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We present the first DNA taxonomy publication on abyssal Mollusca from the Clarion-Clipperton Zone (CCZ), central Pacific ocean, using material collected as part of the Abyssal Baseline (ABYSSLINE) environmental survey cruise 'AB01' to the UK Seabed Resources Ltd (UKSRL) polymetallic-nodule exploration area 'UK-1' in the eastern CCZ. This is the third paper in a series to provide regional taxonomic data for a region that is undergoing intense deep-sea mineral exploration for high-grade polymetallic nodules. Taxonomic data are presented for 21 species from 42 records identified by a combination of morphological and genetic data, including molecular phylogenetic analyses. These included 3 heterodont bivalves, 5 protobranch bivalves, 4 pteriomorph bivalves, 1 caudofoveate, 1 monoplacophoran, 1 polyplacophoran, 4 scaphopods and 2 solenogastres. Gastropoda were recovered but will be the subject of a future study. Seven taxa matched published morphological descriptions for species with deep Pacific type localities, and our sequences provide the first genetic data for these taxa. One taxon morphologically matched a known cosmopolitan species but with a type locality in a different ocean basin and was assigned the open nomenclature 'cf' as a precautionary approach in taxon assignments to avoid over-estimating species ranges. One taxon is here described as a new species, Ledella knudseni sp. n. For the remaining 12 taxa, we have determined them to be potentially new species, for which we make the raw data, imagery and vouchers available for future taxonomic study. The Clarion-Clipperton Zone is a region undergoing intense exploration for potential deep-sea mineral extraction. We present these data to facilitate future taxonomic and environmental impact study by making both data and voucher materials available through curated and accessible biological collections.

Adenopilina adenensis (Tebble, 1967) Neopilina adenensis Tebble 1967: 663, figs 1���3. This species represents the sole record of a monoplacophoran from the Indian Ocean, it was described from the Alula��Fartak trench in the Gulf of Aden (13 �� 50 'N, 51 �� 47 'E), where it was collected between depths of 3000���3950 m. Genus Laevipilina McLean, 1979 Type species: Vema (Laevipilina) hyalina McLean, 1979, by original designation., Published as part of Schwabe, Enrico, 2008, A summary of reports of abyssal and hadal Monoplacophora and Polyplacophora (Mollusca) *, pp. 205-222 in Zootaxa 1866 on pages 206-207, DOI: 10.5281/zenodo.183815, {"references":["Tebble, N. (1967) A Neopilina from the Gulf of Aden. Nature, 215, 663 - 664.","McLean, J. H. (1979) A new monoplacophoran limpet from the continental shelf of southern California. Contributions in Science of the Natural History Museum of Los Angeles County, 307, 1 - 19."]}

Veleropilina veleronis (Menzies & Layton, 1962) Neopilina (Vema) sp. Menzies & Robinson 1961: 338, fig. 1. Neopilina (Neopilina) veleronis Menzies & Layton 1962: 402, pl. 7, figs A–F, pl. 8, fig. G, pls 9, 10. The 14 specimens known from the original description are all from the type locality: Mexico, Baja California, off Cedros Island, slope of the Cedros Trench, 30 miles off Natividad Island light (27 ° 52 ' 25 ''­ 27 ° 51 ' 30 ''N, 115 ° 44 ' 30 ''­ 115 ° 45 ' 15 ''W) and were collected at a depth between 2730–2769 m. Apart from the shallow water species Micropilina arntzi Warén & Hain, 1992 (17), and the abyssal species Ve ma e wi ng i (Clarke & Menzies, 1959) (11) and Neopilina galatheae Lemche, 1957 (10), this species was most numerous at a single station (14). Genus Ve ma Clarke & Menzies, 1959 Type species: Neopilina (Vema) ewingi Clarke & Menzies, 1959, by original designation.

Laevipilina antarctica War��n & Hain, 1992 Laevipilina antarctica War��n & Hain 1992: 167, figs 2 ���5, 6���8, 10���16, 19, 27. This species, originally described from the Weddell and Lazarev seas, Antarctica, had a bathymetric range from 210���644 m (War��n & Hain 1992). Recent additional reports by Schr��dl et al. (2006) include a first abyssal record for this species. The abyssal specimen comes from soft bottom terraces 3 km to the SW edge of the Wegener Canyon (70 �� 38.46 ���S, 14 �� 42.87 ���W ��� 70 �� 39.19 ���S, 14 �� 43.44 ���W), Weddell Sea, where it was collected at 3102���3136 m depth. This was not only a considerably range extension but also the first indication that this genus is found at abyssal depths. Genus Monoplacophorus Moskalev, Starobogatov & Filatova, 1983 Type species: Monoplacophorus zenkevitchi Moskalev, Starobogatov & Filatova, 1983, by original designation., Published as part of Schwabe, Enrico, 2008, A summary of reports of abyssal and hadal Monoplacophora and Polyplacophora (Mollusca) *, pp. 205-222 in Zootaxa 1866 on page 207, DOI: 10.5281/zenodo.183815, {"references":["Waren, A. & Hain, S. (1992) Laevipilina antarctica and Micropilina arntzi, two new monoplacophorans from the Antarctic. The Veliger, 35 (3), 165 - 176.","Moskalev, L. I., Starobogatov, Y. I. & Filatova, Z. A. (1983) New data on the abyssal Monoplacophora from the Pacific and South Atlantic Oceans. Zoologiceskij Zurnal, 62 (7), 981 - 996."]}

