Published September 2, 2014 | Version v1
Taxonomic treatment Open

Mesosaccella rogovi Hryniewicz & Little & Nakrem 2014, sp. nov.

Description

Mesosaccella rogovi sp. nov.

(Figures 5 R–T, 7 A–F)

2011 Malletiid sp. 1—Hammer et al., fig. 7n–o, tab. 2.

Etymology. After Mikhail A. Rogov, Russian palaeontologist specializing in Jurassic stratigraphy of the Arctic.

Type locality. Seep 9, Knorringfjellet, Spitsbergen, 78°18’49.9”N 16°10’58.9”E.

Type material. Holotype: PMO 224.971; a well preserved left valve showing the shape and characteristic ornament of posterodorsal margin. Paratypes: PMO 217.229; a partially preserved articulated internal mould showing anterior adductor muscle scar, posterior adductor muscle scar and weak pallial line. PMO 217.371; a well preserved articulated internal mould with fragments of shell, which shows weak ridges formed by growth line deflections, a carina and lancet-shaped escutcheon; the mould shows the pallial line and weak imprints of the external ridges. PMO 217.539; a partial right valve with cardinal area showing continuous tooth row.

Material examined. 89 specimens, mostly articulated valves or internal moulds with portions of the shell remaining. See Appendix 1 for the list of specimens.

Diagnosis. Elongated, lancet-shaped species with posterior part more than four times the length of the anterior part. Up to three weak posterior ridges formed by growth line deflections on the posterior part of the shell. A carina subparallel to the posterodorsal margin runs from the umbo to the posterior shell extremity.

Dimensions. 3.5–23 mm in length, 1.2–9.1 mm in height, 1–8.2 mm in width. See Figure 8 A–D and Appendix 2D for details.

Description. Medium to large, up to 23 mm long, 9.1 mm high and 8.2 mm wide, elongated (H/L≈0.42), lancet-shaped, weakly inflated (W/L≈0.32, W/H≈0.77); greatest height and width around medial plane. Elongated shape especially well expressed in posterior part, which occupies around 80% of total length (Pl/L≈0.79). Shell shape parameters remain relatively constant throughout ontogeny. External ornament of narrowly-spaced, commarginal growth lines, strongest in median part of shell and weaker towards both anterior and posterior. Towards posterior, disappearance of concentric ridges marked by up to three closely spaced ridges composed of series of growth line deflections. A single carina runs subparallel to posterodorsal margin. Escutcheon shallow, pointed anteriorly, presumably lancet-shaped. Anterodorsal margin straight to weakly convex, without well demarcated lunule. Anterior margin rounded to blunt. Anteroventral margin rounded, passing into weakly rounded ventral margin. Ventral margin passes into weakly convex posteroventral margin. Posterior end pointed, dorsally sloping and passing into long, posterodorsal margin; parallel to dorsal carina. Beaks prosogyrate. Dentition taxodont, teeth orthomorphodont. Anterior and posterior teeth rows meet below umbo. Posterior teeth much smaller than anterior teeth. Specimen 20 mm long has up to 38 teeth in posterior row and ca. 11 teeth in anterior row. Anterior adductor muscle scar small, rounded. Posterior adductor muscle scar elongated, more impressed anteriorly, progressively fading towards posterior. In some specimens weak elongated muscle scars of uncertain origin visible along dorsal margin. Pallial line weakly impressed, parallel to commissure; pallial sinus very shallow to absent, and weakly impressed.

Remarks. Mesosaccella rogovi differs from M. morrisi (Deshayes, 1853) in being more elongated, having stronger commarginal ornament and, in addition, showing a weak dorsal carina and growth line deflections in the posterior shell areas (cf. Duff 1978). Mesosaccella elliptica (Goldfuss, 1837) has a shape closer to M. rogovi, but it lacks the distinctive commarginal ornament deflections in the posterior part of the shell and the dorsal carina (Hodges 2000). Mesosaccella choroschovensis (Borissjak, 1904) is much shorter and more oval than M. rogovi, with a gently rounded posterior end and lacks the ridges of M. rogovi. Leda striatula Forbes, 1845, has a similar growth line deflection to M. rogovi in the posterior area. However, it is both less elongated and has a stronger carina than M. rogovi . Mesosaccella rogovi is as elongated as both M. grovei (Lartet, 1872) and M. larteti Chavan, 1947, but it is more inequilateral than the former and has much weaker commarginal ornament than the latter.

