Herein we report on the most abundant and diverse fauna of Palaeozoic crinoids and blastoids collected from Mongolia to date. The fauna is from the Late Devonian (Famennian) Samnuuruul Formation in western Mongolia. The fauna consists of two genera of blastoids and twelve genera of crinoids—four genera of camerates, three genera of flexibles, one disparid genus, and four genera of cladids. The crinoids and blastoids were living on an active island arc complex in the Central Asian Orogenic Belt (CAOB) in a high physical stress environment with frequent and often voluminous pyroclastic eruptions. The Mongolian fauna is similar to coeval faunas collected from the Hongguleleng Formation in western China and supports the hypothesis that the CAOB was a biodiversity hotspot for Famennian echinoderms and a precursor to the very successful echinoderm communities that dominated Mississippian shallow-marine ecosystems globally. Three new taxa are described. Mongoliacrinus minjini, new genus and species, is the oldest member of the Acrocrinidae, previously known from the Mississippian and Pennsylvanian and the first occurrence of the family outside North America. Eutaxocrinus ariunai and Eutaxocrinus sersmaai are new species of the flexible crinoid Eutaxocrinus, a genus with a widespread distribution during the Early and Middle Devonian, which survived into the Lower Mississippian. It is restricted to the CAOB in the Late Devonian.