thumb|right|The head of a mantis showing the black pseudopupil in its compound eyes thumb|right|The eye of a mantis shrimp has three regions, each with its own pseudopupil.
thumb|right|The head of a mantis showing the black pseudopupil in its compound eyes thumb|right|The eye of a mantis shrimp has three regions, each with its own pseudopupil.
In the compound eye of invertebrates such as insects and crustaceans, the pseudopupil appears as a dark spot which moves across the eye as the animal is rotated. This occurs because the ommatidia that one observes "head-on" (along their optical axes) absorb the incident light, while those to one side reflect it. The pseudopupil therefore reveals which ommatidia are aligned with the axis along which the observer is viewing.
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).