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Motivation Compositional heterogeneity—when the proportions of nucleotides and amino acids are not broadly similar across the dataset—is a cause of a great number of phylogenetic artefacts. Whilst a variety of methods can identify it post-hoc, few metrics exist to quantify compositional heterogeneity prior to the computationally intensive task of phylogenetic tree reconstruction. Here we assess the efficacy of one such existing, widely used, metric: Relative Composition Frequency Variability (RCFV), using both real and simulated data. Results Our results show that RCFV can be biased by sequence length, the number of taxa, and the number of possible character states within the dataset. However, we also find that missing data does not appear to have an appreciable effect on RCFV. We discuss the theory behind this, the consequences of this for the future of the usage of the RCFV value and propose a new metric, nRCFV, which accounts for these biases. Alongside this, we present a new software that calculates both RCFV and nRCFV, called nRCFV_Reader. Availability and implementation nRCFV has been implemented in RCFV_Reader, available at: https://github.com/JFFleming/RCFV_Reader. Both our simulation and real data are available at Datadryad: https://doi.org/10.5061/dryad.wpzgmsbpn.

Marenzelleria neglecta Sikorski & Bick, 2004 (Figs 1 & 2) Marenzelleria neglecta Sikorski & Bick, 2004: 264���268, figs 2B, 3C, 5A���I, 6. Syomin et al. 2017: 977���979, figs 2���5. Blank & Bastrop 2009: 316-318, fig. 1 (phylogeny). Marenzelleria viridis: Maciolek 1984 (Part.): 51���55, fig. 2. Bick & Burckhardt 1989: 239���241, fig. 1, pls VII���VIII. Bastrop et al. 1995: Baltic Sea population. Bochert & Bick 1995: 764���772, figs 2���12 (larval morphology). Bochert 1996a: 58���68, figs 1���31 (oogenesis); 1996b: 192���198, figs 1���27 (spermatogenesis). R��hner et al. 1996a: Baltic Sea population. Ysebaert et al. 1996: 178���179. Sikorski & Buzhinskaya 1998: 1118���1119, fig. 4. Fide Sikorski & Bick 2004 (Part.): 264. Not Verrill 1873. ? Marenzelleria viridis: Cohen & Carlton 1995: A4-1. Thompson et al. 2000: 15; 2013: 2290. Cohen et al. 2005: 11. Ranasinghe et al. 2012: 646. Marenzelleria cf. viridis: Bick & Zettler 1997: 141���142, figs 3, 4. Fide Sikorski & Bick 2004: 264. Marenzelleria type II: R��hner et al. 1996b: 281���283. Bastrop et al. 1997: 125���127; 1998: 98���102. Fide Sikorski & Bick 2004: 264. Remarks. Bastrop et al. ���s (1997, 1998) Marenzelleria Type II was found on the both sides of the North Atlantic and not formally named until Sikorski & Bick (2004) described it as a new species, M. neglecta. As noted above, Darss- Zingst-Boddenchain, Baltic Sea, Germany, was designated as the type locality of the species, although M. neglecta was recognized as alien in Europe, being introduced with ballast water from the Atlantic coast of USA (Bastrop et al. 1997, 1998). Based on genetic data (allozyme electrophoresis and/or 16S sequences), Bastrop et al. (1997, 1998) documented the presence of M. neglecta (as M. Type II) in the United States (Durham, New Hampshire; Chesapeake Bay, Maryland; Currituck Sound, North Carolina; Ogeechee River estuary, Georgia) and in Canada (Tuktoyaktuk Harbor, Northwest Territories) (Fig. 2). Notably, specimens of the only sample from New Hampshire (Durham, USNM 80485) were morphologically assigned to M. viridis by Maciolek (1984 *), Sikorski & Bick (2004), as well as one of us (VIR, May 2000). Bastrop et al. (1997: 128) sequenced the 16S mitochondrial fragments of three specimens from this sample and noticed that ���Contradictions between the results of morphological and genetic species determination still exist ��� DNA sequence analysis has shown beyond doubt that these animals [USNM 80485] belong to Marenzelleria Type II [M. neglecta].��� Based on the morphology, Sikorski & Bick (2004) identified M. neglecta from San Francisco Bay (California, USA). After the description of M. neglecta, Leslie H. Harris (in litt. 2 June, 5 July 2021) re-identified as M. neglecta specimens initially reported as M. viridis from California, USA (see below Remarks for M. viridis). Moreover, Leslie H. Harris (in litt. 5 July 2021) identified M. neglecta collected during the 2020 National Coastal Condition Assessment from Ilwaco marina, Columbia River mouth, Washington, USA (see VIR ID 24756 in Table S4). Following these identifications, reports of M. viridis from San Francisco Bay by Thompson et al. (2000, 2013) are also referred herein to M. neglecta. Complete information about records of M. neglecta from North America is given in Table S4. Distribution in North America. Atlantic coast: from New Hampshire south to Georgia, USA. Pacific coast: Washington and Northern California, USA. Arctic coast: Northwest Territories, Canada (Fig. 2). * Maciolek (1984: 52) mistakenly exchanged the catalogue numbers for two specimens collected by Jones, M. L. in Gloucester (Massachusetts) on 16 May 1959 (USNM 80483), and nine specimens collected by Long, C. D. at Fox Point (Durham, New Hampshire) on 24 Jul 1962 (USNM 80485)., Published as part of Radashevsky, Vasily I., Pankova, Victoria V., Malyar, Vasily V., Cerca, Jos�� & Struck, Torsten H., 2021, A review of the worldwide distribution of Marenzelleria viridis, with new records for M. viridis, M. neglecta and Marenzelleria sp. (Annelida: Spionidae), pp. 353-372 in Zootaxa 5081 (3) on pages 360-361, DOI: 10.11646/zootaxa.5081.3.3, http://zenodo.org/record/5775688, {"references":["Sikorski, A. V. & Bick, A. (2004) Revision of Marenzelleria Mesnil, 1896 (Spionidae, Polychaeta). Sarsia, 89 (4), 253 - 275. https: // doi. org / 10.1080 / 00364820410002460","Syomin, V., Sikorski, A., Bastrop, R., Kohler, N., Stradomsky, B., Fomina, E. & Matishov, D. (2017) The invasion of the genus Marenzelleria (Polychaeta: Spionidae) into the Don River