New insights into non-marine monothalamids (Rhizaria, Foraminifera): The rediscovery of Limnogromia saxicola (Penard, 1905) and description of four new species

Non-marine foraminifera remain among the least explored groups within the Rhizaria, despite their ecological and evolutionary significance. We report the rediscovery of the agglutinated monothalamid Limnogromia saxicola (Penard, 1905) and provide the first integrative morphological and molecular characterization of this species since its original description. In addition, we describe four new organic-walled monothalamids based on morphological and molecular data: Claparedellus arenivagus sp. nov., C. dunicola sp. nov., Perseforaminifer crypticus gen. et sp. nov., and Edaphoallogromia bettighoferi sp. nov. Morphological differentiation is challenging due to limited diagnostic characters and intraspecific variability, although nuclear architecture and birefringent cytoplasmic crystals provide useful markers. Limnogromia saxicola and P. crypticus include environmental sequences that are nearly identical to those obtained from individually extracted specimens. This is the first time that environmental sequences can be confidently linked to defined species. Additionally, brief descriptions and illustrations are provided for seven undetermined monothalamous morphotypes for which no sequences could be obtained. Our findings expand the known diversity, ecological range, and cryptic complexity of freshwater monothalamids. This study underscores the importance of integrating morphological, molecular, and ecological data to resolve taxonomy, detect cryptic diversity, and better understand the evolutionary history of non-marine monothalamids.