Rokopella brummeri Goud & Gittenberger, 1993 Rokopella brummeri Goud & Gittenberger 1993: 74, figs 1–10. This is so far the single record of an abyssal monoplacophoran from the northern Atlantic Ocean. The species was described from east of the Mid­Atlantic Ridge (45 ° 21.3 'N, 27 °09.1'W) from a depth of 2162 m.

Rokopella oligotropha (Rokop, 1972) Neopilina (Neopilina) oligotropha Rokop 1972: 91, figs 1���9. Only one specimen and a shell fragment of this species have so far been collected at abyssal depths. The species was described from the central North Pacific, approximately 680 miles north of Hawaii (30 ��05'N, 156 �� 11 ' 48 ''W), 6065���6079 m. Genus Veleropilina Starobogatov & Moskalev, 1987 Type species: Neopilina veleronis Menzies & Layton, 1963, by original designation., Published as part of Schwabe, Enrico, 2008, A summary of reports of abyssal and hadal Monoplacophora and Polyplacophora (Mollusca) *, pp. 205-222 in Zootaxa 1866 on page 209, DOI: 10.5281/zenodo.183815, {"references":["Rokop, F. J. (1972) A new species of Monoplacophoran from the Abyssal North Pacific. The Veliger, 15 (2), 91 - 95.","Menzies, R. J. (1963) General results of Biological Investigations on the deep-sea fauna made on the U. S. N. S. Elatnin (U. S. A. R. P.) during cruise 3 between Panama and Valparaiso, Chile in 1962. Internationale Revue der gesamten Hydrobiologie, 48 (2), 185 - 200."]}

A summary of literature records of Polyplacophora and Monoplacophora from below 2000 m is presented. Reports have been published of 11 described species of monoplacophorans and twice as many polyplacophorans from abyssal and hadal depths. Additionally taken into account are several records of deep water species of uncertain taxonomic position in both classes. Occurrence and geographic distribution are briefly discussed.

Veleropilina sp. unidentified Monoplacophora Levin & Lonsdale 1983: 1017. Veleropilina sp. Warén & Gofas 1996: 222, figs 1 D, 8 A, B, 9 E, F, 10 A–C, 15 A. The species is here included in the list of species from below 2000 m, because the record of the single specimen: off the southern point of Baja California (20 ° 48.5 'N, 109 ° 17.4 'W), 1950 m depth at a submarine volcano, was close enough to 2000 m that it is likely that it also occurs somewhat deeper.

