Cephalothrix simula -

Cephalothrix simula naturally occurs in the northwestern Pacific Ocean ^[2].

First observation in Belgium

In 2015, Cephalothrix cf. simula was first collected on the eastern side of the Verbindingsdok and on the left bank of the Boudewijn Canal near Zwankendamme, in the inner port of Zeebrugge ^[3].
 

Distribution in Belgium

In 2016, similar findings were again made in Zeebrugge, in the Verbindingsdok and the Boudewijn Canal, and in 2017, the species was once more recorded at the latter location ^[3]. In 2020, Cephalothrix simula was also collected in the Oud Ferrydok in the inner port of Zeebrugge ^[4] and in 2024, several specimens, presumably Cephalothrix simula, were found in mussel clumps from the Boudewijn Canal ^[5].
 

Distribution in neighbouring countries

In 2012/2013, four specimens of Cephalothrix simula were discovered in the Eastern Scheldt in the Netherlands, one near Zierikzee and three specimens near Sint-Annaland ^[6].

Based on DNA research from 2010 and 2013, Cephalothrix simula had already been detected in several locations across Europe, such as along the Atlantic (Galicia, Asturias, and Cantabria) and Mediterranean (Catalonia) coasts of Spain, as well as the Italian Adriatic coast (Trieste) ^[7,8]. In 2015, additional Mediterranean findings were recorded along the Spanish coast (Valencia, Murcia, and Andalusia) ^[9,10]. Further genetic research on Cephalothrix species collected in Europe during the period 2011-2017 provided both new and confirming location data for Cephalothrix simula in France (Roscoff, Concarneau), Spain (Blanes), and Italy (Giglio) ^[11]. In 2018, the species was also observed in the southwest of Cornwall (United Kingdom) ^[12]. Through the 2010 DNA research, the species was also identified on the west coast of North America in San Diego Bay (California) ^[7] and in 2019-2020 in Bodega Harbor, north of San Francisco ^[13].

The exact method of introduction has not yet been determined, but it is likely that this worm entered European waters via ballast water of ships, through fouling on ship hulls, or via international transport of shellfish for aquaculture purposes ^[12,14,15]. The ballast water hypothesis is supported by the fact that Cephalothrix larvae were found in ballast water in the port of Vladivostok ^[16]. Some authors suggest multiple and independent introductions in southern and western Europe ^[8], a plausible hypothesis that, based on current data, has not yet been confirmed ^[6].

In Zierikzee, Cephalothrix simula was found among fouling bryozoans/hydrozoans and other invertebrates on shallow stones of the dike slope along the shore of the Eastern Scheldt. In Sint-Annaland, they were discovered at a depth of 14 meters, just below the dike slope on a sandy substrate between Sand mason worms (Lanice conchilega), which may serve as food for the ribbon worm [6,14]. Little to no information is available regarding the species' tolerance to physicochemical parameters such as temperature and salinity.

Environmental changes due to climate change may further facilitate the establishment of this species in the Mediterranean region and the Atlantic Ocean. The presence of developed gonads in a specimen, as well as the detection of juvenile individuals, indicates that reproduction is occurring in the colonised areas ^[8]. Rapid natural spread is considered unlikely, suggesting that human activities are likely responsible for the colonisation of new areas ^[8]. However, further dispersal of this species from already established populations via ocean currents cannot be ruled out ^[12,17].

No studies have been conducted on the potential impact of Cephalothrix simula in newly colonised areas ^[12]. As with all introductions, this species, as a predator, will likely affect the local food chain to some extent ^[6]. In some Mediterranean samples, Cephalothrix simula accounted for 28% of all ribbon worms, with the native Cephalothrix species absent, possibly indicating competitive exclusion. However, there is insufficient data to support this hypothesis ^[8]. Additionally, the high toxicity of this species (discussed later) could limit predation by native species, potentially promoting further establishment or spread. More research on its distribution (including molecular tools due to the complex identification), impact, and the (health) risks associated with its presence is necessary to inform policy ^[12].