mouth and the Taganrog Bay: morphological and genetic study. Journal of the Marine Biological Association of the United Kingdom, 97 (5), 975 - 984. https: // doi. org / 10.1017 / s 0025315417001114","Blank, M. & Bastrop, R. (2009) Phylogeny of the mud worm genus Marenzelleria (Polychaeta, Spionidae) inferred from mitochondrial DNA sequences. Zoologica Scripta, 38 (3), 313 - 321. https: // doi. org / 10.1111 / j. 1463 - 6409.2008.00370. x","Maciolek, N. J. (1984) New records and species of Marenzelleria Mesnil and Scolecolepides Ehlers, (Polychaeta; Spionidae) from Northeastern North America. In: Hutchings, P. A. (Ed.), Proceedings of the First International Polychaete Conference, Sydney. The Linnean Society of New South Wales, Sydney, pp. 48 - 62.","Bick, A. & Burckhardt, R. (1989) Erstnachweis von Marenzelleria viridis (Polychaeta, Spionidae) fur den Ostseeraum, mit einem Bestimmungsschlussel der Spioniden, der Ostee. Mitteilungen aus dem Museum fur Naturkunde in Berlin. Zoologisches Museum und Institut fur Spezielle Zoologie, Berlin, 65 (2), 237 - 247. https: // doi. org / 10.1002 / mmnz. 19890650208","Bastrop, R., Rohner, M. & Jurss, K. (1995) Are there two species of the polychaete genus Marenzellaria in Europe? Marine Biology, Berlin, 121 (3), 509 - 516. https: // doi. org / 10.1007 / BF 00349460","Bochert, R. & Bick, A. (1995) Reproduction and larval development of Marenzelleria viridis (Polychaeta: Spionidae). Marine Biology, Berlin, 123 (4), 763 - 773. https: // doi. org / 10.1007 / BF 00349119","Bochert, R. (1996 a) An electron microscopic study of oogenesis in Marenzelleria viridis (Verrill 1873) (Polychaeta; Spionidae) with special reference to large cortical alveoli. Invertebrate Reproduction and Development, 29 (1), 57 - 69. https: // doi. org / 10.1080 / 07924259.1996.9672495","Rohner, M., Bastrop, R. & Jurss, K. (1996 a) Genetic differences between two allopatric populations (or sibling species) of the polychaete genus Marenzelleria in Europe. Comparative Biochemistry and Physiology, Part B: Biochemistry and Molecular Biology, 114 (2), 185 - 192. https: // doi. org / 10.1016 / 0305 - 0491 (96) 00018 - 1","Ysebaert, T., Meire, P., Block, M. d., Regge, N. d. & Soors, J. (1996) A first record of Marenzelleria viridis (Verrill, 1873) (Polychaeta, Spionidae) in the Schelde estuary (Belgium). Biologisch Jaarboek - Dodonaea, Belgium, 64, 176 - 181.","Verrill, A. E. (1873) Report upon the invertebrate animals of Vineyard Sound and the adjacent waters, with an account of the physical characters of the region. Report of the United States Commission for Fisheries for 1871 - 1872, 1873, 295 - 778.","Cohen, A. N. & Carlton, J. T. (1995) Biological Study. Nonindigenous aquatic species in a United States estuary: a case study of the biological invasions of the San Francisco Bay and Delta. A Report for the United States Fish and Wildlife Service, Washington, D. C., and The National Sea Grant College Program, Connecticut Sea Grant (NOAA Grant Number NA 36 RG 0467). SFEI Contribution No. 185. U. S. Fish and Wildlife Service: Washington, D. C., 246 pp.","Thompson, B., Lowe, S. & Kellogg, M. (2000) Results of the benthic pilot study 1994 - 1997. Part 1, Macrobenthic assemblages of the San Francisco Bay-Delta, and their responses to abiotic factors. Technical Report 39. San Francisco Estuary Institute, Richmond, California, 39 pp.","Thompson, B., Ranasinghe, J. A., Lowe, S., Melwani, A. & Weisberg, S. B. (2013) Benthic macrofaunal assemblages of the San Francisco Estuary and Delta, USA. Environmental Monitoring and Assessment, 185 (3), 2281 - 2295. https: // doi. org / 10.1007 / s 10661 - 012 - 2708 - 8","Cohen, A., Calder, D. R., Carlton, J. T., Chapman, J. W., Harris, L. H., Kitayama, T., Lambert, C. C., Lambert, G., Piotrowski, C., Shouse, M. & Solorzano, L. A. (2005) Rapid Assessment Shore Survey for Exotic Species in San Francisco Bay - May 2004. Final Report for the California State Coastal Conservancy, Association of Bay Area Governments / San Francisco Bay- Delta Science Consortium, National Geographic Society and Rose Foundation. San Francisco Estuary Institute, Oakland, California, 12 pp.","Ranasinghe, J. A., Welch, K. I., Slattery, P. N., Montagne, D. E., Huff, D. D., Lee II, H., Hyland, J. L., Thompson, B., Weisberg, S. B., Oakden, J. M., Cadien, D. B. & Velarde, R. G. (2012) Habitat-related benthic macrofaunal assemblages of bays and estuaries of the western United States. Integrated Environmental Assessment and Management, 8 (4), 638 - 648. https: // doi. org / 10.1002 / ieam. 62","Bick, A. & Zettler, M. L. (1997) On the identity and distribution of two species of Marenzelleria (Polychaeta, Spionidae) in Europe and North America. Aquatic Ecology, 31 (2), 137 - 148. https: // doi. org / 10.1023 / A: 1009995119364","Rohner, M., Bastrop, R. & Jurss, K. (1996 b) Colonization of Europe by two American genetic types or species of the genus Marenzelleria (Polychaeta: Spionidae). An electrophoretic analysis of allozymes. Marine Biology, Berlin, 127 (2), 277 - 287. https: // doi. org / 10.1007 / BF 00942113","Bastrop, R., Rohner, M., Sturmbauer, C. & Jurss, K. (1997) Where did Marenzelleria spp. (Polychaeta: Spionidae) in Europe come from? Aquatic Ecology, 31 (2), 119 - 136. https: // doi. org / 10.1023 / A: 1009994102526","Bastrop, R., Jurss, K. & Sturmbauer, C. (1998) Cryptic species in a marine polychaete and their independent introduction from North America to Europe. Molecular Biology and Evolution, 15 (2), 97 - 103. https: // doi. org / 10.1093 / oxfordjournals. molbev. a 025919"]}

