A new species of alien land flatworm in the Southern United States.

Specimens of a flat and dark brown land planarian were found in a plant nursery in North Carolina, USA in 2020. On the basis of examination of photographs of the live specimens only, the specimens were considered as belonging to , a species originally from South America, which has now invaded a large part of Europe. Unexpectedly, a molecular analysis revealed that the specimens did not belong to this species, neither to the genus . We then undertook its histological study, which finally confirmed that the species is a member of the genus : the species is herein described as a new species, n. sp. The species has been found in three locations in North Carolina and some infested plants were from Georgia. We reinvestigated specimens collected in Florida in 2015 and found that they also belong to this species. Citizen science observations suggest its presence in other states. Therefore, it is likely that has already invaded a part of south-east USA and that the invasion took place more than ten years ago. The complete 14,909 bp long mitochondrial genome was obtained. The mitogenome is colinear with those of other Geoplanidae and it was possible to find and annotate a tRNA-Thr, which has been reported missing in several geoplanids. shares with other Geoplaninae the presence of alternative start codons in three protein-coding genes of its mitogenome. The availability of this new genome helped us to improve our annotations of the gene, for which an ATT start codon is now suggested. Also, the sequence of the gene raised questions concerning the use of genetic code 9 to translate the protein-coding genes of Geoplanidae, as the whole translated protein would not contain a single methionine residue when using this code. Two maximum likelihood phylogenies were obtained from genomic data. The first one was based on concatenated alignments of the partial , Elongation Factor 1-alpha ( and genes. The second was obtained from a concatenated alignment of the mitochondrial proteins. Both strictly discriminate from and instead associate it with . We note that the nine species currently accepted within can be separated into two groups, one with extrabulbar prostatic apparatus, including the type species , and one with intrabulbar prostatic apparatus, including the new species . This suggests that species of the latter group should be separated from and constitute a new genus. This finding again illustrates the possible emergence of new invasive species in regions naturally devoid of large land planarians, such as North America. thus deserves to be monitored in the USA, although its superficial resemblance to and will complicate the use of photographs obtained from citizen science. Our molecular information provides tools for this monitoring.