Oyster mushroom is an example of predator fungi that attacks

The correct option is Roundworms.

Step-by-Step Explanation:

1. Nutritional Needs in Nutrient-Poor Environments:
Oyster mushrooms (scientific name: Pleurotus ostreatus) typically grow on decaying wood. While wood provides an abundant source of carbon, it is extremely deficient in nitrogen, which is a vital element required for synthesizing proteins and nucleic acids.

2. Carnivorous Adaptation:
To overcome this nitrogen limitation, the oyster mushroom has evolved a predatory (carnivorous) lifestyle. It preys on microscopic, nitrogen-rich soil organisms called nematodes, which are commonly known as roundworms.

3. Mechanism of Attack:
- Toxin Release: The mycelium (the vegetative network of fungal threads) of the oyster mushroom develops specialized secretory structures containing tiny droplets of toxin.
- Paralysis: When a roundworm comes into contact with these droplets, the potent toxin is released, causing rapid calcium influx and paralysis of the worm's sensory cilia and muscles within minutes.
- Invasion and Digestion: Once the roundworm is completely immobilized, the fungal hyphae grow toward the prey, penetrate its cuticle, and colonize its body cavity.
- Nutrient Absorption: The fungus releases digestive enzymes that break down the roundworm's internal tissues, allowing the mushroom to absorb the digested nitrogen-rich contents.

4. Conclusion:
Through this specialized predatory behavior, the oyster mushroom targets and digests roundworms to supplement its dietary nitrogen requirements.