SSU rRNA reveals a sequential increase in shell complexity among the euglyphid testate amoebae (Rhizaria: Euglyphida)

Area of Science:

• Protistology
• Molecular Phylogenetics
• Evolutionary Biology

Background:

• Existing molecular phylogenies for Euglyphida show discrepancies with morphological classifications.
• The phylogenetic positions of several key genera within Euglyphida remain unresolved, hindering a comprehensive understanding of their evolutionary history.

Purpose of the Study:

• To resolve phylogenetic uncertainties within the order Euglyphida.
• To elucidate the evolutionary relationships among major euglyphid genera and families.
• To investigate the evolutionary pathways driving morphological diversity in testate amoebae.

Main Methods:

• Acquisition and analysis of new small subunit ribosomal RNA (SSU rRNA) gene sequences from five genera and seven species of filose testate amoebae.
• Phylogenetic reconstruction using SSU rRNA data to infer evolutionary relationships.

Main Results:

• The genera Assulina and Placocista form a basal clade within Euglyphida, branching prior to the Trinematidae and Euglypha subclade.
• The family Trinematidae is identified as the sister group to the genus Euglypha.
• Three newly sequenced species of Euglypha form a distinct clade within the genus Euglypha.
• The proposed new family Assulinidae accommodates Assulina and Placocista, while Euglypha and Scutiglypha are tentatively placed in the new family Euglyphidae.

Conclusions:

• The study establishes a robust molecular phylogeny for Euglyphida, necessitating revisions to existing taxonomic classifications.
• The proposed new families Assulinidae and Euglyphidae reflect the inferred evolutionary relationships based on SSU rRNA data.
• Evolutionary trends indicate a progression towards increased shell morphological complexity, including changes in aperture position and scale specialization.