Neopilina rebainsi Moskalev, Starobogatov & Filatova, 1983 Neopilina (Neopilina) sp. Filatova et al. 1974: 675. Neopilina (Lemchephyala) rebainsi Moskalev, Starobogatov & Filatova 1983: 988, figs 5, 7��� 9. The holotype is known from the following locality: Southeast of the Falkland Islands (56 ��29.0'S, 50 �� 51.1 'W), 4660���5630 m. Neopilina of uncertain taxonomic position �� 18 specimens of Neopilina sp. from the southeastern Pacific, Peru��Chile Trench, 2000���6000 m (Menzies 1963) �� number of specimens unknown; as Neopilina sp. from the southeastern Pacific, Milne Edwards Deep of the Peru��Chile Trench, southeastern Pacific (08�� 52 'S, 80 �� 47 'W), 6146���6313 m (Menzies 1968) �� number of specimens unknown; as Neopilina sp. from the southeastern Pacific, Milne Edwards Deep of the Peru��Chile Trench, southeastern Pacific (08�� 46 'S, 80 �� 44 'W), 3909���3970 m (Menzies 1968) �� number of specimens unknown; as Neopilina sp. from the southeastern Pacific, Milne Edwards Deep of the Peru��Chile Trench, southeastern Pacific (11 �� 30 'S, 79 �� 25 'W), 6146���6354 m (Menzies 1968) �� 1 specimen mentioned as Neopilina (Neopilina) sp. from the northwestern Scotia Ridge, southeast of the Falkland Islands (54 �� 43 '�� 54 �� 45 'S, 55 �� 3 '�� 55 �� 37 'W), 1647���2044 m (Rosewater 1970) �� 1 specimen mentioned as Neopilina sp. from the southeastern Pacific off Chile (23 �� 50 'S, 71 ��06'W), 4600 m (Moskalev et al. 1983) Genus Rokopella Starobogatov & Moskalev, 1987 Type species: Neopilina oligotropha Rokop, 1972, by original designation., Published as part of Schwabe, Enrico, 2008, A summary of reports of abyssal and hadal Monoplacophora and Polyplacophora (Mollusca) *, pp. 205-222 in Zootaxa 1866 on page 208, DOI: 10.5281/zenodo.183815, {"references":["Moskalev, L. I., Starobogatov, Y. I. & Filatova, Z. A. (1983) New data on the abyssal Monoplacophora from the Pacific and South Atlantic Oceans. Zoologiceskij Zurnal, 62 (7), 981 - 996.","Filatova, Z. A., Vinogradova, N. G. & Moskalev, L. I. (1974) New finding of the ancient primitive mollusc Neopilina in the Atlantic part of the Antarctica. Nature, 249, 675.","Menzies, R. J. (1963) General results of Biological Investigations on the deep-sea fauna made on the U. S. N. S. Elatnin (U. S. A. R. P.) during cruise 3 between Panama and Valparaiso, Chile in 1962. Internationale Revue der gesamten Hydrobiologie, 48 (2), 185 - 200.","Menzies, R. J. (1968) New species of Neopilina of the Cambro-Devonian class Monoplacophora from the Milne- Edwards deep of the Peru-Chile Trench, R / V Anton Bruun. Marine Biological Association of India, Proceedings of the Symposium on Mollusca, 1, 1 - 9.","Rosewater, J. (1970) Monoplacophora in the South Atlantic Ocean. Science, 167, 1485 - 1486.","Rokop, F. J. (1972) A new species of Monoplacophoran from the Abyssal North Pacific. The Veliger, 15 (2), 91 - 95."]}

Neopilina bruuni Menzies, 1968 Neopilina (Neopilina) bruuni Menzies 1968: 2, figs 1 c, 4 A���E, 5. Although the holotype was originally described from the Anton Bruun Cruise 11, Station 197 (from the southeastern Pacific, Milne Edwards Deep of the Peru��Chile Trench: 11 �� 30 'S, 79 �� 25 'W, 6146���6354 m), a few pages later (p. 8) the author listed the species being from Station 179: Milne Edwards Deep of the Peru��Chile Trench, Southeast Pacific (08�� 54 'S, 80 �� 41 'W). It is most likely that this latter station is correct and the original ��� 197 ��� numbers were mixed up, as other monoplacophorans were reported from Station 197 (Vema ewingi (Clarke & Menzies, 1959; Neopilina sp.), and no other monoplacophoran was listed under this station (which indicates that the species was not mixed). It seems necessary to restrict the type locality to Station 179. The holotype was thus found at a depth of 4823���4925 m as cited without comments in recent works (e.g., War��n & Hain 1992, Counts 2006, Haszprunar 2008)., Published as part of Schwabe, Enrico, 2008, A summary of reports of abyssal and hadal Monoplacophora and Polyplacophora (Mollusca) *, pp. 205-222 in Zootaxa 1866 on page 207, DOI: 10.5281/zenodo.183815, {"references":["Menzies, R. J. (1968) New species of Neopilina of the Cambro-Devonian class Monoplacophora from the Milne- Edwards deep of the Peru-Chile Trench, R / V Anton Bruun. Marine Biological Association of India, Proceedings of the Symposium on Mollusca, 1, 1 - 9.","Clarke, A. H. & Menzies, R. J. (1959) Neopilina (Vema) ewingi, a second living species of the Paleozoic class Monoplacophora. Science, 129, 1026 - 1027.","Waren, A. & Hain, S. (1992) Laevipilina antarctica and Micropilina arntzi, two new monoplacophorans from the Antarctic. The Veliger, 35 (3), 165 - 176.","Counts (III.), C. L. (2006) Chapter 17: Monoplacophora. pp. 211 - 216. In: Sturm, C. F., Pearce, T. A. & Valdes, A. (eds) The Mollusks: A Guide to Their Study, Collection, and Preservation. Universal Publishers, Inc., Boca Raton, Florida, i - xii, 445 pp.","Haszprunar, G. (2008) Monoplacophora (Tryblidia). pp. 97 - 104. In: Ponder, W. F. & Lindberg, D. R. (eds) Phylogeny and Evolution of the Mollusca, University of California Press, Berkeley, Los Angeles, London, i - xii, 1 - 469."]}

