Ferreiraella populi Sigwart sp. nov. Ferreiraella sp. Chen et al. 2024: figs. 2 a, 2 b, 2 d and 3 v. Materials Type status: Holotype. Occurrence: catalogNumber: SMF 383139; recordedBy: Chong Chen; individualCount: 1; lifeStage: adult; occurrenceID: A8BDC46D-A6E3-5EF8-82D8-57663382AEA4; Taxon: scientificName: Ferrieraella populi; kingdom: Animalia; phylum: Mollusca; class: Polyplacophora; order: Lepidopleurida; family: Ferreiraellidae; genus: Ferreiraella; specificEpithet: populi; taxonRank: species; scientificNameAuthorship: Sigwart; nomenclaturalCode: ICZN; Location: higherGeography: Izu-Ogasawara Trench; country: Japan; verbatimLocality: Izu-Ogasawara Trench, West of KEO; verbatimDepth: 5506; minimumDepthInMeters: 5506; maximumDepthInMeters: 5506; verbatimCoordinates: 32°34.6760'N, 143°46.1235'E; verbatimLatitude: 32°34.6760'N; verbatimLongitude: 143°46.1235'E; decimalLatitude: 32.577933; decimalLongitude: 143.768725; Identification: identifiedBy: Juila Sigwart; dateIdentified: 2024; Event: samplingProtocol: suction sampler; eventDate: 2024-05; year: 2024; month: 5; habitat: woodfall; Record Level: language: en; institutionID: 16946ec1-8db3-45b8-b084-7644384cc5f5; basisOfRecord: PreservedSpecimen; Material Entity: associatedSequences: https://www.ncbi.nlm.nih.gov/nuccore/PX804841 Type status: Paratype. Occurrence: catalogNumber: SMF 383138; recordedBy: Chong Chen; individualCount: 1; lifeStage: adult; occurrenceID: 0567F91E-526E-5EC1-BBE8-BAC13E40468D; Taxon: scientificName: Ferrieraella populi; kingdom: Animalia; phylum: Mollusca; class: Polyplacophora; order: Lepidopleurida; family: Ferreiraellidae; genus: Ferreiraella; specificEpithet: populi; taxonRank: species; scientificNameAuthorship: Sigwart; nomenclaturalCode: ICZN; Location: higherGeography: Izu-Ogasawara Trench; country: Japan; verbatimLocality: Izu-Ogasawara Trench, West of KEO; verbatimDepth: 5506; minimumDepthInMeters: 5506; maximumDepthInMeters: 5506; verbatimCoordinates: 32°34.6760'N, 143°46.1235'E; verbatimLatitude: 32°34.6760'N; verbatimLongitude: 143°46.1235'E; decimalLatitude: 32.577933; decimalLongitude: 143.768725; Identification: identifiedBy: Juila Sigwart; dateIdentified: 2024; Event: samplingProtocol: suction sampler; eventDate: 2024-05; year: 2024; month: 5; habitat: woodfall; Record Level: language: en; institutionID: 16946ec1-8db3-45b8-b084-7644384cc5f5; basisOfRecord: PreservedSpecimen Type status: Paratype. Occurrence: catalogNumber: SMF 383140; recordedBy: Chong Chen; individualCount: 1; lifeStage: adult; occurrenceID: 386AD89A-1A96-5946-A45C-0CB0E195EA10; Taxon: scientificName: Ferrieraella populi; kingdom: Animalia; phylum: Mollusca; class: Polyplacophora; order: Lepidopleurida; family: Ferreiraellidae; genus: Ferreiraella; specificEpithet: populi; taxonRank: species; scientificNameAuthorship: Sigwart; nomenclaturalCode: ICZN; Location: higherGeography: Izu-Ogasawara Trench; country: Japan; verbatimLocality: Izu-Ogasawara Trench, West of KEO; verbatimDepth: 5506; minimumDepthInMeters: 5506; maximumDepthInMeters: 5506; verbatimCoordinates: 32°34.6760'N, 143°46.1235'E; verbatimLatitude: 32°34.6760'N; verbatimLongitude: 143°46.1235'E; decimalLatitude: 32.577933; decimalLongitude: 143.768725; Identification: identifiedBy: Juila Sigwart; dateIdentified: 2024; Event: samplingProtocol: suction sampler; eventDate: 2024-05; year: 2024; month: 5; habitat: woodfall; Record Level: language: en; institutionID: 16946ec1-8db3-45b8-b084-7644384cc5f5; basisOfRecord: PreservedSpecimen Type status: