Acinetospora crinita is a filamentous brown alga in the order Ectocarpales, forming delicate, branching thalli on rocky intertidal substrates and on larger seaweeds along temperate coastlines. Its life cycle alternates between morphologically similar gametophyte and sporophyte generations. As an epiphytic and epilithic alga, it contributes to the diversity of intertidal algal communities.