The organism you're describing is likely a Giardia lamblia, also known as Giardia intestinalis.

Here's why:

* Long cell: Giardia are single-celled organisms (protozoa) with a distinctive elongated, pear-shaped body.

* Pouch containing two flagella: At the anterior (front) end of the cell, Giardia have a ventral sucking disc and a pear-shaped structure called a ventral groove that houses two flagella.

Giardia is a parasitic protozoan that can cause giardiasis, a common intestinal infection.