Seven new species of Tetranemertes Chernyshev, 1992 (Monostilifera, Hoplonemertea, Nemertea) from the Caribbean Sea, western Pacific, and Arabian Sea, and revision of the genus

The marine ribbon worm genus Tetranemertes Chernyshev, 1992 currently includes three species: the type species T.antonina (Quatrefages, 1846) from the Mediterranean Sea, T.rubrolineata (Kirsteuer, 1965) from Madagascar, and T.hermaphroditica (Gibson, 1982) from Australia. Seven new species are described: T.bifrostsp. nov., T.ocelatasp. nov., T.majinbuuisp. nov., and T.pastafariensissp. nov. from the Caribbean Sea (Panamá), and three species, T.unistriatasp. nov., T.paulayisp. nov., and T.arabicasp. nov., from the Indo-West Pacific (Japan and Oman). As a result, an amended morphological diagnosis of the genus is offered. To improve nomenclatural stability, a neotype of Tetranemertesantonina is designated from the Mediterranean. The newly described species, each characterized by features of external appearance and stylet apparatus, as well as by DNA-barcodes, form a well-supported clade with T.antonina on a molecular phylogeny of monostiliferan hoplonemerteans based on partial sequences of COI, 16S rRNA, 18S rRNA, and 28S rRNA. Six of the seven newly described species, as well as T.rubrolineata, possess the unusual character of having a central stylet basis slightly bilobed to deeply forked posteriorly in fully grown individuals, a possible morphological synapomorphy of the genus. In addition, an undescribed species of Tetranemertes is reported from the Eastern Tropical Pacific (Panamá), increasing the total number of known species in the genus to eleven.

Intrabody Tetrodotoxin Distribution and Possible Hypothesis for Its Migration in Ribbon Worms Cephalothrix cf. simula (Palaeonemertea, Nemertea)

Tetrodotoxin (TTX) is a potent neurotoxin found in many marine and terrestrial animals, but only a few species, such as the ribbon worms of the genus Cephalothrix, accumulate it in extremely high concentrations. The intrabody distribution of TTX in highly toxic organisms is of great interest because it helps researchers to understand the pathways by which the toxin migrates, accumulates, and functions in tissues. Using immunohistochemistry with anti-TTX antibodies, the authors of this study investigated the toxin's distribution inside the organs, tissues, and cells of Cephalothrix cf. simula. The cell types of TTX-positive tissues were identified by light microscopy. The main sites of TTX accumulation occurred in the secretory cells of the integuments, the microvilli of the epidermal ciliary cells, cephalic glands, the glandular epithelia of the proboscises, the enterocytes of the digestive systems, and nephridia. Obtained data suggest the toxin migrates from the digestive system through blood vessels to target organs. TTX is excreted from the body through the nephridia and mucus of epidermal cells.

Tetrodotoxins Secretion and Voltage-Gated Sodium Channel Adaptation in the Ribbon Worm Kulikovia alborostrata (Takakura, 1898) (Nemertea)

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.

Genome Size Dynamics in Marine Ribbon Worms (Nemertea, Spiralia)

Nemertea is a phylum consisting of 1300 mostly marine species. Nemertea is distinguished by an eversible muscular proboscis, and most of the species are venomous. Genomic resources for this phylum are scarce despite their value in understanding biodiversity. Here, we present genome size estimates of Nemertea based on flow cytometry and their relationship to different morphological and developmental traits. Ancestral genome size estimations were done across the nemertean phylogeny. The results increase the available genome size estimates for Nemertea three-fold. Our analyses show that Nemertea has a narrow genome size range (0.43-3.89 pg) compared to other phyla in Lophotrochozoa. A relationship between genome size and evolutionary rate, developmental modes, and habitat was found. Trait analyses show that the highest evolutionary rate of genome size is found in upper intertidal, viviparous species with direct development. Despite previous findings, body size in nemerteans was not correlated with genome size. A relatively small genome (1.18 pg) is assumed for the most recent common ancestor of all extant nemerteans. The results provide an important basis for future studies in nemertean genomics, which will be instrumental to understanding the evolution of this enigmatic and often neglected phylum.

The Toxins of Nemertean Worms

Most ribbon worms (phylum: Nemertea) are found in marine environments, where they act as predators and scavengers. They are characterized by an eversible proboscis that isused to hunt for prey and thick mucus covering their skin. Both proboscis and epidermal mucus mediate toxicity to predators and preys. Research into the chemical nature of the substances that render toxicity has not been extensive, but it has nevertheless led to the identification of several compounds of potential medicinal use or for application in biotechnology. This review provides a complete account of the current status of research into nemertean toxins.