Paratype. Occurrence: catalogNumber: SMF 383141; recordedBy: Chong Chen; individualCount: 1; lifeStage: adult; occurrenceID: 752C0E55-09AE-5399-9EF4-83381C60D4A4; Taxon: scientificName: Ferrieraella populi; kingdom: Animalia; phylum: Mollusca; class: Polyplacophora; order: Lepidopleurida; family: Ferreiraellidae; genus: Ferreiraella; specificEpithet: populi; taxonRank: species; scientificNameAuthorship: Sigwart; nomenclaturalCode: ICZN; Location: higherGeography: Izu-Ogasawara Trench; country: Japan; verbatimLocality: Izu-Ogasawara Trench, West of KEO; verbatimDepth: 5506; minimumDepthInMeters: 5506; maximumDepthInMeters: 5506; verbatimCoordinates: 32°34.6760'N, 143°46.1235'E; verbatimLatitude: 32°34.6760'N; verbatimLongitude: 143°46.1235'E; decimalLatitude: 32.577933; decimalLongitude: 143.768725; Identification: identifiedBy: Juila Sigwart; dateIdentified: 2024; Event: samplingProtocol: suction sampler; eventDate: 2024-05; year: 2024; month: 5; habitat: woodfall; Record Level: language: en; institutionID: 16946ec1-8db3-45b8-b084-7644384cc5f5; basisOfRecord: PreservedSpecimen Type status: Paratype. Occurrence: catalogNumber: SMF 383142; recordedBy: Chong Chen; individualCount: 1; lifeStage: adult; occurrenceID: 8B3FC026-68C4-580F-ABC1-34463B13C036; Taxon: scientificName: Ferrieraella populi; kingdom: Animalia; phylum: Mollusca; class: Polyplacophora; order: Lepidopleurida; family: Ferreiraellidae; genus: Ferreiraella; specificEpithet: populi; taxonRank: species; scientificNameAuthorship: Sigwart; nomenclaturalCode: ICZN; Location: higherGeography: Izu-Ogasawara Trench; country: Japan; verbatimLocality: Izu-Ogasawara Trench, West of KEO; verbatimDepth: 5506; minimumDepthInMeters: 5506; maximumDepthInMeters: 5506; verbatimCoordinates: 32°34.6760'N, 143°46.1235'E; verbatimLatitude: 32°34.6760'N; verbatimLongitude: 143°46.1235'E; decimalLatitude: 32.577933; decimalLongitude: 143.768725; Identification: identifiedBy: Juila Sigwart; dateIdentified: 2024; Event: samplingProtocol: suction sampler; eventDate: 2024-05; year: 2024; month: 5; habitat: woodfall; Record Level: language: en; institutionID: 16946ec1-8db3-45b8-b084-7644384cc5f5; basisOfRecord: PreservedSpecimen Type status: Paratype. Occurrence: catalogNumber: SMF 383143; recordedBy: Chong Chen; individualCount: 1; lifeStage: adult; occurrenceID: 830CF36E-7701-5652-98FD-764093FFFD0C; Taxon: scientificName: Ferrieraella populi; kingdom: Animalia; phylum: Mollusca; class: Polyplacophora; order: Lepidopleurida; family: Ferreiraellidae; genus: Ferreiraella; specificEpithet: populi; taxonRank: species; scientificNameAuthorship: Sigwart; nomenclaturalCode: ICZN; Location: higherGeography: Izu-Ogasawara Trench; country: Japan; verbatimLocality: Izu-Ogasawara Trench, West of KEO; verbatimDepth: 5506; minimumDepthInMeters: 5506; maximumDepthInMeters: 5506; verbatimCoordinates: 32°34.6760'N, 143°46.1235'E; verbatimLatitude: 32°34.6760'N; verbatimLongitude: 143°46.1235'E; decimalLatitude: 32.577933; decimalLongitude: 143.768725; Identification: identifiedBy: Juila Sigwart; dateIdentified: 2024; Event: samplingProtocol: suction sampler; eventDate: 2024-05; year: 2024; month: 5; habitat: woodfall; Record Level: language: en; institutionID: 16946ec1-8db3-45b8-b084-7644384cc5f5; basisOfRecord: PreservedSpecimen Type status: Paratype. Occurrence: catalogNumber: SMF 383144; recordedBy: Chong Chen; individualCount: 1; lifeStage: adult; occurrenceID: BE0766CA-8BAE-5F9C-A62D-2E724051E8B1; Taxon: scientificName: Ferrieraella