New species of the Genus Ochmazochiton (Mollusca, Polyplacophora) from the Lower Permian Reef Limestones of Shakhtau (Southern Cisuralia)

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Abstract

Eleven imprints of chiton valves from the Sakmara stage of the Shakhtau reef massif (Bashkir Cis-Urals) are assigned to a new species – Ochmazochiton uralensis sp. nov. Previously, the genus Ochmazochiton was known only from the type species described from the Lower and Middle Permian of Texas. Due to the unique preservation of the studied material, the structure of the pores of aesthetes is shown for the first time, and the structure of the insertion plates, the important morphological characters of the genus Ochmazochiton, the oldest representative of the oder Chitonida, is clarified.

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About the authors

А. V. Mazaev

Borissiak Paleontological Institute, Russian Academy of Sciences

Author for correspondence.
Email: mazaev.av@mail.ru
Russian Federation, Moscow, 117647

References

  1. Мазаев А.В. Новый вид рода Lekiskochiton (Mollusca, Polyplacophora) из нижнепермских рифогенных известняков Шахтау (Южное Приуралье) // Палеонтол. журн. 2024. № 3.
  2. Hoare R.D., Mapes R.H. Relationships of the Devonian Strobilepis and related Pennsylvanian problematica // Acta Palaeontol. Pol. 1995. V. 40. № 2. P. 111–128.
  3. Hoare R.D., Smith A.G. Permian Polyplacophora (Mollusca) from West Texas // J. Paleontol. 1984. V. 58. № 1. P. 82–103.
  4. Mazaev A.V. The rostroconch family Bransoniidae from the Early Permian Shakhtau Reef massif (Mollusca, Southern Cis-Urals) // Paleontol. J. 2023. V. 57. № 13.
  5. Schwabe E. Illustrated summary of chiton terminology (Mollusca, Polyplacophora) // Spixiana. 2010. V. 33. № 2. P. 171–194.
  6. Sirenko B.I. The importance of the development of articulamentum for taxonomy of chitons (Mollusca, Polyplacophora) // Ruthenica. 1997. V. 7. № 1. P. 1–24.
  7. Sirenko B.I. New Outlook on the System of Chitons (Mollusca: Polyplacophora) // Venus. 2006. V. 65. № 1-2. P. 27–49.
  8. Smith A.G., Hoare R.D. Paleozoic Polyplacophora: a checklist and bibliography // Occas. Pap. Calif. Acad. Sci. 1987. № 146. 71 p.

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2. Fig. 1. Ochmazochiton uralensis sp. nov., head shield, PIN paratype, No. 5538/10-1542: a – ventral surface impression, ×6: a1 – front view, a2 – top view, a3 – right view; b1, b2– latex impression of the ventral surface, ×6: bottom view and from behind; b – latex cast of the tegmentum, ×6: b1 – right view, b2 – top view, b3 – front view; d – latex cast of the insertion plate, ×20: g1 – right lateral edge, g2 – anterior edge, right part, g3 – anterior edge, left part, g4 – front edge, right side, bottom view; Bashkortostan, Shakhtau quarry, location No. 5538/10; the Sakmar tier. The scale is 1 mm.

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3. Fig. 2. Ochmazochiton uralensis sp. nov.: a – head shield, PIN paratype, No. 5538/10-1534, ×9 (except Fig. a7): a1–a3 – latex impression of the ventral surface: a1 – rear view, a2 – bottom view, a3 – oblique view; a4–a6 – ventral surface impression: a4 – left view, a5 – front view, a6 – top view; a7 – latex impression of a fragment of the tegmentum, large pores on the granules are clearly visible [front and left edge (up of the image), the position of the fragment on the print is shown by arrows in FIG. a6], ×15; b – PIN paratype, No. 5538/10-507, intermediate shield, ×4: b1 – latex impression of the ventral surface, bottom view; b2–b4 – latex impression of the dorsal surface: b2 – top view, b3 – rear view, b4 – left view; b5, b6 – ventral surface impression: left view, top view; b – PIN paratype, No. 5538/10-508, intermediate shield, ×4: b1 – latex impression of longitudinal cleavage of calcite biomorphosis along the tegmentum, prints of the bases of the apophyses are also observed; b2 – longitudinal cleavage of calcite biomorphosis along the tegmentum in the jugal and pleuro-lateral regions, as well as prints of the bases of the apophyses; Bashkortostan, Shakhtau quarry, location No. 5538/10; Sakmarsky tier. The scale is 1 mm.

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4. 3. Ochmazochiton uralensis sp. nov., intermediate shields of one animal: a – PIN paratype, No. 5538/10-1581: a1–a4 – latex impression: a1 – ventral surface, ×6; a2 – the right part of the ventral surface, including the insertion plate, ×15; a3 – ventral surface, oblique rear view, intravital lesion in the right part of the posterior margin, ×10; a4 – dorsal surface: insertion plate and fragment of apophysis, lateral area with thin sculptural elements, pleuro-lateral area – imprint of calcite biomorphosis according to tegmentum, ×6; a5, a6 – ventral surface imprint: right and top view, ×6; b – PIN paratype, No. 5538/10-1580, dorsal surface imprint: insertion plate and apophysis, lateral area imprint, in the pleural area calcite biomorphosis by tegmentum (selective substitution), ×6; Bashkortostan, Shakhtau quarry, location No. 5538/10; Sakmar tier. The scale is 1 mm.

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5. Fig. 4. Ochmazochiton uralensis sp. nov., PIN paratype, No. 5538/10-1549, latex impressions of the dorsal surface of the intermediate flap: a1, a2 – top view, photographs from different angles on a light and electron microscope, ×8; a3–a5 – front and rear view, ×8; b1, b2 – left insertion plate: oblique side view and top view, ×40; b1, b2 – sculptural elements of the tegmentum with the pores of aesthetes, as well as fragments of the articamentum, ×40: b1 – the right part of the shield, the lateral region and a fragment of the pleural region; b2 – the left part of the shield: the pleural region and a fragment of the lateral region, as well as the apophysis and insertion plate; Bashkortostan, Shakhtau quarry, location No. 5538/10; Sakmarsky tier. The scale is 1 mm.

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6. 5. Ochmazochiton uralensis sp. nov., holotype PIN, No. 5538/10-1533, tail shield: a1–a3 – ventral surface impression, ×8: a1 – rear view, a2 – right view, a3 – top view; b1–b3 – latex impression of the ventral surface, ×8: b1, b2 – bottom view (secondary electron detector, backscattered electron detector), dotted line shows reconstructions of the anterior edges of the tegmentum and apophyses, b3 – oblique view, arrows show insertion plates; b1–b4 – latex impression of the dorsal surface, ×8: b1 – right view, arrow shows insertion plate; b2 is the front view, the dotted line shows the reconstruction of the edge of the apophysis, b3 is the top view, the arrow shows the insertion plate, the dotted line shows the reconstruction of the edges of the apophyses, the black dots on the granules are microscopic air bubbles in latex; b4 is the back view; g1, g2 is a latex cast, a fragment of the ventral surface, the left insertion plate, ×40: g1 – bottom view, g2 – oblique side view; Bashkortostan, Shakhtau quarry, location No. 5538/10; Sakmarsky tier. The scale is 1 mm.

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