Marenzelleria Mesnil, 1896 Marenzelleria Mesnil, 1896: 120. Augener 1913: 264���267. Fauchald 1977: 24. Maciolek 1984: 48. Sikorski & Buzhinskaya 1998: 1111���1112. Sikorski & Bick 2004: 255. Blank & Bastrop 2009: 311���318. Blake et al. 2020: 50. Type species. Marenzelleria wireni Augener, 1913: 265., Published as part of Radashevsky, Vasily I., Pankova, Victoria V., Malyar, Vasily V., Cerca, Jos�� & Struck, Torsten H., 2021, A review of the worldwide distribution of Marenzelleria viridis, with new records for M. viridis, M. neglecta and Marenzelleria sp. (Annelida: Spionidae), pp. 353-372 in Zootaxa 5081 (3) on page 358, DOI: 10.11646/zootaxa.5081.3.3, http://zenodo.org/record/5775688, {"references":["Mesnil, F. (1896) Etudes de morphologie externe chez les Annelides. I. Les Spionidiens des cotes de la Manche. Bulletin scientifique de la France et de la Belgique, 29 (1), 110 - 287. https: // doi. org / 10.5962 / bhl. part. 19052","Augener, H. (1913) Polychaeten von Franz-Joseph-Land II. Zoologischer Anzeiger, 41, 253 - 273.","Fauchald, K. (1977) The polychaete worms. Definitions and keys to the orders, families and genera. Natural History Museum of Los Angeles County, Science Series, 28, 1 - 188.","Maciolek, N. J. (1984) New records and species of Marenzelleria Mesnil and Scolecolepides Ehlers, (Polychaeta; Spionidae) from Northeastern North America. In: Hutchings, P. A. (Ed.), Proceedings of the First International Polychaete Conference, Sydney. The Linnean Society of New South Wales, Sydney, pp. 48 - 62.","Sikorski, A. V. & Bick, A. (2004) Revision of Marenzelleria Mesnil, 1896 (Spionidae, Polychaeta). Sarsia, 89 (4), 253 - 275. https: // doi. org / 10.1080 / 00364820410002460","Blank, M. & Bastrop, R. (2009) Phylogeny of the mud worm genus Marenzelleria (Polychaeta, Spionidae) inferred from mitochondrial DNA sequences. Zoologica Scripta, 38 (3), 313 - 321. https: // doi. org / 10.1111 / j. 1463 - 6409.2008.00370. x","Blake, J. A., Maciolek, N. J. & Meissner, K. (2020) Spionidae Grube, 1850. In: Purschke, G., Boggemann, M. & Westheide, W. (Eds.), Handbook of Zoology: Annelida. Vol. 2. Pleistoannelida, Sedentaria II. De Gruyter, Berlin, pp. 1 - 103. https: // doi. org / 10.1515 / 9783110291681 - 001"]}

Marenzelleria viridis (Verrill, 1873) (Figs 1���3) Scolecolepis viridis Verrill, 1873: 345, 600���601. Marenzelleria viridis: Maciolek 1984 (Part.): 51���55, fig. 2. Atkins et al. 1987: 311���320, fig. 2. Bastrop et al. 1995: North Sea population. R��hner et al. 1996a: North Sea population. Dauer 1997: 512���515, figs 1, 2 (palp morphology). Sikorski & Bick 2004 (Part.): 261���264, figs 2C, 3B, 4A���F. Bastrop & Blank 2006: 1197���1199. David & Williams 2016: 821���827, figs 1���5 (regeneration). Whitford & Williams 2016: 357���367, figs 1���3 (regeneration). Kauppi et al. 2018: 48���55. Wasmund et al. 2018: 78. O���Reilly & Nowacki 2019: 1���4, fig. 1. Scolecolepides viridis: Hartman 1942: 13. George 1966: 76���92, figs 1���21 (adult, gamete and larval morphology). Foster 1971: 37���40, figs 57���65. Scolelepides viridis: Hartman 1944: 340. Marenzelleria jonesi Maciolek, 1984: 55���58, figs 3, 4. Fide Rodi & Dauer 1996: 72. Marenzelleria type I: R��hner et al. 1996b: 279���281. Bastrop et al. 1997: 125���127; 1998: 98���102. Fide Sikorski & Bick 2004: 264. Marenzelleria cf. wireni: Bick & Zettler 1997: 138���141, figs 1, 2. Fide Sikorski & Bick 2004: 264. Scolecolepis tenuis Verrill, 1873: 345, 601. Fide Foster 1971: 37. Remarks. Verrill (1873) described Scolecolepis viridis based on material from Connecticut, Massachusetts, New Jersey, and Rhode Island, USA. Maciolek (1984) transferred Verrill���s species to Marenzelleria. Sikorski & Bick (2004) established a lectotype and designated the type locality for M. viridis as Naushon Is., off Martha���s Vineyard, Massachusetts (Fig. 2). They also referred to this species Marenzelleria Type I, which was earlier distinguished in genetic studies by R��hner et al. (1996a, b) and Bastrop et al. (1997, 1998). Invasion of North American M. viridis into northern European waters resulted in numerous studies on this species (see brief review in the Introduction). In Europe, M. viridis was collected for the first time in 1979 from the western part of the North Sea: Fourth Estuary (Scotland) (Elliott 1983; Elliott & Kingston 1987; as M. wireni). In 1983, it was recorded from the southern part of the North Sea: Ems Estuary (The Netherlands / Germany) (Essink & Kleef 1988). In the late 1980s���1990s, M. viridis spread over the North Sea and also appeared in the Baltic Sea (see reviews by Essink & Kleef 1993; R��hner et al. 1996b; Bastrop et al. 1997; Zettler 1997; Essink 1999; Olenin & Lepp��koski 1999; Lepp��koski & Olenin 2000; Simm et al. 2003; Bastrop & Blank 2006; Blank & Bastrop 2009; Kauppi et al. 2017, 2018). We collected M. viridis from the Oslofjord in October 2018 and here for the first time report the species for Norwegian waters. Two collected specimens had about 20 narrow yellowish-brown bands on each palp. However, this species was first collected in the region in 2008. A single Marenzelleria specimen was collected from Idefjorden (see VIR ID 24704 in Table S1) and photographed by Fredrick Pleijel in June 2008 (Fig. 3B). Idefjorden is next to the Oslofjord, separating the southern parts of Norway and Sweden (Fig. 3A). The specimen was not preserved, but, according to the features shown on the picture (i.e., about 20 narrow dark bands on each palp, arrangement of branchiae), we identify it as M. viridis. Marenzelleria viridis was reported from San Francisco Bay (California) based upon specimens collected during the Benthic Pilot Study (BPS) in 1994���1997 (Cohen & Carlton 1995; Thompson et al. 2000, 2013; Ranasinghe et al. 2012) and Rapid Assessment Survey (RAS) for Exotic Species in May 2004 (Cohen et al. 2005). No samples were left in public museums from the BPS 1994���1997, but Sikorski & Bick (2004) identified Marenzelleria collected from that same area (Grizzly Bay, a northern embayment of San Francisco Bay; SIO BIC A 660, ZSRO P-869) in 1999 as M. neglecta. Moreover, Leslie H. Harris, who first identified specimens from the RAS-2004 as M. viridis, re-examined the same specimens