The diet and distribution of Pentacoelum kazukolinda (Kawakatsu & Mitchell, 1984), a maricolan planarian with a freshwater ecology

Among the marine triclads or Maricola, the genus Pentacoelum represents one of the few exceptions in that species occur in brackish water or in freshwater. We examined specimens of a maricolan triclad that externally looked remarkably similar to the continental Spanish representatives of freshwater Pentacoelum hispaniense, albeit that these new samples came from habitats in Germany, the Netherlands, Mallorca and Japan. Comprehensive comparative morphological studies revealed that the animals from these populations are identical to a species described earlier from Hawaii, viz. Oahuhawaiiana kazukolinda Kawakatsu & Mitchell, 1984. It is argued that the species now should be called Pentacoelum kazukolinda (Kawakatsu & Mitchell, 1984) comb. nov. Remarkably, Dutch and German specimens of P. kazukolinda almost completely lack any signs of the presence of the lateral gonopore system, being the defining feature of their taxonomic family, the Bdellouridae. The reason for this reduction or even complete absence of this structure remains obscure. Nonetheless, morphological similarities and 18S rDNA sequences strongly suggest that all animals belong to the same species. Analyses of the mitochondrial gene sequences Cox1 and 16SrDNA of the gut content of P. kazukolinda revealed that the flatworm has a preference for different species of gastropods, while in one population annelids were detected. Our study suggests that gastropods may form the food refuge of P. kazukolinda. Circumstantial evidence suggests that the worldwide distribution of P. kazukolinda may result from human‐mediated transport of the aroid Colocasia esculenta and/or the introduced snail Potamopyrgus antipodarum. The use of P. antipodarum as a food resource may have facilitated the spread and establishment of new populations of P. kazukolinda.