The twelfth essay in the series "Creators" is dedicated to Pavel Semyonovich Galtsov, an outstanding marine biologist who changed the entire oyster industry in America and became the founder of mollusc biology. Together with RASA (Russian-American Science Association) T-invariant continues publishing a series of biographical essays "Creators" about people from the Russian Empire who made a significant contribution to world science and technology, about those to whom we owe our new reality.