Molecular phylogenetics facilitates the first historical biogeographic analysis of the hammerhead worms (Platyhelminthes: Tricladida: Bipaliinae), with the description of twelve new species and two new genera.

The hammerhead worms constitute a land planarian subfamily (Platyhelminthes: Tricladida: Bipaliinae) that is popular among natural historians as well as citizen scientists due to their characteristic semi-lunar-shaped head, the striking colours of many species, and the worldwide presence of introduced species, which has raised much concern about their putative impact on the receiving ecosystems. Despite such current awareness, the majority of Bipaliinae species was described before the second half of the 20th century. Over the past few decades, description of new species has been rather scarce.

New molecular sequences for two genera of marine planarians facilitate determination of their position in the phylogenetic tree, with new records for two species (Platyhelminthes, Tricladida, Maricola).

For the first time, molecular sequences of the 18S ribosomal DNA were generated for representatives of the genera Sluys & Ball, 1989 and Sluys, 1989 of the suborder of the marine triclads, or Maricola, by analyzing the species (Hallez, 1906) and (Ijima & Kaburaki, 1916). On the basis of this molecular data the phylogenetic position of these two genera in the phylogenetic tree of the Maricola was determined and compared with their position in the phylogeny based on the analysis of anatomical features. New records for these two species are documented and their taxonomic status is determined on the basis of histological studies.