Citrus nematodes, Tylenchulus semipenetrans, parasitizing a citrus root. The second-stage larvae initially feed on root hairs. The larvae then penetrate into the feeder roots, molt three times, and establish a permanent feeding site (nurse cells) inside the root cortex. The swollen rear end of the mature female remains outside the root.

Illustration from Integrated Pest Management for Citrus, 1st edition. UC ANR Publication 3303.