populi; kingdom: Animalia; phylum: Mollusca; class: Polyplacophora; order: Lepidopleurida; family: Ferreiraellidae; genus: Ferreiraella; specificEpithet: populi; taxonRank: species; scientificNameAuthorship: Sigwart; nomenclaturalCode: ICZN; Location: higherGeography: Izu-Ogasawara Trench; country: Japan; verbatimLocality: Izu-Ogasawara Trench, West of KEO; verbatimDepth: 5506; minimumDepthInMeters: 5506; maximumDepthInMeters: 5506; verbatimCoordinates: 32°34.6760'N, 143°46.1235'E; verbatimLatitude: 32°34.6760'N; verbatimLongitude: 143°46.1235'E; decimalLatitude: 32.577933; decimalLongitude: 143.768725; Identification: identifiedBy: Juila Sigwart; dateIdentified: 2024; Event: samplingProtocol: suction sampler; eventDate: 2024-05; year: 2024; month: 5; habitat: woodfall; Record Level: language: en; institutionID: 16946ec1-8db3-45b8-b084-7644384cc5f5; basisOfRecord: PreservedSpecimen Type status: Paratype. Occurrence: catalogNumber: NSMT-Mo 79868; recordedBy: Chong Chen; individualCount: 1; lifeStage: adult; occurrenceID: 34B3141A-0824-520A-ACD9-7E9BD4236BB2; Taxon: scientificName: Ferrieraella populi; kingdom: Animalia; phylum: Mollusca; class: Polyplacophora; order: Lepidopleurida; family: Ferreiraellidae; genus: Ferreiraella; specificEpithet: populi; taxonRank: species; scientificNameAuthorship: Sigwart; nomenclaturalCode: ICZN; Location: higherGeography: Izu-Ogasawara Trench; country: Japan; verbatimLocality: Izu-Ogasawara Trench, West of KEO; verbatimDepth: 5506; minimumDepthInMeters: 5506; maximumDepthInMeters: 5506; verbatimCoordinates: 32°34.6760'N, 143°46.1235'E; verbatimLatitude: 32°34.6760'N; verbatimLongitude: 143°46.1235'E; decimalLatitude: 32.577933; decimalLongitude: 143.768725; Identification: identifiedBy: Juila Sigwart; dateIdentified: 2024; Event: samplingProtocol: suction sampler; eventDate: 2024-05; year: 2024; month: 5; habitat: woodfall; Record Level: language: en; institutionID: d08b12cb-dc48-4de3-b08a-47ea57591abe; basisOfRecord: PreservedSpecimen Type status: Paratype. Occurrence: catalogNumber: NSMT-Mo 79869; recordedBy: Chong Chen; individualCount: 1; lifeStage: adult; occurrenceID: 738029B9-DFC8-5ACE-A76B-8831E2718B1F; Taxon: scientificName: Ferrieraella populi; kingdom: Animalia; phylum: Mollusca; class: Polyplacophora; order: Lepidopleurida; family: Ferreiraellidae; genus: Ferreiraella; specificEpithet: populi; taxonRank: species; scientificNameAuthorship: Sigwart; nomenclaturalCode: ICZN; Location: higherGeography: Izu-Ogasawara Trench; country: Japan; verbatimLocality: Izu-Ogasawara Trench, West of KEO; verbatimDepth: 5506; minimumDepthInMeters: 5506; maximumDepthInMeters: 5506; verbatimCoordinates: 32°34.6760'N, 143°46.1235'E; verbatimLatitude: 32°34.6760'N; verbatimLongitude: 143°46.1235'E; decimalLatitude: 32.577933; decimalLongitude: 143.768725; Identification: identifiedBy: Juila Sigwart; dateIdentified: 2024; Event: samplingProtocol: suction sampler; eventDate: 2024-05; year: 2024; month: 5; habitat: woodfall; Record Level: language: en; institutionID: d08b12cb-dc48-4de3-b08a-47ea57591abe; basisOfRecord: PreservedSpecimen Description Holotype 17 × 9.5 mm, oval. Overall colour of valves cream, off-white, marked with black spots of mineral deposits on valve diagonal. Valves rounded, not elevated (dorsal elevation ratio nearly flat in valve III, Fig. 1 A). Head valve semicircular. Intermediate valves rectangular, lateral margins rounded but relatively straight, anterior margin slightly convex, posterior margin paralleling anterior