after the publication of Sikorski & Bick (2004) and referred them to M. neglecta (Harris, L.H., in litt. 2 June 2021). The taxonomists at the San Francisco Public Utilities Commission���s Marine Biology Laboratory, who identified M. viridis specimens cited in Cohen & Carlton (1995), Thompson et al. (2000, 2013) and Ranasinghe et al. (2012), also re-assessed them as M. neglecta following Sikorski & Bick (2004) (Norris, D., pers. comm.). We assume that it might be the only Marenzelleria species widely distributed in San Francisco Bay in areas with low salinity. Carr et al. (2011) reported M. viridis from St. Andrews (New Brunswick, Canada). However, the photos of two specimens (NBPOL181���08, NBPOL262���08) provided by the authors in BOLD (http://boldsystems.org) clearly show features characteristic for Spiophanes Grube, 1860: absence of branchiae, and enlarged neuropodial lamellae of chaetigers 5���13(14) bearing glandular organs. We compared the COI sequences of these specimens (HQ024089, HQ024090) provided by Carr et al. (2011) with those of other spionids and found them nested among Spiophanes, probably representing a new and not yet described species. Chertoprood et al. (2004) reported M. viridis from Kandalaksha Bay of the White Sea (Russia). One of the authors, however, clarified that it was a mistake in the manuscript and that only M. arctia was collected and identified in that study (Udalov, A.A., in litt. 3 Apr 2019). Distribution worldwide. Atlantic coast of North America: from Nova Scotia (Canada) and Maine (USA) south to Delaware (USA). North Europe: Northern Ireland, North Sea, Baltic Sea (Figs 2, 3A)., Published as part of Radashevsky, Vasily I., Pankova, Victoria V., Malyar, Vasily V., Cerca, Jos�� & Struck, Torsten H., 2021, A review of the worldwide distribution of Marenzelleria viridis, with new records for M. viridis, M. neglecta and Marenzelleria sp. (Annelida: Spionidae), pp. 353-372 in Zootaxa 5081 (3) on pages 361-362, DOI: 10.11646/zootaxa.5081.3.3, http://zenodo.org/record/5775688, {"references":["Verrill, A. E. (1873) Report upon the invertebrate animals of Vineyard Sound and the adjacent waters, with an account of the physical characters of the region. Report of the United States Commission for Fisheries for 1871 - 1872, 1873, 295 - 778.","Maciolek, N. J. (1984) New records and species of Marenzelleria Mesnil and Scolecolepides Ehlers, (Polychaeta; Spionidae) from Northeastern North America. In: Hutchings, P. A. (Ed.), Proceedings of the First International Polychaete Conference, Sydney. The Linnean Society of New South Wales, Sydney, pp. 48 - 62.","Atkins, S. M., Jones, A. M. & Garwood, P. R. (1987) The ecology and reproductive cycle of a population of Marenzelleria viridis (Annelida: Polychaeta: Spionidae) in the Tay Estuary. Proceedings of the Royal Society of Edinburgh, Section B: Biological Sciences, 92 (3 - 4), 311 - 322. https: // doi. org / 10.1017 / S 0269727000004735","Bastrop, R., Rohner, M. & Jurss, K. (1995) Are there two species of the polychaete genus Marenzellaria in Europe? Marine Biology, Berlin, 121 (3), 509 - 516. https: // doi. org / 10.1007 / BF 00349460","Rohner, M., Bastrop, R. & Jurss, K. (1996 a) Genetic differences between two allopatric populations (or sibling species) of the polychaete genus Marenzelleria in Europe. Comparative Biochemistry and Physiology, Part B: Biochemistry and Molecular Biology, 114 (2), 185 - 192. https: // doi. org / 10.1016 / 0305 - 0491 (96) 00018 - 1","Dauer, D. M. (1997) Functional morphology and feeding behavior of Marenzelleria viridis (Polychaeta: Spionidae). Bulletin of Marine Science, 60 (2), 512 - 516.","Sikorski, A. V. & Bick, A. (2004) Revision of Marenzelleria Mesnil, 1896 (Spionidae, Polychaeta). Sarsia, 89 (4), 253 - 275. https: // doi. org / 10.1080 / 00364820410002460","Bastrop, R. & Blank, M. (2006) Multiple invasions - a polychaete genus enters the Baltic Sea. Biological Invasions, 8 (5), 1195 - 1200. https: // doi. org / 10.1007 / s 10530 - 005 - 6186 - 6","David, A. A. & Williams, J. D. (2016) The influence of hypo-osmotic stress on the regenerative capacity of the invasive polychaete Marenzelleria viridis from its native range. Marine Ecology, 37 (4), 821 - 830. https: // doi. org / 10.1111 / maec. 12361","Whitford, T. A. & Williams, J. D. (2016) Anterior regeneration in the polychaete Marenzelleria viridis (Annelida: Spionidae). Invertebrate Biology, 135 (4), 357 - 369. https: // doi. org / 10.1111 / ivb. 12148","Kauppi, L., Norkko, A. & Norkko, J. (2018) Seasonal population dynamics of the invasive polychaete genus Marenzelleria spp. in contrasting soft-sediment habitats. Journal of Sea Research, 131, 46 - 60. https: // doi. org / 10.1016 / j. seares. 2017.10.005","Wasmund, N., Dutz, J., Pollehne, F., Siegel, H. & Zettler, M. L. (2018) Biological Assessment of the Baltic Sea 2017. Meereswissenschaftliche Berichte / Marine Science Reports, 108, 1 - 101. https: // doi. org / 10.12754 / msr- 2018 - 0108","O'Reilly, M. & Nowacki, S. (2019) First record of the non-native green palpworm Marenzelleria viridis (Annelida: Spionidae) in the Clyde Estuary. The Glasgow Naturalist, 27 (1), 1 - 4. https: // doi. org / 10.37208 / tgn 27107","Hartman, O. (1942) A review of the types of polychaetous annelids at the Peabody Museum of Natural History, Yale University. Bulletin of the Bingham Oceanographic Collection, 8 (1), 1 - 98.","George, J. D. (1966) Reproduction and early development of the spionid polychaete, Scolecolepides viridis (Verrill). Biological Bulletin, 130 (1), 76 - 93. https: // doi. org / 10.2307 / 1539954","Foster, N. M. (1971) Spionidae (Polychaeta) of the Gulf of Mexico and the Caribbean Sea. Studies on the fauna of Curacao and other Caribbean Islands, 36 (129), 1 - 183.","Hartman, O. (1944) New England Annelida. Part 2. Including the unpublished plates by Verrill with reconstructed captions. Bulletin of the