Morphological and ontogenetic characteristics of Eustigmaeus pinnatus (Kuznetsov) (Trombidiformes: Stigmaeidae)

Abstract – The morphology and ontogeny of Eustigmaeus pinnatus (Kuznetsov) (Trombidiformes: Stigmaeidae) are described based on specimens collected from soil and litter in Türkiye. All active developmental stages, including larva, protonymph, deutonymph, tritonymph and adults, are examined in detail. The tritonymphal stage, which has rarely been reported in the genus, is documented and characterized. Diagnostic morphological features of each stage are provided, with particular emphasis on the development of idiosomal shields, coxisternal organization, and leg and gnathosomal setation, as well as aggenital configuration. Ontogenetic changes in setation are analysed, and their taxonomic significance is discussed. Comparative assessments of E. pinnatus with E. jiangxiensis Hu, Chen & Huang and E. turcicus Doğan & Ayyıldız are also presented. The results contribute to a better understanding of character development within the genus. 2026 Systematic and Applied Acarology Society