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.

A new species of heteronemertean with branched proboscis, Gorgonorhynchus albocinctus sp. nov., is described based on the external feature and DNA sequences from a specimen collected subtidally among coral rubbles at a depth of about 6 m in a reef area around Taketomi Island in the Yaeyama Islands, southwestern Japan. It can be classified in the genus because the mode of proboscis branching is dichotomous, rather than alternating laterally. From the two known congeners G. repens Dakin and Fordham, 1931 and G. bermudensis Wheeler, 1940, the new species can be differentiated by having a brown body colour with a white band near the tip of the head. The new species is placed in a molecular phylogenetic context with a maximum-likelihood analysis using the nuclear 18S rRNA and 28S RNA genes, as well as the mitochondrial cytochrome c oxidase subunit I gene, together with 20 species of heteronemerteans, for which those sequences were available in the public databases. The results indicate that G. albocinctus is closely related to Cerebratulus leucopsis (Coe, 1901), a species that is supposed to have a non-branched proboscis.

The morphology of the rhynchocoel blood vessel was studied in 26 specimens representing 14 species of the family Cephalotrichidae. In eight specimens the vascular system could not be traced because of their small size, poor fixation, or contraction during fixation. In the other 18 specimens, a short mid-dorsal rhynchocoel vessel was found. In Cephalothrix adriatica, C. hongkongiensis, C. kefersteini, C. oestrymnica, C. orientalis, C. rufifrons, C. cf. fasciculus and C. cf. simula, the mid-dorsal rhynchocoel vessel penetrates the dorsal side of the proboscis insertion, and extends backward abutting the mid-dorsal rhynchocoel wall (Type A). In C. filiformis sensu Iwata ( 1954 Iwata, F. 1954. The fauna of Akkeshi Bay. XX. Nemertini in Hokkaido. J Fac Sci Hokkaido Univ Ser VI, Zool., 12: 1–39. [Google Scholar] ), the vessel is pendant in the rhynchocoel above the proboscis (Type B). In C. filiformis s.str., the vessel runs in the proboscis wall, after passing through the proboscis insertion (Type C). Morphology of the rhynchocoelic vessel might have taxonomic significance in cephalothrichids.