Cephalothrix simula contains the neurotoxin tetrodotoxin (TTX), which is also found in highly poisonous pufferfish, blue-ringed octopuses, and some species of shellfish, crustaceans, echinoderms, and various marine worms ^[18]. Tetrodotoxin is produced by the bacterium Cytobacillus gottheilii, which resides in the host's body ^[19]. Cephalothrix cf. simula is capable of storing extremely high concentrations of the toxin in its tissues ^[20], although the amount of toxin varies between individuals [14]. In one case, a single worm was found to contain the minimum lethal dose of TTX for humans (24 mg) ^[21]. Nearly half of the examined worms contained approximately 20% of this dose ^[6]. Therefore, the risk that TTX-positive ribbon worms could enter the food chain through predation must be carefully analysed ^[12]. In Japan, toxic ribbon worms were found on the shells of oysters in commercial aquaculture, but it was concluded that the oysters were safe to eat as the worms were removed during the cleaning process ^[21,22]. In 2024, several specimens of a ribbon worm (most likely Cephalothrix simula) were also found among the byssus threads of mussel clumps in the Boudewijn Canal ^[5]. On the other hand, the ribbon worm itself benefits from a symbiotic advantage, using the toxin as a defense mechanism against predation and/or as a means of subduing prey during foraging ^[20,23].

Cephalothrix simula has a cylindrical body, lacking eyes, with a mouth that has evolved into a large lip forming a suction cup. Its color ranges from dark yellow, light orange to reddish-yellow. These worms can grow up to 20 cm in length (when stretched) and 2 mm in thickness, though they can also be much smaller and thinner ^[8,14]. Their appearance resembles the native species Cephalotrix rufifrons, but the latter only reaches a maximum thickness of 1 mm ^[14,24]. Often, DNA analysis is required to distinguish between different ribbon worms ^{[6-8,11,12,15,25]}. For a more detailed and often complex technical species description, reference is made to the relevant literature ^[8,13,25-27]. The complete genome sequence of Cephalothrix simula was already published in 2009 ^[28].

Most nemerteans are carnivorous predators and/or scavengers, while some groups have adopted a different lifestyle (e.g., symbiotic or purely pelagic) ^[29]. In addition to specific characteristics of the mouth and digestive tract, the nature of and the way ribbon worms use their extendable proboscis largely determines their feeding behavior ^[30]. In laboratory conditions, it has been shown that Cephalothrix simula feeds on annelids (polychaetes and oligochaetes) ^[31], while stomach content analyses also indicate predation on amphipods, isopods, and even other ribbon worms ^[16]. Nematodes are also on the menu of Cephalothrix species, and cannibalism has also been observed ^[30]. Species from this genus appear to be able to detect prey from a distance, possibly through a chemotactic mechanism ^[32]. In the Eastern Scheldt, Cephalothrix simula was found in dense populations of Sand mason worms (Lanice conchilega) and Nicolea zostericola, which may serve as its food ^[6,14].

Little is known about the reproductive behavior of ribbon worms. In species of the class Palaeonemertea, to which the genus Cephalothrix belongs, fertilisation occurs externally and sexually. Male and female reproductive cells are released by one or more individuals of both sexes into a gelatinous sheath. After fertilisation, the worms leave the sheath, and a gelatinous egg string is formed. Inside, the embryos develop into larvae, which then hatch and, without further larval metamorphosis, grow directly into miniature ribbon worms ^{[24,29,33,34]}. Reproduction mainly takes place during the summer months.

[1]          World Register of Marine Species (WoRMS) (2024). Cephalothrix simula (Iwata, 1952). https://www.marinespecies.org/aphia.php?p=taxdetails&id=573293 (2024-10-18).

[2]          Kajihara, H. (2007). A taxonomic catalogue of Japanese nemerteans (Phylum Nemertea). Zool. Sci. 24(4): 287-326. [https://www.vliz.be/en/imis?module=ref&refid=394233] 

[3]          Data monitoring eCOAST. Faasse, M. Persoonlijke mededeling.

[4]          Faase, M., Dumoulin, E. (2024). Persoonlijke mededeling.

[5]          Dumoulin, M. (2024). Persoonlijke mededeling.

