Postlarval Development of the Cretaceous Hemiaster akkaptschigensis Schmidt, 1962 and the Extant Holanthus expergitus (Lovén, 1874), and Their Significance for the Systematics of Hemiasteridae (Echinoidea, Spatangoida)

Based on a detailed study of morphology, postlarval development and morphometric analysis, the age-related variability of the species Hemiaster akkaptschigensis and Holanthus expergitus is shown. Changes in qualitative and quantitative aspects during the postlarval development of these species are traced. Differences and similarities in the nature of changes in characters and morphology have been identified, revealing the degree of relationship between these species, refining their taxonomy and supporting their re-assignment to different genera.