Anomalous segmentation of Diphyllobothrium nihonkaiense.

An anomalous tapeworm with abnormal segmentation was obtained from a 6-year-old boy in Japan. The tapeworm consisted of proglottids with slanted anterior and posterior margins of proglottids and 4-6 sets of reproductive organs arranged between the margins. The morphology of the tapeworm did not correspond to any of the described cestodes. However, molecular identification based on nuclear and mitochondrial genes clearly showed the tapeworm was Diphyllobothrium nihonkaiense.