Molecular phylogeny of Chromadorea supports genus reclassification of Desmodorida and Microlaimida with the description of two new species from the Yellow Sea, China

Phylogenetic relationships within the marine Chromadorea are complex, and the taxonomic positions at the family and genus levels remain flexible due to discrepancies between morphological and molecular evidence. During our taxonomic study in the Yellow Sea, two species, Pseudochromadora crispata sp. nov. and Microlaimus parakoranus sp. nov., are described. Pseudochromadora crispata sp. nov. is characterized by a short body, a coarsely annulated cuticle with lateral alae, a unispiral amphidial fovea, slightly curved spicules, a gubernaculum plate shaped with a cuticularized lateral piece, four ventral precloacal copulatory thorns, and one pair of postcloacal thorns.

Microlaimus parakoranus sp. nov. is characterized by a finely striated cuticle, short cephalic setae, a cryptocircular amphidial fovea, the absence of somatic setae, slightly curved spicules with swollen proximal ends, a heavily cuticularized gubernaculum, and a conical tail with a slightly cylindrical distal end. Phylogenetic analysis within Chromadorea indicates that the genera Prodesmodora and Molgolaimus should be transferred to Chromadorida, the genera Nudora and Monoposthia should be removed from Microlaimida based on morphological and molecular evidence, and Onepunema should be kept in Desmodoridae despite its anomalous phylogenetic position.