selenocystine
The selenoamino acid selocystine has been found in seagull eggs.
The term "selenocystine" was found in the following pages:
Selenium species are partly converted during their enzymatic extraction from biological samples with protease XIV | EVISA's News
Link database: Selenium and Livestock: Metabolism, Toxicity and Deficiency
Selenium Speciation in Fortified Vegetables | EVISA's News