American Museum of Natural History, New York, 82 (7), 331 - 343.","Rodi, A. J. & Dauer, D. M. (1996) Synonymy of Marenzelleria viridis (Verrill) and Marenzelleria jonesi Maciolek (Polychaeta: Spionidae). In: Woodin, S. A., Allen, D. M., Stancyk, S. E., Williams-Howze, J., Feller, R. J., Wethey, D. S., Pentcheff, N. D., Chandler, G. T., Decho, A. W. & Coull, B. C. (Eds.), 24 Annual Benthic Ecology Meeting, Columbia, South Carolina, 1996, pp. 72.","Rohner, M., Bastrop, R. & Jurss, K. (1996 b) Colonization of Europe by two American genetic types or species of the genus Marenzelleria (Polychaeta: Spionidae). An electrophoretic analysis of allozymes. Marine Biology, Berlin, 127 (2), 277 - 287. https: // doi. org / 10.1007 / BF 00942113","Bastrop, R., Rohner, M., Sturmbauer, C. & Jurss, K. (1997) Where did Marenzelleria spp. (Polychaeta: Spionidae) in Europe come from? Aquatic Ecology, 31 (2), 119 - 136. https: // doi. org / 10.1023 / A: 1009994102526","Bastrop, R., Jurss, K. & Sturmbauer, C. (1998) Cryptic species in a marine polychaete and their independent introduction from North America to Europe. Molecular Biology and Evolution, 15 (2), 97 - 103. https: // doi. org / 10.1093 / oxfordjournals. molbev. a 025919","Bick, A. & Zettler, M. L. (1997) On the identity and distribution of two species of Marenzelleria (Polychaeta, Spionidae) in Europe and North America. Aquatic Ecology, 31 (2), 137 - 148. https: // doi. org / 10.1023 / A: 1009995119364","Elliott, M. (1983) The structure and function of the sublittoral benthic populations in the Forth Estuary. Internal report to the Forth River Purification Board, No. ES 4 / 83. Port Edgar Marina, South Queensferry. [unknown pagination]","Elliott, M. & Kingston, P. F. (1987) The sublittoral benthic fauna of the estuary and Firth of Forth, Scotland. Proceedings of the Royal Society of Edinburgh, Section B: Biological Sciences, 93 (3 - 4), 449 - 465. https: // doi. org / 10.1017 / S 0269727000006874","Essink, K. & Kleef, H. L. (1988) Marenzelleria viridis (Verrill, 1873) (Polychaeta: Spionidae): a new record from the Ems Estuary (The Netherlands / Federal Republic of Germany). Zoologische Bijdragen, 38, 3 - 13.","Essink, K. & Kleef, H. L. (1993) Distribution and life cycle of the North American spionid polychaete Marenzelleria viridis (Verrill 1873) in the Ems estuary. Netherlands Journal of Aquatic Ecology, 27 (2 - 4), 237 - 246. https: // doi. org / 10.1007 / BF 02334787","Zettler, M. L. (1997) Bibliography on the genus Marenzelleria and its geographical distribution, principal topics and nomenclature. Aquatic Ecology, 31 (2), 233 - 258.","Essink, K. (1999) Dispersal and development of Marenzelleria spp. (Polychaeta, Spionidae) populations in NW Europe and the Netherlands. Helgolander Meeresuntersuchungen, 52 (3 - 4), 367 - 372. https: // doi. org / 10.1007 / BF 02908910","Olenin, S. & Leppakoski, E. (1999) Non-native animals in the Baltic Sea: alteration of benthic habitats in coastal inlets and lagoons. Hydrobiologia, 393, 233 - 243. https: // doi. org / 10.1023 / A: 1003511003766","Leppakoski, E. & Olenin, S. (2000) Non-native species and rates of spread: lessons from the brackish Baltic Sea. Biological Invasions, 2 (2), 151 - 163. https: // doi. org / 10.1023 / A: 1010052809567","Simm, M., Kukk, H. & Viitasalo, M. (2003) Dynamics of Marenzelleria viridis (Polychaeta: Spionidae) pelagic larvae in Parnu Bay, NE Gulf of Riga, in 1991 - 99. Proceedings of the Estonian Academy of Sciences, Biology and Ecology, 52 (4), 394 - 406. https: // doi. org / 10.3176 / biol. ecol. 2003.4.03","Blank, M. & Bastrop, R. (2009) Phylogeny of the mud worm genus Marenzelleria (Polychaeta, Spionidae) inferred from mitochondrial DNA sequences. Zoologica Scripta, 38 (3), 313 - 321. https: // doi. org / 10.1111 / j. 1463 - 6409.2008.00370. x","Kauppi, L., Norkko, J., Ikonen, J. & Norkko, A. (2017) Seasonal variability in ecosystem functions: quantifying the contribution of invasive species to nutrient cycling in coastal ecosystems. Marine Ecology Progress Series, 572, 193 - 207. https: // doi. org / 10.3354 / meps 12171","Cohen, A. N. & Carlton, J. T. (1995) Biological Study. Nonindigenous aquatic species in a United States estuary: a case study of the biological invasions of the San Francisco Bay and Delta. A Report for the United States Fish and Wildlife Service, Washington, D. C., and The National Sea Grant College Program, Connecticut Sea Grant (NOAA Grant Number NA 36 RG 0467). SFEI Contribution No. 185. U. S. Fish and Wildlife Service: Washington, D. C., 246 pp.","Thompson, B., Lowe, S. & Kellogg, M. (2000) Results of the benthic pilot study 1994 - 1997. Part 1, Macrobenthic assemblages of the San Francisco Bay-Delta, and their responses to abiotic factors. Technical Report 39. San Francisco Estuary Institute, Richmond, California, 39 pp.","Thompson, B., Ranasinghe, J. A., Lowe, S., Melwani, A. & Weisberg, S. B. (2013) Benthic macrofaunal assemblages of the San Francisco Estuary and Delta, USA. Environmental Monitoring and Assessment, 185 (3), 2281 - 2295. https: // doi. org / 10.1007 / s 10661 - 012 - 2708 - 8","Ranasinghe, J. A., Welch, K. I., Slattery, P. N., Montagne, D. E., Huff, D. D., Lee II, H., Hyland, J. L., Thompson, B., Weisberg, S. B., Oakden, J. M., Cadien, D. B. & Velarde, R. G. (2012) Habitat-related benthic macrofaunal assemblages of bays and estuaries of the western United States. Integrated Environmental Assessment and Management, 8 (4), 638 - 648. https: // doi. org / 10.1002 / ieam. 62","Cohen, A., Calder, D. R., Carlton, J. T., Chapman, J. W., Harris, L. H., Kitayama, T., Lambert, C. C., Lambert, G., Piotrowski, C., Shouse, M. & Solorzano, L. A. (2005) Rapid Assessment Shore Survey for Exotic Species in San Francisco Bay - May 2004. Final Report for the California State Coastal Conservancy, Association of Bay Area Governments / San Francisco Bay- Delta Science Consortium, National Geographic Society and Rose Foundation. San Francisco Estuary Institute, Oakland, California, 12 pp.","Carr, C. M., Hardy, S. M., Brown, T. M., Macdonald, T. A. & Hebert, P. D. (2011) A tri-oceanic perspective: DNA barcoding reveals geographic structure and cryptic diversity in Canadian polychaetes. PLoS One, 6 (7), e 22232. https: // doi. org / 10.1371 / journal. pone. 0022232","Grube, A. E. (1860) Beschreibung neuer oder wenig bekannter Anneliden. Archiv fur Naturgeschichte, Berlin, 26 (1), 71 - 118.","Chertoprood, M. V., Udalov, A. A., Stolyarov, A. P. & Borisov, R. R. (2004) Diversity of macrobenthic communities in the White Sea estuaries. Okeanologiya, 44 (6), 901 - 911. [in Russian with English Summary]"]}