margin, apex not projecting. Lateral areas slightly raised, aligned with posterior edge of underlying apophysis, visible from contrasting mineral deposits that are mainly seen on either side of the diagonal. Tail valve smaller than head valve, flattened, mucro central, posterior slope flat but margin slightly crenulate (Fig. 1 A and B). Tegmentum smooth, covered with thin tissue and minor apical projections from aesthete pores. Aesthetes irregularly arranged in bundles of 1 megalaesthete and approximately 2 micraesthetes (Fig. 2 A and D). Aesthete bundles typically widely separated with macraesthete anterior and two micraesthetes trailing to posterior. Articulamentum white, well developed, without insertion plate or callus, apophyses moderately narrow, triangular in the intermediate valves and tail valve. Jugal sinus wide. Central tooth of radula small, bud-like, first (inner) lateral teeth with compact brush-like projections (Fig. 2 A and B). Second (major) lateral teeth with flattened, tridentate mineralised cusps. Major uncinal (sweeper) teeth broad, spoon-shaped, but comb-like blade, similar in width and height to major lateral teeth (Fig. 2 C). Radula of the holotype measured 6.1 mm with 53 rows of fully mineralised teeth. Girdle very wide, dorsally densely covered with oblong spicule-scale, only one type observed, but longer towards the valve interstices (80-120 × 20-25 μm). Scales distally pointed, without sculpture, smooth, but rough in texture, oval in cross section (Fig. 2 E). Ventral side of girdle naked. Gills 18-20 on each side (18 in holotype SMF 383139; 20 in paratype SMF 383138), smaller to the anterior, extending from valve V to the anus. Schwabe organ not visible. Diagnosis Animal medium, type specimens up to approximately 25 mm long. Overall colour off-white. Shell rounded, valves not beaked, mucro of tail valve central and not raised; tail valve smaller than head valve. Tegmentum smooth; aesthetes in irregular bundles of 1 megalaesthete and 2 micraesthetes, with protruding caps. Girdle densely covered with oblong spicule-scales. Major lateral teeth of radula with relatively flattened, tridentate cusps. Major uncinus comb-like, not higher than the major lateral. Eighteen to twenty gills on each side. Etymology Species epithet " populi ", Latin singular noun in the genetive case, meaning " of the people ". This name was suggested 11 different times from over 8,000 total contributions to the public naming competition. Distribution Only known from the type locality, woodfall on the abyssal plain in the Northwestern Pacific, about 150 km east of the Ogasawara Trench axis, off Japan, 32°34.6760N, 143°46.1235E, 5506 m depth. Ecology Endemic to sunken wood. Type material Type specimens are deposited at the Senckenberg Research Institute and Natural History Museum Frankfurt, Germany and the National Museum of Nature and Science, Japan. Holotype (SMF 383139) partially disarticulated, consisting of mounts of shell, perinotum and radula, originally fixed in formalin; paratype 1 used for DNA barcoding (SMF 383142), three additional paratypes originally preserved in 99 % ethanol (SMF 383143, SMF 383144, NSMT-Mo 79868), four paratypes originally fixed in formalin (NSMT-Mo 79869, SMF 383138, SMF 383140, SMF 383141). Notes Molecular data are available only for two other species in this genus, and the COI barcode region from the new species (GenBank accession number PX 804841) is only 88 % identical with Ferreiraella plana (GenBank accession number HQ 907844) and 