Gut epithelium of the Highly Toxic Ribbon Worm Cephalothrix cf. simula (Palaeonemertea, Nemertea) Contains Tetrodotoxin-Positive Bacterial Endosymbionts

Magarlamov, Timur Yu.; Malykin, Grigorii V.

doi:10.3390/toxins18030152

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Gut epithelium of the Highly Toxic Ribbon Worm Cephalothrix cf. simula (Palaeonemertea, Nemertea) Contains Tetrodotoxin-Positive Bacterial Endosymbionts

by

Timur Yu. Magarlamov

^*

and

Grigorii V. Malykin

A.V. Zhirmunsky National Scientific Center of Marine Biology, Far Eastern Branch, Russian Academy of Sciences, 690041 Vladivostok, Russia

^*

Author to whom correspondence should be addressed.

Toxins 2026, 18(3), 152; https://doi.org/10.3390/toxins18030152

Submission received: 11 February 2026 / Revised: 20 March 2026 / Accepted: 20 March 2026 / Published: 23 March 2026

(This article belongs to the Section Marine and Freshwater Toxins)

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Abstract

Tetrodotoxin (TTX), widely known as pufferfish venom, is a low-molecular-weight guanidinium neurotoxin. It can accumulate to extremely high concentrations in certain animals, including pufferfish, blue-ringed octopuses, flatworms, and nemerteans. However, the origin of TTX and the mechanisms that enable such extreme accumulation in these animals remain poorly understood. In this study, using confocal laser scanning microscopy combined with electron immunocytochemistry and ultrastructural analysis, we demonstrate the presence of TTX-positive bacteria associated with specialized cellular structures—type II phagosomes of gut enterocytes—in the highly toxic nemertean Cephalothrix cf. simula. We hypothesize that TTX production in C. cf. simula results from interactions between the nemertean host and its endosymbionts. These findings clarify the origin and accumulation of the toxin in nemerteans and have broader implications for other TTX-bearing species.

Keywords: endosymbionts; symbiosome; TTX; tetrodotoxin-producing bacteria; ribbon worm; Cephalothrix simula

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MDPI and ACS Style

Magarlamov, T.Y.; Malykin, G.V. Gut epithelium of the Highly Toxic Ribbon Worm Cephalothrix cf. simula (Palaeonemertea, Nemertea) Contains Tetrodotoxin-Positive Bacterial Endosymbionts. Toxins 2026, 18, 152. https://doi.org/10.3390/toxins18030152

AMA Style

Magarlamov TY, Malykin GV. Gut epithelium of the Highly Toxic Ribbon Worm Cephalothrix cf. simula (Palaeonemertea, Nemertea) Contains Tetrodotoxin-Positive Bacterial Endosymbionts. Toxins. 2026; 18(3):152. https://doi.org/10.3390/toxins18030152

Chicago/Turabian Style

Magarlamov, Timur Yu., and Grigorii V. Malykin. 2026. "Gut epithelium of the Highly Toxic Ribbon Worm Cephalothrix cf. simula (Palaeonemertea, Nemertea) Contains Tetrodotoxin-Positive Bacterial Endosymbionts" Toxins 18, no. 3: 152. https://doi.org/10.3390/toxins18030152

APA Style

Magarlamov, T. Y., & Malykin, G. V. (2026). Gut epithelium of the Highly Toxic Ribbon Worm Cephalothrix cf. simula (Palaeonemertea, Nemertea) Contains Tetrodotoxin-Positive Bacterial Endosymbionts. Toxins, 18(3), 152. https://doi.org/10.3390/toxins18030152

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Gut epithelium of the Highly Toxic Ribbon Worm Cephalothrix cf. simula (Palaeonemertea, Nemertea) Contains Tetrodotoxin-Positive Bacterial Endosymbionts

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