Binary Fission > Longitudinal Binary Fission

When a unicellular organism divides along the longitudinal (vertical) axis, it is called longitudinal binary fission.

or

Longitudinal binary fission is an asexual reproduction process where the plane of division passes along the longitudinal (vertical) axis of the animal, splitting it into two parts.

Example: Euglena

Euglena (Protozoa)

• Preparation: During fission, the organism suspends its locomotory activities, and the flagellum is sometimes withdrawn.
• Division of Organelles: The division process begins with the splitting of the blepharoplast.
• Nuclear Division: Following the blepharoplast, the nucleus undergoes eumitotic division. Eumitosis is a specific type of mitosis in which the nuclear membrane completely dissolves, meaning there is temporarily no distinction between the cytoplasm and the nucleoplasm.
• Cytokinesis (Cleavage): A cleavage furrow (longitudinal furrow) originates from the reservoir at the anterior end. This furrow proceeds longitudinally down the body to gradually divide the animal into two.
• Formation of Daughter Cells & Regeneration: The deep furrow eventually separates the organism into two independent daughter euglenae. Any lost parts in the two new daughter cells are regenerated immediately after the division is complete.

Euglena: stages in longitudinal binary fission

• A unicellular organism divides along its longitudinal (vertical) axis, splitting into two daughter cells - an asexual reproduction process, as seen in Euglena.
• The cell first suspends locomotion (flagellum sometimes withdrawn), then the blepharoplast splits, followed by eumitotic nuclear division where the nuclear membrane fully dissolves.
• A longitudinal cleavage furrow begins at the reservoir on the anterior end and proceeds down the body, gradually dividing the cell into two.
• The furrow deepens until two independent daughter euglenae are formed, with any lost parts regenerated immediately after division.