87 % identical with F. xylophaga karenae (GenBank accession numbers HQ 907845, HQ 907846) based on BLAST comparison (https://blast.ncbi.nlm.nih.gov/). The new species can be distinguished from all other members of the genus by its unusually small tail valve, and having aesthetes with fewer pores in a bundle and with bundles that are unusually stretched with longer separation between a macraesthete and corresponding micraesthetes. The new species has the distinctive comb-form major uncinus “ sweeper ” teeth that are diagnostic for Ferreiraella, but they are less enlarged in the new species than other members of the genus. The compact, brush-tipped inner lateral teeth are also described from other members of the genus and here are apparently soft and complex, as the dehydrated teeth form a cap like a morel. The new species is most similar in superficial appearance to F. tsuchidai Saito, 2006, which occurs at similar depth (type locality 5567 m) in the Philippine Basin, in terms of the valve shape and elevation. Specimens of F. tsuchidai and F. charazata Sigwart, 2025 (Senckenberg Ocean Species Alliance (SOSA) et al. 2025), like the new species, have been observed to frequently host epibiotic serpulid tubeworms on their tail valves (Saito 2006, Senckenberg Ocean Species Alliance (SOSA) et al. 2025). The new species represents the third species of Ferreiraella found in Japan, after F. takii (Wu & Okutani, 1984) and F. soyomaruae (Wu & Okutani, 1984) were described from shallower depths of 1250 m (F. takii) and 3100 m (F. soyomaruae), and the new species is more closely similar to F. takii. Ferreiraella takii differs from the new species in its valve shape, with more convex anterior margin of the intermediate valves compared to straighter in the new species, and the size of the tail valves, which is distinctly smaller than the head valve in the new species, whereas F. takii has head and tail valve of about the same size. Interestingly, the radula is also different, with a shorter radula (5.5 mm in F. takii) with apparently denser arrangement of teeth in F. takii (over 54 rows of teeth in the new species, but 68 rows in a shorter radula in F. takii (Wu and Okutani 1984). Finally, F. takii has several types of girdle spicules, where only one was observed in the new species. Paratype 1 (SMF 383142) of the new species shows a valve teratology on valve VII (Fig. 1 E) with the valve split on the mid-line and growing in two slightly separated segments. Valve splitting has been observed in other species, although not frequently (Dell'Angelo and Schwabe 2010) and has been described with tomographic reconstruction in the shallow water species Acanthopleura granulata (Gmelin, 1791) (Kingston et al. 2019). Deep sea deposits of sunken wood provide habitat for diverse chitons species including two endemic families, Nierstraszellidae and Ferreiraellidae. Evidence from gut-associated bacteria in other wood-endemic chitons indicates that they are secondary consumers, not directly feeding on the wood (Duperron et al. 2012), but this has never been tested for Ferreiraella.

Published as part of (SOSA), Senckenberg Ocean Species Alliance, Chen, Chong, Frank, Hosea, Kraniotis, Laura, Nakadera, Yumi, Schwabe, Enrico, Sigwart, Julia D., Trautwein, Bianca & Vončina, Katarzyna, 2026, Ocean Species Discoveries 28 – 30 — new species of chitons (Mollusca, Polyplacophora) and a public naming competition, pp. e 180491 in Biodiversity Data Journal 14 on page e180491, DOI: 10.3897/BDJ.14.e180491