by one ofthese criteria: - The front is the part of the cell that leads the way when the cell is moving (see Amoeba, Anisonema, Actinomonas, Paramecium, Lacrymaria, Didinium) - If there is a single flagellum or a few flagella inserted at a pole, the front is that pole (see Actinomonas, Crinolina, Telonema) - If there is a polar mouth, the front is the part of the cell that has the mouth (see Lacrymaria, Didinium, Telonema) These criteria are not consistent - hairy flagella (of stramenopiles) at the front of the cell will draw a cell forward, so in this case anterior will be the same by the first two criteria. In the case of a cell that has a smooth flagellum, waves that pass from base to tip will push the cell forward and the flagella will trail behind the cell. In such cells, the location of the flagellum tends to be the feature that determines the front of the cell, and the cell is said to swim backwards. All of the following organisms are shown with the anterior to the top of the page, and this is a useful convention to adopt where possible.
	Amoeba, the pseudopodia are rounded at their anterior ends. The crumpled uroid defines the back of the cell.	Anisonema, a euglenid. One long flagellum trails behind the moving cell, and one projects from the front of the moving cell.	Actinomonas, a stramenopile, has a single emergent flagellum at the anterior end. When the cell swims, the presence of hairs ensures that the cell is drawn forward.	Crinolina, an acanthoecid choanoflagellate. The flagellum inserts at one pole of the cell. If the choanoflagellate cells are able to swim freely, then they swim with the posterior end of the cell pointing forward and the flagellum pushing from behind the moving cell. In this case, the insertion of the flagellum determines anterior.
	Paramecium, a ciliate. The more rounded end is the leading end when the cell is swimming, and the tapered posterior end also has a tuft of slightly longer caudal cilia.	Lacrymaria is a predatory ciliate, in which the mouth is at the end of the extensible 'neck'. The location of the mouth defines anterior.	Didinium is a predatory ciliate, it swims with the conical projection progressing forward and this is also the mouth - anterior is then defined by both criteria.	Telonema is a predatory flagellate. The two flagella insert into a small depression. When the cell swims, the flagella are directed behind the cell, so in this case location of flagella and direction of movement give different indicators of what is anterior. Food is ingested near the point of flagellar insertion.

Protistiary home page top of electron microscopy exercise

What is the front ?

Not all protistan cells have a front. But when people talk of front (or anterior), they will probably be guided by one ofthese criteria:

- The front is the part of the cell that leads the way when the cell is moving (see Amoeba, Anisonema, Actinomonas, Paramecium, Lacrymaria, Didinium)

- If there is a single flagellum or a few flagella inserted at a pole, the front is that pole (see Actinomonas, Crinolina, Telonema)

- If there is a polar mouth, the front is the part of the cell that has the mouth (see Lacrymaria, Didinium, Telonema)

These criteria are not consistent - hairy flagella (of stramenopiles) at the front of the cell will draw a cell forward, so in this case anterior will be the same by the first two criteria. In the case of a cell that has a smooth flagellum, waves that pass from base to tip will push the cell forward and the flagella will trail behind the cell. In such cells, the location of the flagellum tends to be the feature that determines the front of the cell, and the cell is said to swim backwards.

All of the following organisms are shown with the anterior to the top of the page, and this is a useful convention to adopt where possible.

Amoeba, the pseudopodia are rounded at their anterior ends. The crumpled uroid defines the back of the cell.

Anisonema, a euglenid. One long flagellum trails behind the moving cell, and one projects from the front of the moving cell.

Actinomonas, a stramenopile, has a single emergent flagellum at the anterior end. When the cell swims, the presence of hairs ensures that the cell is drawn forward.

Crinolina, an acanthoecid choanoflagellate. The flagellum inserts at one pole of the cell. If the choanoflagellate cells are able to swim freely, then they swim with the posterior end of the cell pointing forward and the flagellum pushing from behind the moving cell. In this case, the insertion of the flagellum determines anterior.

Paramecium, a ciliate. The more rounded end is the leading end when the cell is swimming, and the tapered posterior end also has a tuft of slightly longer caudal cilia.

Lacrymaria is a predatory ciliate, in which the mouth is at the end of the extensible 'neck'. The location of the mouth defines anterior.

Didinium is a predatory ciliate, it swims with the conical projection progressing forward and this is also the mouth - anterior is then defined by both criteria.

Telonema is a predatory flagellate. The two flagella insert into a small depression. When the cell swims, the flagella are directed behind the cell, so in this case location of flagella and direction of movement give different indicators of what is anterior. Food is ingested near the point of flagellar insertion.

Protistiary home page top of electron microscopy exercise