Watch List notes:

MYSIA, Kyzikos. Circa 600-550 BC. Fourrée Hemihekte – Twelfth Stater (7mm, 0.85 g). Two tunnies, one above the other, facing opposite directions / Incuse square punch. Von Fritze –; SNG France –; Hurter & Liewald III 35.4 (also a fourrée). VF. Rare.

Although there is no visible evidence that this coin is fourrée, there can be no other explanation for its low weight.