Antennarius euglyphus represents an early record of the frogfish lineage, a group of highly specialised anglerfishes. Living frogfishes are slow-moving ambush predators that use a modified dorsal-fin spine as a lure, but A. euglyphus is known from otoliths rather than a complete skeleton. Its placement therefore indicates that antennariids were present by the early Eocene, while the detailed body form and behaviour of this particular species remain inferred from its family relationship.

The fossil record of A. euglyphus is consequently very different from that of the large three-dimensional London Clay skulls. The species is recognised through the morphology of the sagittal otolith, an internal ear stone whose shape and sulcus preserve taxonomically useful characters even when the rest of the fish is absent.