Marenzelleria bastropi Bick, 2005 (Figs 1 & 2) Marenzelleria bastropi Bick, 2005: 266���268, figs 1���2. Blank & Bastrop 2009: 314. Marenzelleria sp. A: Bick & Zettler 1997: 143. Sikorski & Bick 2004: 271, fig. 8. Marenzelleria Type III: Bastrop et al. 1997: 126���127; 1998: 99���100. Remarks. By the genetic analyses of Marenzelleria from northern Europe and the US Atlantic coast, R��hner et al. (1996a, b) and Bastrop et al. (1997, 1998) distinguished three lineages of Marenzelleria: Types I, II and III. Marenzelleria Type III was rare and found only in Currituck Sound (North Carolina, USA), co-occurring with Marenzelleria Type II. The worms were not formally named until Bick (2005), based on new material from Currituck Sound, described Marenzelleria Type III as a new species, M. bastropi. It remains known only from its type locality. Complete information about records of M. bastropi is given in Table S3. Distribution. North Carolina, USA (Fig. 2)., Published as part of Radashevsky, Vasily I., Pankova, Victoria V., Malyar, Vasily V., Cerca, Jos�� & Struck, Torsten H., 2021, A review of the worldwide distribution of Marenzelleria viridis, with new records for M. viridis, M. neglecta and Marenzelleria sp. (Annelida: Spionidae), pp. 353-372 in Zootaxa 5081 (3) on page 360, DOI: 10.11646/zootaxa.5081.3.3, http://zenodo.org/record/5775688, {"references":["Bick, A. (2005) A new Spionidae (Polychaeta) from North Carolina, and a redescription of Marenzelleria wireni Augener, 1913, from Spitsbergen, with a key for all species of Marenzelleria. Helgoland Marine Research, 59 (4), 265 - 272. https: // doi. org / 10.1007 / s 10152 - 005 - 0002 - 7","Blank, M. & Bastrop, R. (2009) Phylogeny of the mud worm genus Marenzelleria (Polychaeta, Spionidae) inferred from mitochondrial DNA sequences. Zoologica Scripta, 38 (3), 313 - 321. https: // doi. org / 10.1111 / j. 1463 - 6409.2008.00370. x","Bick, A. & Zettler, M. L. (1997) On the identity and distribution of two species of Marenzelleria (Polychaeta, Spionidae) in Europe and North America. Aquatic Ecology, 31 (2), 137 - 148. https: // doi. org / 10.1023 / A: 1009995119364","Sikorski, A. V. & Bick, A. (2004) Revision of Marenzelleria Mesnil, 1896 (Spionidae, Polychaeta). Sarsia, 89 (4), 253 - 275. https: // doi. org / 10.1080 / 00364820410002460","Bastrop, R., Rohner, M., Sturmbauer, C. & Jurss, K. (1997) Where did Marenzelleria spp. (Polychaeta: Spionidae) in Europe come from? Aquatic Ecology, 31 (2), 119 - 136. https: // doi. org / 10.1023 / A: 1009994102526","Bastrop, R., Jurss, K. & Sturmbauer, C. (1998) Cryptic species in a marine polychaete and their independent introduction from North America to Europe. Molecular Biology and Evolution, 15 (2), 97 - 103. https: // doi. org / 10.1093 / oxfordjournals. molbev. a 025919","Rohner, M., Bastrop, R. & Jurss, K. (1996 a) Genetic differences between two allopatric populations (or sibling species) of the polychaete genus Marenzelleria in Europe. Comparative Biochemistry and Physiology, Part B: Biochemistry and Molecular Biology, 114 (2), 185 - 192. https: // doi. org / 10.1016 / 0305 - 0491 (96) 00018 - 1"]}

Marenzelleria arctia (Chamberlin, 1920) (Figs 1 & 2) Scolecolepides arctius Chamberlin, 1920: 17���18, pl. III, figs 5���7, pl. IV, fig. 1. Marenzelleria arctia: Sikorski & Buzhinskaya 1998: 1115���1118, figs 2, 3. Stolyarov 1994: 67. Burkovsky et al. 1995: 69. Burkovsky & Stolyarov 1995: 36. Sikorski & Buzhinskaya 1998 (Part.): 1115���1118, figs 2, 3. Sikorski 2001: 302���303, textfigs 1���6. Chertoprood et al. 2004: 904���906. Sikorski & Bick 2004: 268���271, figs 2D, F, 3D, 6, 7A���I. Stolyarov & Burkovsky 2004: 422. Bastrop & Blank 2006: 1197���1199. Blank et al. 2008: 129���139. Blank & Bastrop 2009: 313���318. Maximov 2010: 19���31; 2015: 300���310. Kocheshkova & Ezhova 2018: 219���227. Laonice annenkovae Zachs, 1925: 3. Uschakov 1939: 82; 1950: 200; 1955: 265. Fide Sikorski & Buzhinskaya 1998: 1115. Marenzelleria wireni: Annenkova 1932: 176. Vinogradov 1947: 131���132. Sikorski et al. 1988 (Part.): 835���837, fig. 4a���k. Fide Sikorski & Bick 2004: 268. Not Augener 1913. Remarks. Sikorski & Buzhinskaya (1998) transferred Scolecolepides arctius to the genus Marenzelleria and redescribed the species based on the type material (paratypes MCZ ANNb-2194, 2195). They also synonymized Laonice annenkovae Zachs, 1925, from Kola Bay (Barents Sea, Russia) with M. arctia and reported the latter species from the Barents, White, Kara, East Siberian and Bering seas of Russia. Bastrop & Blank (2006) for the first time reported M. arctia from the Baltic Sea based on the results of molecular analysis of specimens collected from the Gulf of Bothnia and around the Isle of Ask�� (Sweden) in 2005. Later, the species was reported from the Gulf of Finland (Finland: Blank et al. 2008; Russia: Maximov 2010, 2015), and south-eastern part of the Baltic Sea (Russia: Kocheshkova & Ezhova 2018). Marenzelleria arctia has not been reported from North America since Chamberlin���s original description. Complete information about type material of M. arctia from the Beaufort Sea, Alaska, is given in Table S2. Distribution in North