[6]          Faasse, M.A.; Turbeville, J.M. (2015). The first record of the north-west Pacific nemertean Cephalothrix simula in northern Europe. Marine Biodiversity Records 8(e17). [https://www.vliz.be/nl/imis?module=ref&refid=282170] 

[7]          Chen, H.; Strand, M.; Norenburg, J.L.; Sun, S.; Kajihara, H.; Chernyshev, A.V.; Maslakova, S.A.; Sundberg, P. (2010). Statistical parsimony networks and species assemblages in cephalotrichid nemerteans (Nemertea). PLoS One 5(9): e12885. [https://www.vliz.be/en/imis?module=ref&refid=394232] 

[8]          Fernandez-Alvarez, F.A.; Machordom, A. (2013). DNA barcoding reveals a cryptic nemertean invasion in Atlantic and Mediterranean waters. Helgol. Mar. Res. 67(3): 599-605. [https://www.vliz.be/en/imis?module=ref&refid=394230] 

[9]          Herrera-Bachiller, A.; Fernandez-Alvarez, F.A.; Junoy, J. (2015). A taxonomic catalogue of the nemerteans (Phylum Nemertea) of Spain and Portugal. Zool. Sci. 32(6): 507-522. [https://www.vliz.be/nl/imis?module=ref&refid=395807]

[10]        Herrera-Bachiller, A. (2016). Los nemertinos de España y Portugal. PhD Thesis. Universidad de Alcalá. Departamento de Ciencias de la Vida: Alcalá de Henares. 441 pp. [https://www.vliz.be/nl/imis?module=ref&refid=395808] 

[11]        Sagorny, C.; Wesseler, C.; Krämer, D.; von Döhren, J. (2019). Assessing the diversity and distribution of Cephalothrix species (Nemertea: Palaeonemertea) in European waters by comparing different species delimitation methods. J. Zoo. Syst. Evol. Research 57(3): 497-519. [https://www.vliz.be/nl/imis?module=ref&refid=395809] 

[12]        Turner, A.D.; Fenwick, D.; Powell, A.; Dhanji-Rapkova, M.; Ford, C.; Hatfield, R.G.; Santos, A.; Martinez-Urtaza, J.; Bean, T.P.; Baker-Austin, C.; Stebbing, P. (2018). New invasive nemertean species (Cephalothrix simula) in England with high levels of tetrodotoxin and a microbiome linked to toxin metabolism. Mar. Drugs 16(11): 452. [https://www.vliz.be/nl/imis?module=ref&refid=303850] 

[13]        Ellison, C.I.; Frey, M.R.; Sanford, E.; Maslakova, S. (2024). Ribbon worms (phylum Nemertea) from Bodega Bay, California: A largely undescribed diversity. ZooKeys 1204: 15-64. [https://www.vliz.be/en/imis?module=ref&refid=393402] 

[14]        van Bragt, P.H. (2015). Giftige nieuwe soort snoerworm in onze kustwateren aangetroffen. Nature Today 19 juli: online. https://www.naturetoday.com/intl/nl/nature-reports/message/?msg=21677 [https://www.vliz.be/en/imis?module=ref&refid=394229] 

[15]        Kajihara, H.; Sun, S.-C.; Chernyshev, A.V.; Chen, H.-X.; Ito, K.; Asakawa, M.; Maslakova, S.A.; Norenburg, J.L.; Strand, M.; Sundberg, P.; Iwata, F. (2013). Taxonomic identity of a tetrodotoxin-accumulating ribbon-worm Cephalothrix simula (Nemertea: Palaeonemertea): A species artificially introduced from the Pacific to Europe. Zool. Sci. 30(11): 985-997. [https://www.vliz.be/en/imis?module=ref&refid=394228] 

[16]        Chernyshev, A.V. (2014). Nemertean biodiversity in the Sea of Japan and adjacent areas, in: Song, S. et al. Marine biodiversity and ecosystem dynamics of the Northwest Pacific Ocean. pp. 119-135. [https://www.vliz.be/en/imis?module=ref&refid=394226]  

[17]        Pingree, R.D.; Le Cann, B. (1990). Structure, strength and seasonality of the slope currents in the Bay of Biscay region. J. Mar. Biol. Ass. U.K. 70(4): 857-885. [https://www.vliz.be/en/imis?module=ref&refid=394224] 

[18]        Magarlamov, T.Y.; Beleneva, I.A.; Chernyshev, A.V.; Kuhlevsky, A.D. (2014). Tetrodotoxin-producing Bacillus sp. from the ribbon worm (Nemertea) Cephalothrix simula (Iwata, 1952). Toxicon 85: 46-51. [https://www.vliz.be/nl/imis?module=ref&refid=395810] 

[19]        Melnikova, D.I.; Nijland, R.; Magarlamov, T.Y. (2021). The first data on the complete genome of a tetrodotoxin-producing bacterium. Toxins 13(6): 410. [https://www.vliz.be/nl/imis?module=ref&refid=395811] 