Tubulanus tamias sp. nov. (Nemertea: Palaeonemertea) with Two Different Types of Epidermal Eyes

Based on specimens collected subtidally (∼10 m in depth) in Tomioka Bay, Japan, we describe the palaeonemertean Tubulanus tamias sp. nov., which differs from all its congeners in body coloration. In molecular phylogenetic analyses based on partial sequences of the nuclear 18S and 28S rRNA genes and histone H3, as well as the mitochondrial 16S rRNA and cytochrome c oxidase subunit I genes, among selected palaeonemerteans, T. tamias nested with part of the congeners in Tubulanus, while the genus as currently diagnosed appears to be non-monophyletic. Molecular cloning detected polymorphism in 28S rDNA sequences in a single individual of T. tamias, indicating incomplete concerted evolution of multiple copies. Tubulanus tamias is peculiar among tubulanids in having 9-10 pigment-cup eyes in the epidermis on either side of the head anterior to the cerebral sensory organs, and remarkably there are two types of eyes. The anterior 8-9 pairs of eyes, becoming larger from anterior to posterior, are completely embedded in the epidermis and proximally abutting the basement membrane; each pigment cup contains bundle of up to seven, rod-shaped structure that resemble a rhabdomeric photoreceptor cell. In contrast, the posterior-most pair of eyes, larger than most of the anterior ones, have an optical cavity filled with long cilia and opening to the exterior, thus appearing to have ciliary-type photoreceptor cells. The size and arrangement of the eyes indicate that the posterior-most pair of eyes are the remnant of the larval (or juvenile) eyes.

Nemertean toxin genes revealed through transcriptome sequencing

Nemerteans are one of few animal groups that have evolved the ability to utilize toxins for both defense and subduing prey, but little is known about specific nemertean toxins. In particular, no study has identified specific toxin genes even though peptide toxins are known from some nemertean species. Information about toxin genes is needed to better understand evolution of toxins across animals and possibly provide novel targets for pharmaceutical and industrial applications. We sequenced and annotated transcriptomes of two free-living and one commensal nemertean and annotated an additional six publicly available nemertean transcriptomes to identify putative toxin genes. Approximately 63–74% of predicted open reading frames in each transcriptome were annotated with gene names, and all species had similar percentages of transcripts annotated with each higher-level GO term. Every nemertean analyzed possessed genes with high sequence similarities to known animal toxins including those from stonefish, cephalopods, and sea anemones. One toxin-like gene found in all nemerteans analyzed had high sequence similarity to Plancitoxin-1, a DNase II hepatotoxin that may function well at low pH, which suggests that the acidic body walls of some nemerteans could work to enhance the efficacy of protein toxins. The highest number of toxin-like genes found in any one species was seven and the lowest was three. The diversity of toxin-like nemertean genes found here is greater than previously documented, and these animals are likely an ideal system for exploring toxin evolution and industrial applications of toxins.

Highly toxic ribbon worm Cephalothrix simula containing tetrodotoxin in Hiroshima Bay, Hiroshima Prefecture, Japan

In 1998, during a toxicological surveillance of various marine fouling organisms in Hiroshima Bay, Japan, specimens of the ribbon worm, Cephalothrix simula (Nemertea: Palaeonemertea) were found. These ribbon worms contained toxins with extremely strong paralytic activity. The maximum toxicity in terms of tetrodotoxin (TTX) was 25,590 mouse units (MU) per gram for the whole worm throughout the monitoring period. The main toxic component was isolated and recrystallized from an acidified methanolic solution. The crystalline with a specific toxicity of 3520 MU/mg was obtained and identified as TTX by high performance liquid chromatography (HPLC)-fluorescent detection (FLD) (HPLC-FLD), electrospray ionization-mass spectrometry (ESI-MS), infrared (IR), nuclear magnetic resonance (NMR) and gas chromatography-mass spectrometry (GC-MS). The highest toxicity of C. simula exceeded the human lethal dose per a single worm. A toxicological surveillance of C. simula from 1998 to 2005 indicated approximately 80% of the individuals were ranked as "strongly toxic" (≥1000 MU/g). Forty-eight percent of the specimens possessed toxicity scores of more than 2000 MU/g. Seasonal variations were observed in the lethal potency of C. simula. Specimens collected on January 13, 2000 to December 26, 2000 showed mean toxicities of 665-5300 MU/g (n = 10). These data prompted a toxicological surveillance of ribbon worms from other localities with different habitats in Japan, including Akkeshi Bay (Hokkaido) under stones on rocky intertidal beaches, as well as Otsuchi (Iwate) among calcareous tubes of serpulid polychaetes on rocky shores. Within twelve species of ribbon worms examined, only C. simula possessed extremely high toxicity. Therefore, C. simula appears to show generally high toxicity irrespective of their locality and habitat.