America. Beaufort Sea, Alaska, USA (Fig. 2)., Published as part of Radashevsky, Vasily I., Pankova, Victoria V., Malyar, Vasily V., Cerca, Jos�� & Struck, Torsten H., 2021, A review of the worldwide distribution of Marenzelleria viridis, with new records for M. viridis, M. neglecta and Marenzelleria sp. (Annelida: Spionidae), pp. 353-372 in Zootaxa 5081 (3) on page 359, DOI: 10.11646/zootaxa.5081.3.3, http://zenodo.org/record/5775688, {"references":["Chamberlin, R. V. (1920) The polychaetes collected by the Canadian Arctic Expedition, 1913 - 18. Report of the Canadian Arctic Expedition 1913 - 18, 9 (B), 1 - 41.","Stolyarov, A. P. (1994) Zonal distribution of macrobenthos in the estuary of Chernaya River (Kandalaksha Bay, White Sea). Zoologicheskii Zhurnal, 73 (4), 65 - 71. [in Russian with English Summary]","Burkovsky, I. V. & Stolyarov, A. P. (1995) Features of macrobenthic structural organisation in conditions with salinity gradient strongly pronounced. Zoologicheskii Zhurnal, 74 (2), 32 - 46. [in Russian with English Summary]","Sikorski, A. V. (2001) Spionidae Grube, 1850. In: Zhirkov, I. A. (Ed.), Polychaeta of the Arctic Ocean. Yanus-K, Moscow, pp. 271 - 332.","Chertoprood, M. V., Udalov, A. A., Stolyarov, A. P. & Borisov, R. R. (2004) Diversity of macrobenthic communities in the White Sea estuaries. Okeanologiya, 44 (6), 901 - 911. [in Russian with English Summary]","Sikorski, A. V. & Bick, A. (2004) Revision of Marenzelleria Mesnil, 1896 (Spionidae, Polychaeta). Sarsia, 89 (4), 253 - 275. https: // doi. org / 10.1080 / 00364820410002460","Stolyarov, A. P. & Burkovsky, I. V. (2004) Structural modification of the estuary macrobenthos during summer period (Kandalaksha Bay, the White Sea). Uspekhi sovremennoj biologii / Advances in current biology, 124 (5), 419 - 428. [in Russian with English Summary]","Bastrop, R. & Blank, M. (2006) Multiple invasions - a polychaete genus enters the Baltic Sea. Biological Invasions, 8 (5), 1195 - 1200. https: // doi. org / 10.1007 / s 10530 - 005 - 6186 - 6","Blank, M., Laine, A. O., Jurss, K. & Bastrop, R. (2008) Molecular identification key based on PCR / RFLP for three polychaete sibling species of the genus Marenzelleria, and the species' current distribution in the Baltic Sea. Helgoland Marine Research, 62 (2), 129 - 141. https: // doi. org / 10.1007 / s 10152 - 007 - 0081 - 8","Blank, M. & Bastrop, R. (2009) Phylogeny of the mud worm genus Marenzelleria (Polychaeta, Spionidae) inferred from mitochondrial DNA sequences. Zoologica Scripta, 38 (3), 313 - 321. https: // doi. org / 10.1111 / j. 1463 - 6409.2008.00370. x","Maximov, A. A. (2010) Changes in bottom communities of the eastern Gulf of Finland after introduction of the polychaete Marenzelleria neglecta. Russian Journal of Biological Invasions, 1 (1), 11 - 16. https: // doi. org / 10.1134 / S 2075111710010030","Kocheshkova, O. V. & Ezhova, E. E. (2018) Polychaetes of Marenzelleria genus (Spionidae) in the Southeastern Baltic Sea (Russian EEZ). Russian Journal of Biological Invasions, 9 (3), 219 - 227. https: // doi. org / 10.1134 / s 2075111718030050","Zachs, I. G. (1925) Nouvelles additions a la faune des Polychaeta du Murman. Comptes Rendus de l'Academie des Sciences de Russie, 1925, 1 - 3.","Uschakov, P. V. (1939) Some new data on polychaetous fauna of the White Sea. Proceedings of the State Geographical Institute, 8, 81 - 84. [in Russian]","Uschakov, P. V. (1950) Polychaetes from the Sea of Okhotsk. Explorations of the Far Eastern Seas of the USSR, 2, 140 - 237. [in Russian]","Uschakov, P. V. (1955) Polychaeta of the Far Eastern Seas of the USSR. Keys to the fauna of the USSR, 56, 1 - 445. [in Russian]","Annenkova, N. (1932) Zur Fauna der \" Polychaeta \" von Franz-Joseph Land. Proceedings of the Institute of Arctic of the Academy of Sciences of the USSR, 2, 153 - 194. [in Russian with German Summary]","Vinogradov, K. A. (1947) Marine fauna of Kamchatka, Pacific Ocean (based on materials collected in Avachinskaya Inlet and Kronotsky Bay in 1932 - 1935). Doctoral Dissertation. Leningrad. [unknown pagination, in Russian]","Sikorski, A. V., Jirkov, I. A. & Tsetlin, A. B. (1988) The genus Laonice (Polychaeta, Spionidae) in the Arctic Ocean: weighting the taxonomic characters and species composition. Zoologicheskii Zhurnal, 67 (6), 826 - 838. [in Russian with English Summary]","Augener, H. (1913) Polychaeten von Franz-Joseph-Land II. Zoologischer Anzeiger, 41, 253 - 273."]}

Marenzelleria sp. (Figs 2, 4���6) Material. Canada, Nunavut, Baffin Is., Koluktoo Bay, 3���21 m, 2018���2020, MIMB 40927, 40928, 42134���42138 (50 spec.). Complete information about this material is given in Table S 5. Description. Anterior fragments and complete juveniles 10���15 mm long, 0.3���0.8 mm wide for 57���88 chaetigers. Fine dark pigment usually scattered on dorsal side of prostomium and 1���2 anterior chaetigers (Fig. 4A���D). Prostomium anteriorly broadly rounded, usually with small incision on frontal margin (Fig. 4A���D), rarely entire. Two pairs of small red eyes arranged trapezoidally; lateral eyes situated anteriorly and set wider apart; occasionally eyes absent. Nuchal organs U-shaped ciliary bands, extending posteriorly to end of chaetiger 2, shorter in small individuals (Figs 4A���D, 5A). Chaetiger 1 well developed, with capillary chaetae and postchaetal lamellae in both rami; notochaetae as long as those on chaetiger 2, arranged in three distinct groups, comprising short anterior-row capillaries with wide limbation, slightly longer posterior-row capillaries with wide limbation, and long thin alimbate superior capillaries. Sabre chaetae in neuropodia from chaetiger 4 onwards in worms of all sizes (Fig. 5E). Hooded hooks in notopodia from chaetigers 24���40, in neuropodia from chaetigers 21���31 onwards (Fig. 5E, F); hooks bidentate with outer hood only and slightly curved shaft (Fig. 4E). Branchiae from chaetiger 1 on anterior