Placiphorella granulosa Voncina 2026, sp. nov.

Placiphorella granulosa Vončina sp. nov. Materials Type status: Holotype. Occurrence: catalogNumber: MNHN-IM-2019-34864; recordedBy: leg. Samadi and Corbari; individualCount: 1; lifeStage: adult; occurrenceID: 6AC81AF3-7B6E-5CB1-87C0-7FDB7C2D4E30; Taxon: scientificName: Placiphorella granulosa Vončina; kingdom: Animalia; phylum: Mollusca; class: Polyplacophora; order: Chitonida; family: Mopaliidae; genus: Placiphorella; specificEpithet: granulosa; taxonRank: species; scientificNameAuthorship: Vončina; nomenclaturalCode: ICZN; Location: higherGeography: Pacific Ocean; country: Papua New Guinea; locality: Papua New Guinea, Vitiaz Strait; minimumDepthInMeters: 860; maximumDepthInMeters: 880; verbatimLatitude: 05°59'S; verbatimLongitude: 147°39'E; Identification: identifiedBy: Katarzyna Vončina; dateIdentified: 2024; Event: eventDate: 2010-10 - 07; eventRemarks: Expedition: BIOPAPUA, Station: CP 3724, Ship: Alis; Record Level: language: en; basisOfRecord: PreservedSpecimen; Material Entity: associatedSequences: https://www.ncbi.nlm.nih.gov/nuccore/PX804842 Type status: Paratype. Occurrence: catalogNumber: SMF 383080; recordedBy: leg. Samadi and Corbari; individualCount: 1; lifeStage: adult; otherCatalogNumbers: MNHN-IM-2019-35216; occurrenceID: 2806D9FE-C85C-5A12-B42A-3CACAD7E87A5; Taxon: scientificName: Placiphorella granulosa Vončina; kingdom: Animalia; phylum: Mollusca; class: Polyplacophora; order: Chitonida; family: Mopaliidae; genus: Placiphorella; specificEpithet: granulosa; taxonRank: species; scientificNameAuthorship: Vončina; nomenclaturalCode: ICZN; Location: higherGeography: Pacific Ocean; country: Papua New Guinea; locality: Papua New Guinea, Vitiaz Strait; minimumDepthInMeters: 860; maximumDepthInMeters: 880; verbatimLatitude: 05°59'S; verbatimLongitude: 147°39'E; Identification: identifiedBy: Katarzyna Vončina; dateIdentified: 2024; Event: eventDate: 2010-10 - 07; eventRemarks: Expedition: BIOPAPUA, Station: CP 3724, Ship: Alis; Record Level: language: en; basisOfRecord: PreservedSpecimen Description Body of medium size (holotype MNHN-IM-2019-34864: 18 x 15 mm, paratype SMF 383080: ca. 19.5 x 16 mm – specimen curled up; both specimens measured from the ventral side), broadly oval, subcarinated, moderately elevated (valve elevation = 0.35), side slopes straight; valves solid, not beaked or with small, not pronounced apex (Fig. 5). Tegmentum densely granulated, white-yellow or brown; girdle broadly expanded anteriorly, light-brown with white patches (Fig. 5). Head valve crescent-shaped, front slope concave, posterior margin very widely V-shaped, with a small median notch, tegmentum granulated, some inconspicuous concentric growth lines (Figs 5, 6 A). Intermediate valves broadly rectangular, much wider than long, front margin almost straight, weakly projected forward at jugal part; side margins rounded, hind margin straight to weakly convex, apex weakly indicated, tegmentum granulated, lateral areas raised, bordered by weakly indicated diagonal ribs (Figs 5, 6 B). Tail valve small, roughly trapezoidal in outline, with front margin concave and rounded posterior margin, mucro raised, terminal, overhanging, antemucronal area straight, postmucronal area convex, tegmentum granulated with two ribs separating the ante- and postmucronal areas (Figs 5, 6 C). Articulamentum strongly developed, white, valves calloused, apophyses very wide, short, slightly rounded to subtrapezoidal, paralleled in the tail valve, separated by a jugal sinus, insertion plates short, slit formula 19 / 1 / sinus, slits shallow, no slit rays, teeth thick, bilobed and crenulated (Fig. 5 C-I). Girdle broadly expanded anteriorly, uniformly brown or yellowish, dorsally covered with two kinds of spicules: short, single, densely arranged, smooth, and (mostly) mamillated spicules, L: 80–121 μm (mean = 106 μm, n = 7), W: 42–49 μm (mean = 45, n = 7), and longer, smooth and sharply-pointed spicules clustered in groups of a few, L: 241–313 μm (mean = 272 μm, n = 3), W: 28–35 μm (mean = 32 μm, n = 3) (Fig. 7 A and C). Large bristles only present near the girdle margin and not prominent, beset with slender, smooth and sharply-pointed spicules, L: 240–280 μm (mean = 240 μm, n = 2), W: 30–40 μm (mean = 35 μm, n = 2), arranged in oblique series along axis (Fig. 7 B). Marginal fringe composed of two kinds of spicules: straight, slightly striated (sometimes smooth), sharp-topped spicules, L: 129–152 μm (mean = 137 μm, n = 3), W: 25–30 μm (mean = 27 μm, n = 3), and second kind located closer to the ventral side: shorter and flattened, ovate spicules (Fig. 7 D). Hyponotum covered in short, lanceolate-shaped, striated in the anterior half, sharply-pointed spicules; usually clustered in groups in the anterior half of the girdle, individually distributed in the posterior half, L: 50–82 μm (mean = 73, n = 6), W: 18–21 μm (mean = 20, n = 6) (Fig. 7 E). Spicules of precephalic tentacles composed of two kinds of spicules: short, ovate-shaped, L: 