Delimiting species in the Phacus longicauda complex (Euglenida) through morphological and molecular analyses

Area of Science:

• Protistology
• Eukaryotic Microbiology
• Algology

Background:

• Phacus longicauda is the type species of Phacus, yet its identification is difficult due to over 30 morphologically similar taxa.
• Lack of clear diagnostic features hinders accurate species delimitation within this common group of autotrophic euglenids.

Purpose of the Study:

• To delimit species within the Phacus longicauda complex using environmental sampling and molecular data.
• To provide accurate taxonomic descriptions and designate epitypes for verified species.

Main Methods:

• Environmental sampling and whole genome amplification from small cell numbers (20-30) without laboratory cultures.
• Morphological and molecular phylogenetic analyses based on nuclear small subunit ribosomal DNA (nSSU rDNA) variation.
• Isolation and analysis of 36 strains from environmental samples, primarily from Poland.

Main Results:

• Four species were distinguished within the Phacus longicauda complex: P. longicauda, P. circumflexus, P. helikoides, and P. tortus.
• Two new species, Phacus cristatus sp. nov. and Phacus crassus sp. nov., were described.
• Two species, Phacus cordata and Phacus rotunda, had their taxonomic ranks changed (comb. nov.).
• Diagnostic descriptions were amended, and epitypes were designated for all verified species.

Conclusions:

• This study successfully resolved the taxonomic uncertainty within the Phacus longicauda complex.
• The integration of molecular and morphological data provides a robust framework for identifying and classifying these common euglenids.
• The description of new species and revision of existing ones contributes significantly to the understanding of Phacus diversity.