[20]        Malykin, G.V.; Chernyshev, A.V.; Magarlamov, T.Y. (2021). Intrabody tetrodotoxin distribution and possible hypothesis for its migration in ribbon worms Cephalothrix cf. simula (Palaeonemertea, Nemertea). Mar. Drugs 19(9): 494. [https://www.vliz.be/nl/imis?module=ref&refid=395812] 

[21]        Asakawa, M.; Ito, K.; Kajihara, H. (2013). Highly toxic ribbon worm Cephalothrix simula containing tetrodotoxin in Hiroshima Bay, Hiroshima Prefecture, Japan. Toxins 5(2): 376-395. [https://www.vliz.be/en/imis?module=ref&refid=394223]

[22]        Asakawa, M.; Toyoshima, T.; Shida, Y.; Noguchi, T.; Miyazawa, K. (2000). Paralytic toxins in a ribbon worm Cephalothrix species (Nemertean) adherent to cultured oysters in Hiroshima Bay, Hiroshima Prefecture, Japan. Toxicon 38(6): 763-773. [https://www.vliz.be/en/imis?module=ref&refid=394222] 

[23]        Goransson, U.; Jacobsson, E.; Strand, M.; Andersson, H.S. (2019). The toxins of nemertean worms. Toxins 11(2): 120. [https://www.vliz.be/en/imis?module=ref&refid=310869] 

[24]        Gibson, R. (1994). Nemerteans: keys and notes for identification of the species. Revised edition. Synopses of the British Fauna, N.S. 24. Field Studies Council: Shrewsbury. ISBN 1-85153-253-6. VII, 224 pp. [https://www.vliz.be/en/imis?module=ref&refid=19687]

[25]        Kajihara, H. (2017). Species diversity of Japanese ribbon worms (Nemertea), in: Motokawa, M. et al. Species diversity of animals in Japan. pp. 419-444. [https://www.vliz.be/en/imis?module=ref&refid=366852] 

[26]        Iwata, F. (1952). Nemertini from the coasts of Kyusyu. Jour. Fac. Sci. Hokkaido Univ., Ser. VI, Zool. 11(1): 126-148. [https://www.vliz.be/nl/imis?module=ref&refid=395813] 

[27]        Iwata, F. (1954). The fauna of Akkeshi Bay: XX. Nemertini in Hokkaido (revised report) . Jour. Fac. Sci. Hokkaido Univ., Ser. VI, Zool. 12(1-2): 1-39. [https://www.vliz.be/nl/imis?module=ref&refid=395814] 

[28]        Chen, H.-X.; Sundberg, P.; Norenburg, J.L.; Sun, S.-C. (2009). The complete mitochondrial genome of Cephalothrix simula (Iwata) (Nemertea: Palaeonemertea). Gene 442(1-2): 8-17. [https://www.vliz.be/nl/imis?module=ref&refid=395815] 

[29]        Gibson, R. (1972). Nemerteans. Hutchinson University Library: London. 224 pp. [https://www.vliz.be/nl/imis?module=ref&refid=395817] 

[30]        McDermott, J.J.; Roe, P. (1985). Food, feeding behavior and feeding ecology of nemerteans. Am. Zool. 25(1): 113-125. [https://www.vliz.be/nl/imis?module=ref&refid=395818] 

[31]        Wang, H.; Sun, S.; Li, Q. (2008). Laboratory observations on the feeding behavior and feeding rate of the nemertean Procephalothrix simulus. Biol. Bull. 214(2): 166-175. [https://www.vliz.be/en/imis?module=ref&refid=394221] 

[32]        Jennings, J.B.; Gibson, R. (1969). Observations on the nutrition of seven species of rhynchocoelan worms. Biol. Bull. 136(3): 405-433. [https://www.vliz.be/nl/imis?module=ref&refid=395819] 

[33]        Iwata, F. (1960). Studies on the comparative embryology of nemerteans with special reference to their interrelationship. Publ. Akkeshi Mar. Biol. Stat. 10: 1-51. [https://www.vliz.be/nl/imis?module=ref&refid=395820] 

[34]        Smith, J.E. (1935). The early development of the nemertean Cephalothrix rufifrons. J. Cell Sci. Ser.2, 77(307): 335-381. [https://www.vliz.be/nl/imis?module=ref&refid=395821]

VLIZ Alien Species Consortium (2024). Cephalothrix simula. Introduced alien species of the Belgian part of the North Sea and adjacent estuaries anno 2024. Flanders Marine Institute (VLIZ). 7 pp.