A flatworm on the move

Photograph by Makiri Sei

Platydemus manokwari, the New Guinea flatworm, is a highly invasive species, already reported in several regions of the Pacific area, and as well as in France. This is the only land planarian that made it on the list of the '100 worst invasive alien species'.  It feeds on land snails and thus represents a danger to endemic species. Very flat, it is about 50 mm long and 5 mm wide. Although it lives on the ground, it is able to climb trees to follow and consume native snails.

A new study published in PeerJ reports on new occurrences of Platydemus manokwari in several additional countries and territories: Singapore, New Caledonia (including mainland and two of the Loyalty Islands), an additional island in French Polynesia, Wallis and Futuna (from two of the islands, Uvea and Futuna), the Solomon Islands, Puerto Rico and Florida, USA - the latter being the first records on the American continent.

Specimens of the flatworm from various territories were identified by their characteristic appearance, a histological study and DNA Barcoding. 

Sequences of COI comprised two haplotypes, “Australian” (with a minor variation on a single nucleotide in a single specimen among 13) and “World” (France, New Caledonia, Singapore, Tahiti, Florida, Puerto Rico; all identical in 19 specimens). The two haplotypes were found together in the same locality only in the Solomon Islands. The difference of 4.8% between the two variants of P. manokwari found here could be either considered as relatively high intraspecific variation, or as evidence for the presence of two different species. In view of the limited morphological and anatomical differences found between specimens with known haplotypes, and the small size of our sample, we provisionally conclude that a single species, Platydemus manokwari, is involved.

The country of origin of Platydemus manokwari is New Guinea, and Australia and the Solomon Islands are the countries closest to New Guinea from which samples were used. This suggest that two haplotypes exist in the area of origin of the species, but that only one of those (the 'World haplotype') has, through human agency, been widely dispersed. 

The record in Florida is of particular concern because it is in mainland America. Until now, infested territories were mostly islands, and a spread from island to island is usually limited. However, the flatworms now established in Florida will not be subject to these limitations. In addition to their natural spread, flatworms can easily be passively spread through infested plants, plant parts and soil. Therefore, Platydemus manokwari could potentially spread from Florida throughout the U.S., and this should be considered a significant threat to North America.