half of body (Fig. 5C, D), fused to notopodial postchaetal lamellae at least basally on anterior chaetigers, with surfaces oriented perpendicular to body axis, with ciliation on inner and outer edges (Fig. 4A). Pygidium with up to five pairs of cirri, comprising one pair of short thick ventral cirri, and four pairs of long thin dorsal cirri; dorsal cirri fewer in small individuals (Fig. 5B). Remarks. Marenzelleria species have no unique morphological features and can be distinguished only by the maximum values of morphometric characteristics, such as the length of the nuchal organs, the arrangement of the branchiae and chaetae. Unfortunately, the worms are long and fragile, and mostly anterior fragments are usually available for examination. Sikorski & Bick (2004) and Syomin et al. (2016) provided values of morphometric characteristics for different size classes of M. arctia, M. neglecta, M. viridis, and M. wireni, referring to the worm width at chaetiger 10. However, the values were highly variable and overlapped in individuals of different species less than 1.2 mm wide. Therefore, morphological identification keys have been suggested to be used for large specimens, more than 1.2 mm wide (Sikorski & Bick 2004; Bick 2005). Only these mature individuals have nuchal organs of maximum length, and species-specific arrangement of branchiae and hooded hooks. The Marenzelleria specimens collected in Nunavut (Canada) in August���September 2018 -2020 are up to 0.8 mm wide and have up to 88 chaetigers. They have no gametes and are likely juveniles that cannot be reliably assigned to any particular species. However, the presence of complete specimens in the samples made it possible to describe a series of morphometric relationships between morphological features and the total number of chaetigers, as well as the number of branchiate chaetigers in individuals (Figs 5, 6). Analysis of these relationships shows that new chaetigers in the prepygidial growth zone develop faster than branchiae in individuals up to about 70 chaetigers, while after reaching the stage of about 80 chaetigers, new branchiae develop faster than new chaetigers (Fig. 5C). This means that, in relation to the rate of development of new chaetigers, the development of new branchiae accelerates after about the 80-chaetiger stage. Such acceleration may be expected in order to increase gas exchange in a growing body (body surface is proportional to the square of its linear dimensions, while the volume is proportional to the cube). On the other hand, the rate of loosing of hooded hooks from noto- and neuropodia slows down with age, slightly faster in notopodia than in neuropodia (Fig. 5E). These processes result in an age-related decrease in the number of chaetigers between the starts of hooded hooks in noto- and neuropodia (Fig. 6A), as well as to an agerelated relationship between the arrangement of the branchiae and the hooded hooks (Fig. 6C, D). It is noteworthy that the arithmetic differences between the start of the hooded hooks in noto- and neuropodia (DHH-VHH), as well as between the last branchiate chaetiger and the start of the hooded hooks in noto- (Br-DHH) and neuropodia (Br- VHH), are probably proportionally correlated with the number of the last branchiate chaetiger in individuals (Fig. 6,B, D, F). Although the presented analysis does not include fully developed large individuals, the nuchal organs reaching the end of chaetiger 2 and the high rate of branchial development (Fig. 5C, D) in the examined worms lead us to assume that fully grown adults may have longer nuchal organs and greater number of branchiate chaetigers which are characteristic for M. wireni. This assumption must be confirmed by morphological examination of fully developed large individuals from Nunavut and by analysis of their genetic characteristics. Pending this confirmation, we tentatively refer Canadian specimens to as Marenzelleria sp. Marenzelleria wireni was originally described by Augener (1913) based on specimens from the Barents and Kara Seas. Sikorski & Buzhinskaya (1998) and Sikorski & Bick (2004) re-described the species based on material from all the Eurasian Arctic seas, from the Barents Sea east to the Chukchi Sea. Bick (2005) described worms from Spitsbergen and noted that M. wireni differs from other species by the great number of branchiate chaetigers (branchiae on all chaetigers except the very last) and long nuchal organs (at least up to the end of chaetiger 3/beginning of chaetiger 4). The species has never been reported from North American Arctic region. Distribution in North America. Baffin Is., Nunavut, Canada (Fig. 2)., Published as part of Radashevsky, Vasily I., Pankova, Victoria V., Malyar, Vasily V., Cerca, Jos�� & Struck, Torsten H., 2021, A review of the worldwide distribution of Marenzelleria viridis, with new records for M. viridis, M. neglecta and Marenzelleria sp. (Annelida: Spionidae), pp. 353-372 in Zootaxa 5081 (3) on pages 363-364, DOI: 10.11646/zootaxa.5081.3.3, http://zenodo.org/record/5775688, {"references":["Sikorski, A. V. & Bick, A. (2004) Revision of Marenzelleria Mesnil, 1896 (Spionidae, Polychaeta). Sarsia, 89 (4), 253 - 275. https: // doi. org / 10.1080 / 00364820410002460","Syomin, V. L., Sikorski, A. V., Kovalenko, E. P. & Bulysheva, N. I. (2016) Penetration of genus Marenzelleria (Polychaeta: Spionidae) into the Don River estuary and the Taganrog Bay. Russian Journal of Biological Invasions, 1, 109 - 120. [in Russian with English Summary]","Bick, A. (2005) A new Spionidae (Polychaeta) from North Carolina, and a redescription of Marenzelleria wireni Augener, 1913, from Spitsbergen, with a key for all species of Marenzelleria. Helgoland Marine Research, 59 (4), 265 - 272. https: // doi. org / 10.1007 / s 10152 - 005 - 0002 - 7","Augener, H. (1913) Polychaeten von Franz-Joseph-Land II. Zoologischer Anzeiger, 41, 253 - 273."]}