47–64 μm (mean = 54, n = 8), W: 12–24 μm (mean = 19, n = 8), and long, lanceolate, smooth, which often cluster together and form a bristle similar to the dorsal ones, ca. 100 x 20 μm (Fig. 7 F). Radula of holotype small, ca. 4.5 mm in length in holotype, with 48 rows of teeth, of which 40 are of mature. Central tooth subtrapezoidal, with wide base and curved blade, first lateral tooth elongate, major lateral tooth with tricuspid head, denticles pointed, central denticle somewhat longer than others, outer denticle widest and shallowest notched (Fig. 6 D). Gills merobranchial, 11–13 ctenidia per side (12 and 13 on the left and right side, respectively, in holotype, 11 in paratype). Paratype morphology mostly identical with holotype. Front margin of intermediate and tail valves stronger projected forward at jugal part, slits in head valve: 23, 30 incisions due to the irregular splitting. Smaller number of mamillated spicules on dorsum. Diagnosis Animal medium-sized, body broadly oval, valves subcarinated and moderately elevated, not beaked, tegmentum densely granulose. Tail valve roughly trapezoidal in shape, mucro terminal, raised and overhanging. Girdle expanded anteriorly, perinotum covered with two kinds of spicules: single, smooth, and (mostly) mamillated spicules, and longer, smooth and sharply-pointed spicules clustered in groups of a few; sparsely scattered large bristles beset with elongated slender spicules; hyponotum covered in short, lanceolate-shaped, striated in the anterior half, sharply-pointed spicules. Etymology The specific epithet granulosa is a feminine adjective formed from the Latin noun granulum = small grain, and the suffix - osa = “ full of ” highlighting the granular surface of the tegmentum characteristic of the new species. Distribution At present known only from its type locality, Papua New Guinea, Vitiaz Strait, western Pacific Ocean, at 05°59′S, 147°39′E, collected at 860–880 m depth. Type material Holotype (MNHN-IM-2019-34864) now partly disarticulated: mounts of shells (valves I, VII, VIII) and parts of girdle and radula mounted on three SEM stubs, respectively, and the vial with the specimen stored in 96 % ethanol; one paratype (SMF 383080) now partly disarticulated: mounts of shells (valves I, II, VIII), and the vial with the specimen stored in 96 % ethanol. Differential Diagnosis There are fifteen currently accepted species of Placiphorella, and six closely resemble Placiphorella granulosa sp. nov. by having number of slits in a head valve> 12 and granular tegmentum. It can be differentiated from: Placiphorella albitestae Taki, 1954 by the more densely arranged, prominent, round granules, not thickened posterior margin of a head valve (vs. thickened to an obvious ridge in P. albitestae), and straight antemucronal slope (vs. concave in P. albitestae) (Taki 1954). Placiphorella atlantica (A. E. Verrill & S. Smith, 1882) by terminal and overhanging mucro (vs. mucro subterminal in P. atlantica), longer spicules of the girdle (80-121 x 42-49 µm, smooth spicules, subtly mamillated in P. granulosa sp. nov. vs. 70-80 x 22-30 µm, striated with sharp beak on top in P. atlantica), striated ventral spicules (vs. smooth in P. atlantica) (Verrill 1882). Placiphorella laurae Clark, 2019 by the trapezoidal shape of the tail valve (vs. broadly triangular, pointed in P. laurae), absence of radial sulci on head valve (vs. eight conspicuous sulci in P. laurae) (Clark 2019). Placiphorella methanophila Vončina, 2024 by the shape of the VII valve (front margin almost straight and hind margin straight to weakly convex in P. granulosa sp. nov. vs. front margin widely angular and hind margin concave), roughly rectangular shape of the tail valve (vs. much wider, angular in P. methanophila), oblong and mamillated spicules of the perinotum (vs. single dorsal spicules sharply pointed in P. methanophila) (Senckenberg Ocean Species Alliance (SOSA) et al. 2024). Placiphorella isaotakii Saito, Fujikura & Tsuchida, 2008 by the spicules of hyponotum (lanceolate-shaped, striated in the anterior half, sharply-pointed spicules up to 82 x 20 µm in P. granulosa sp. nov. vs. obtuse, smooth spicules up to 180 × 30 µm in P. isaotakii) (Saito et al. 2008). Placiphorella okutanii Saito, Fujikura & Tsuchida, 2008 by the shorter and thicker spicules of perinotum (up to 121 x 49 μm vs. 150 x 30 µm in P. okutanii), the spicules of hyponotum (short, lanceolate-shaped, striated in the anterior half, sharply-pointed spicules in P. granulosa sp. nov. vs. obtusely pointed, smooth spicules in P. okutanii). Notes The obtained mitochondrial cytochrome oxidase subunit 1 (COI) gene sequence (GenBank accession number PX 804842) was positively checked as belonging to Placiphorella against the GenBank database. The closest matches were sequences of P. atlantica with similarity of 94.48 % (GU 806116.1) or 94.39 % (GU 806076.1). The ranges of uncorrected genetic p-distances between P. granulosa sp. nov. and all other Placiphorella sequences available