Rediscovery after Almost 120 Years: Morphological and genetic evidence supporting the validity of daphnia mitsukuri (Crustacea: Cladocera)

We examined the morphology of Daphnia individuals maintained in our laboratory for several years, originally collected in Lake Inbanuma, Chiba, Japan. We determined partial sequences of the mitochondrial cytochrome c oxidase subunit I and 12S rRNA genes from specimens in the cultured material. These animals are morphologically similar to D. obtusa Kurz, 1874, but genetically distinct from this species. Our detailed observation shows that the morphological characteristics in the female and male individuals of our material are highly congruent with those of D. mitsukuri Ishikawa, 1896, which has not been identified positively for more than 120 years since its original description, with its taxonomic identity having been questioned for almost 90 years. Based on our morphological and genetic data, we conclude that D. mitsukuri should be regarded as a taxonomically valid species. A search among public DNA sequence databases suggests D. mitsukuri is also distributed in China, although these Chinese sequences have been labeled as 'Daphnia pulex', representing misidentification.