New branch on the tree of life of Gastrotricha: establishment of a new genus for limno-terrestrial species

Gastrotricha encompass a diversity of free-living micrometazoans typically associated with aquatic or semi-aquatic environments. The discovery of a gastrotrich species in limno-terrestrial habitats challenges existing taxonomic classifications and expands our understanding of their ecological diversity. This study describes Dendroichthydium ibyrapora gen. et sp. nov., a new gastrotrich from epiphytic mosses found in Atlantic rainforest within Serra do Japi biological reserve, and establishes its taxonomic status through morphological and molecular analyses. Morphological characterization was conducted using light microscopy, scanning electron microscopy, and confocal laser scanning microscopy, revealing that D. ibyrapora exhibits distinctive adaptations suited to limno-terrestrial environments, including unique cuticular adaptations and rearrangement of locomotory cilia. Molecular phylogenetics, using 18S and 28S ribosomal DNA sequences, supports the recognition of Dendroichthydium as a new genus, distinctly separated from known genera within Paucitubulatina. Furthermore, we propose reclassifying Chaetonotus (Chaetonotus) silvaticus to Dendroichthydium silvaticus comb. nov. based on shared morphological traits. The establishment of the genus Dendroichthydium reflects the ongoing need to re-evaluate gastrotrich diversity and taxonomy, highlighting the role of underexplored limno-terrestrial habitats in hosting unique life forms. This study underscores the importance of integrating morphology and genetics to improve our understanding of phylogenetics and the evolutionary dynamics of Gastrotricha.