The tiny and strange marine animal that produces unlimited eggs and sperm over its lifetime is called the turritopsis dohrnii, also known as the immortal jellyfish. This small jellyfish is found in the Mediterranean Sea and the waters of Japan. It has a unique ability to revert from its adult form back to its polyp stage, essentially achieving biological immortality.

Here's how the turritopsis dohrnii accomplishes this remarkable feat:

1. Life Cycle: The turritopsis dohrnii starts its life as a polyp, a small, sedentary stage that attaches to surfaces on the seafloor.

2. Asexual Reproduction: As a polyp, the turritopsis can reproduce asexually by budding. This means it produces genetically identical copies of itself, essentially creating clones.

3. Transformation: Under certain environmental conditions, the polyp can transform into a medusa, which is the adult jellyfish form. This transformation involves significant changes in the animal's structure and physiology.

4. Sexual Reproduction: Once the turritopsis reaches the medusa stage, it becomes sexually mature and can reproduce sexually by releasing eggs and sperm into the water. Fertilization occurs when an egg and sperm meet, forming a new polyp.

5. Reversion: Remarkably, after sexual reproduction and reaching adulthood, the turritopsis dohrnii can revert back to its polyp stage. This process is known as transdifferentiation, where the specialized cells of the adult jellyfish regress and redifferentiate into the simpler cells of the polyp.

6. Repeat Cycle: The turritopsis can repeat the cycle of transforming from a polyp to a medusa and back to a polyp indefinitely. This means it can potentially live forever, continuously reproducing and rejuvenating itself.

It's important to note that while the turritopsis dohrnii is considered biologically immortal, it can still be affected by predators and environmental factors. Additionally, while it has been referred to as "immortal," it hasn't been alive forever, and its lifespan is still being studied.

The turritopsis dohrnii's unique ability to revert to a polyp stage, which sets it apart from other jellyfish species, has fascinated scientists and has implications for our understanding of aging, regeneration, and cellular reprogramming. Studying this tiny marine creature could potentially shed light on new strategies for tissue repair and regeneration in humans.