Monoplacophorus zenkevitchi Moskalev, Starobogatov & Filatova, 1983 Monoplacophorus zenkevitchi Moskalev, Starobogatov & Filatova 1983: 993, figs 5, 11��� 13. The species is known from the holotype only, described from the Central Pacific, north of Johnston Islands, west of Hawaii (20 �� 41.7 'N, 170 �� 52.9 'W) from 2000 m depth. However, the first record of the species dates back to Filatova et al. (1968), who mentioned it as undetermined Monoplacophora. Genus Neopilina Lemche, 1957 Type species: Neopilina galatheae Lemche, 1957, by monotypy., Published as part of Schwabe, Enrico, 2008, A summary of reports of abyssal and hadal Monoplacophora and Polyplacophora (Mollusca) *, pp. 205-222 in Zootaxa 1866 on page 207, DOI: 10.5281/zenodo.183815, {"references":["Moskalev, L. I., Starobogatov, Y. I. & Filatova, Z. A. (1983) New data on the abyssal Monoplacophora from the Pacific and South Atlantic Oceans. Zoologiceskij Zurnal, 62 (7), 981 - 996.","Lemche, H. (1957) A new living deep-sea mollusc of the Cambro-Devonian class Monoplacophora. Nature, 179, 413 - 416."]}

Vema bacescui (Menzies, 1968) Neopilina (Vema) bacescui Menzies 1968: 2, figs 1 a, 2 A���C, 3. The holotype of this rather large species (28 mm) was collected in the southeastern Pacific, Milne Edwards Deep of the Peru��Chile Trench (08�� 44 'S, 80 �� 45 'W), at a depth of 5986���6134 m., Published as part of Schwabe, Enrico, 2008, A summary of reports of abyssal and hadal Monoplacophora and Polyplacophora (Mollusca) *, pp. 205-222 in Zootaxa 1866 on page 209, DOI: 10.5281/zenodo.183815, {"references":["Menzies, R. J. (1968) New species of Neopilina of the Cambro-Devonian class Monoplacophora from the Milne- Edwards deep of the Peru-Chile Trench, R / V Anton Bruun. Marine Biological Association of India, Proceedings of the Symposium on Mollusca, 1, 1 - 9."]}

Neopilina galatheae Lemche, 1957 (Fig. 1 A) Neopilina galatheae Lemche 1957: 414, figs 1���4. Due to the presence of 10 specimens from the type locality: East Pacific, off Costa Rica (09�� 23 'N, 89 �� 32 'W), 3590 m, the first record of a living representative of the monoplacophora was not only a sensation but also led to numerous detailed studies of the morphology and anatomy of this representative of an ancient lineage. Later the species was recollected in abyssal depths from the following localities: �� specimen number unknown; 3000 km further north of the tip of the southern end of Baja California, 2780���2810 m [it remains unclear whether the author refers to N. galatheae or only to Neopilina sp.] (Wolff 1961) �� 3 specimens from Mexico, Baja California, off Cape San Lucas (22 �� 32.5 'N, 109 �� 40.8 'W), 2781���2809 m (Parker 1961) �� 1 specimen from the East Pacific, off Costa Rica (10 ��07'N, 89 �� 50 'W), 3718 m (Menzies & Layton 1962) �� 1 specimen (mentioned as ��� Neopilina aff. Galatheae ���) from the southeastern Pacific, off Chile (05�� 51.7 'S, 81 �� 48.8 'W), 5300���5320 m (Moskalev 1977)., Published as part of Schwabe, Enrico, 2008, A summary of reports of abyssal and hadal Monoplacophora and Polyplacophora (Mollusca) *, pp. 205-222 in Zootaxa 1866 on page 208, DOI: 10.5281/zenodo.183815, {"references":["Lemche, H. (1957) A new living deep-sea mollusc of the Cambro-Devonian class Monoplacophora. Nature, 179, 413 - 416.","Wolff, T. (1961) Animal life from a single abyssal trawling. Galathea 2 Report, 5, 129 - 162, pl. 9.","Parker, R. H. (1961) Speculations on the origin of the invertebrate faunas of the lower continental slope. Deep Sea Research, 8 (3 - 4), 286 - 293.","Menzies, R. J. & Layton, W. (1962) A new species of Monoplacophoran Mollusc, Neopilina (Neopilina) veleronis from the slope of the Cedros Trench, Mexico. Annals and Magazine of Natural History, 5 (13), 401 - 406, pls 7 - 10.","Moskalev, L. I. (1977) Towards a revision of molluscs Lepetidae (Gastropoda, Prosobranchia) of the world ocean. Works of the P. P. Shirshov Institute of Oceanology, Academy of Sciences U. S. S. R., 108, 52 - 78."]}