Tetrodotoxin (TTX), known as pufferfish toxin, is a potent neurotoxin blocking sodium channels in muscle and nerve tissues. TTX has been detected in various taxa other than pufferfish, including marine polyclad flatworms, suggesting that pufferfish toxin accumulates in fish bodies via food webs. The composition of TTX and its analogs in the flatworm Planocera multitentaculata was identical to those in wild grass puffer Takifugu alboplumbeus. Previously, Planocera sp. from Okinawa Island, Japan, were reported to possess high level of TTX, but no information was available on TTX analogs in this species. Here we identified TTX and analogs in the planocerid flatworm using high-resolution liquid chromatography–mass spectrometry, and compared the composition of TTX and analogs with those of another toxic and non-toxic planocerid species. We show that the composition of TTX and several analogs, such as 5,6,11-trideoxyTTX, dideoxyTTXs, deoxyTTXs, and 11-norTTX-6(S)-ol, of Planocera sp. was identical to those of toxic species, but not to its non-toxic counterpart. The difference in the toxin composition was reflected in the phylogenetic relationship based on the mitochondrial genome sequence. A toxification experiment using predatory fish and egg plates of P. multitentaculata demonstrated that the composition of TTX and analogs in wild T. alboplumbeus juveniles was reproduced in artificially toxified pufferfish. Additionally, feeding on the flatworm egg plates enhanced the signal intensities of all TTX compounds in Chelonodon patoca and that of deoxyTTXs in Yongeichthys criniger.

河豚毒素 (TTX)，也称为河豚毒素，是一种强效神经毒素，可阻断肌肉和神经组织中的钠通道。 TTX 已在河豚以外的多种分类群中检测到，包括海洋多包扁虫，这表明河豚毒素通过食物网在鱼体内积累。扁虫Planocera multitentaculata中的 TTX 及其类似物的成分与野生草河豚Takifugu alboplumbeus中的成分相同。此前，Planocera sp。据报道，来自日本冲绳岛的TTX具有高水平的TTX，但没有关于该物种中TTX类似物的信息。在这里，我们使用高分辨率液相色谱-质谱法鉴定了扁虫中的 TTX 和类似物，并将 TTX 和类似物的成分与其他有毒和无毒扁虫物种的成分进行了比较。我们证明了Planocera sp的TTX 和几种类似物的组成，例如 5,6,11-trideoxyTTX、dideoxyTTXs、deoxyTTXs 和 11-norTTX-6( S )-ol 。与有毒物种相同，但与无毒物种不同。毒素组成的差异反映在基于线粒体基因组序列的系统发育关系中。使用捕食性鱼类和多触河豚卵盘进行的毒性实验表明，野生白铅鲽鱼幼鱼中的 TTX 和类似物的成分在人工中毒的河豚鱼中得到了复制。此外，以扁虫卵盘为食可增强Chelonodon patoca中所有 TTX 化合物的信号强度以及Yongeichthys creniger中脱氧 TTX 的信号强度。