Nemertea is a phylum of nonsegmented worms (supraphylum: Spiralia), also known as ribbon worms. The members of this phylum contain various toxins, including peptide toxins. Here, we provide a transcriptomic analysis of peptide toxins in 14 nemertean species, including Cephalothrix cf. simula, which was sequenced in the current study. The summarized data show that the number of toxin transcripts in the studied nemerteans varied from 12 to 82. The most represented groups of toxins were enzymes and ion channel inhibitors, which, in total, reached a proportion of 72% in some species, and the least represented were pore-forming toxins and neurotoxins, the total proportion of which did not exceed 18%. The study revealed that nemerteans possess a much greater variety of toxins than previously thought and showed that these animals are a promising object for the investigation of venom diversity and evolution, and in the search for new peptide toxins.

Nemertea is a phylum of marine worms whose members bear various toxins, including tetrodotoxin (TTX) and its analogues. Despite the more than 30 years of studying TTXs in nemerteans, many questions regarding their functions and the mechanisms ensuring their accumulation and usage remain unclear. In the nemertean Kulikovia alborostrata, we studied TTX and 5,6,11-trideoxyTTX concentrations in body extracts and in released mucus, as well as various aspects of the TTX-positive-cell excretion system and voltage-gated sodium (Nav1) channel subtype 1 mutations contributing to the toxins’ accumulation. For TTX detection, an immunohistological study with an anti-TTX antibody and HPLC-MS/MS were conducted. For Nav1 mutation searching, PCR amplification with specific primers, followed by Sanger sequencing, was used. The investigation revealed that, in response to an external stimulus, subepidermal TTX-positive cells released secretions actively to the body surface. The post-release toxin recovery in these cells was low for TTX and high for 5,6,11-trideoxyTTX in captivity. According to the data obtained, there is low probability of the targeted usage of TTX as a repellent, and targeted 5,6,11-trideoxyTTX secretion by TTX-bearing nemerteans was suggested as a possibility. The Sanger sequencing revealed identical sequences of the P-loop regions of Nav1 domains I–IV in all 17 studied individuals. Mutations comprising amino acid substitutions, probably contributing to nemertean channel resistance to TTX, were shown.

Nemertea is a phylum of bilaterally symmetrical, coelomate, unsegmented worms, also known as ribbon worms. Most species of the phylum Nemertea are marine predators that contain toxins in the single-celled glands of the proboscis and/or integument. Recent transcriptomic studies have shown that nemerteans from all taxonomic groups possess a wide range of putative protein and peptide toxins, while the proteomic data for these animals are highly limited. In this study, proteotranscriptomic analysis was used to investigate the major protein components of the poison of the nemertean Kulikovia alborostrata. We identified 146 transcripts of putative toxins in the transcriptome of K. alborostrata and five putative toxins among the secreted proteins and peptides of the mucus of the animal. The expression levels of cysteine-rich peptides found in the mucus with similarity to known toxins were evaluated in different parts of the body of the worm by quantitative real-time PCR. The high level of expression of investigated peptides in the integument indicate the protective function of these toxins. Overall, this supports the idea that the mucus of nemerteans is a valuable source of peptide and protein toxins.

Tetrodotoxin (TTX) is an extremely potent neurotoxin, a selective blocker of voltage-gated sodium (NaV) channels, produced by bacteria and accumulated across a wide range of taxa. Several TTX-bearing animals have developed molecular adaptations in their NaV channels that provide TTX resistance, making this toxin one of the factors of molecular evolution. However, the molecular basis of TTX resistance in NaV channels of a significant proportion of tetrodotoxic species remains poorly studied. Nemertea is a phylum of marine worms, comprising both TTX-bearing and non-TTX-bearing species. Here, we analyzed the amino acid sequences of the NaV1 channel regions responsible for TTX binding from 22 species of nemerteans. Substitutions previously characterized as conferring TTX resistance in other taxa were detected in sixteen nemerteans; local clustering was observed within several families. These findings suggest that TTX resistance in nemerteans evolved multiple times independently and may serve as either as an adaptation facilitating TTX accumulation for subsequent use for defense and predation, or as a mechanism allowing consumption of tetrodotoxic prey without toxin accumulation.

The occurrence of Malacobdella grossa in Peter the Great Bay, Sea of Japan has been confirmed by analysis of cytochrome coxidase subunit I (COI) gene fragments. The sequences of four specimens from the Sea of Japan belong to the same haplotype and differ from the sequences of the specimens from the White and North Seas by three to five substitutions. This is the first hoplonemertean species whose trans-Arctic distribution has been proven at a genetic level. The studied Malacobdella japonica specimens from Aniva Bay (Sakhalin Island) belong to the same haplotype as the specimens from Akkeshi Bay and Ibaraki Prefecture, Japan.