Occurrence. Seeps 1, 2, 3, 5, 8, 9, 12, 13 and 15 (Upper Volgian–uppermost Ryazanian), Slottsmøya Member, Svalbard (Tab. 1).

Palaeoecology. Mesosaccella rogovi was probably a shallow burrower, like other protobranch bivalves (Stanley 1970; Sanders & Allen 1985; Zardus 2002). The elongated and streamlined shell indicates it was an efficient burrower, and the very shallow pallial sinus implies the presence of a short siphon, developed either for respiration or for feeding from the sediment-water interface (e.g. Hodges 2000, text-fig. 32). Some protobranchs inhabiting modern vent and seep environments are believed to benefit from the concentration of chemosynthetically produced organic matter in the sediments, and possibly even feed on bacterial mats (e.g. Allen 1993; Sahling et al. 2002). We assume M. rogovi might have done the same.

Notes

Published as part of Hryniewicz, Krzysztof, Little, Crispin T. S. & Nakrem, Hans Arne, 2014, Bivalves from the latest Jurassic-earliest Cretaceous hydrocarbon seep carbonates from central Spitsbergen, Svalbard, pp. 1-66 in Zootaxa 3859 (1) on pages 16-19, DOI: 10.11646/zootaxa.3859.1.1, http://zenodo.org/record/4930112

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Linked records

Additional details

Biodiversity

Collection code
PMO
Family
Malletiidae
Genus
Mesosaccella
Kingdom
Animalia
Material sample ID
PMO 217.229 , PMO 217.371 , PMO 217.539 , PMO 224.971
Order
Nuculanida
Phylum
Mollusca
Scientific name authorship
Hryniewicz & Little & Nakrem
Species
rogovi
Taxonomic status
sp. nov.
Taxon rank
species
Type status
holotype , paratype
Taxonomic concept label
Mesosaccella rogovi Hryniewicz, Little & Nakrem, 2014

References

  • Deshayes, G. P. (1853) Traite elementaire de Conchyliologie 1, (2). Victor Masson, Paris, 273 - 368, i-xii.
  • Duff, K. L. (1978) Bivalvia from the English lower Oxford Clay (Middle Jurassic). Palaeontographical Society Monograph s, 132, 1 - 137, pls. 1 - 13.
  • Goldfuss, G. A. (1837) Petrefacta Germaniae 2 (3). Arnz, Dusseldorf, 84 pp., pls. 141 - 224, 25 pls.
  • Hodges, P. (2000) The Early Jurassic Bivalvia from the Hettangian and Lower Sinemurian of South-West Britain. Palaentographical Society Monographs, 154, 1 - 64 + vii, pls. 1 - 6.
  • Borissjak, A. (1904) Die Pelecypoden der Jura-Ablagerungen im Europaeischen Russland. I. Nuculidae. Memoires du Comite Geologique, Nouvelle Serie, 11, 1 - 49, pls. 1 - 3.
  • Forbes, E. (1845) Report on the fossil Invertebrata from Southern India, collected by Mr. Kaye and Mr. Cunliffe. Transactions of the Geological Society of London. Series 2, 7, 97 - 174, pls. 7 - 19. http: // dx. doi. org / 10.1144 / transgslb. 7.97
  • Lartet, L. (1872) Essai sur la geologie de la Palestine et des contrees avoisinantes: telles que l'Egypte et l'Arabie, comprenant les observations recueillies dans le cours de l'expedition du duc de Luynes a la Mer Morte. Suivi de Propositions de geologie et de botanique donnees par la faculte (3). Annales des Sciences geologiques, 1 - 96, pls. 9 - 12.
  • Chavan, A. (1947) La faune campanienne du Mont des Oliviers d'apres les materiaux Vignal-Masse. Journal de Conchyliologie, 87, 125 - 196.
  • Stanley, S. M. (1970) Relation of shell form to life habits of the Bivalvia (Mollusca). The Geological Society of America Memoir, 125, 1 - 296. http: // dx. doi. org / 10.1130 / mem 125 - p 1
  • Sanders, H. L. & Allen, J. A. (1985) Studies on deep-sea Protobranchia (Bivalvia); the family Malletiidae. Bulletin of the British Museum (Natural History) Zoology, 49, 195 - 238.
  • Zardus, J. D. (2002) Protobranch bivalves. Advances in Marine Biology, 42, 1 - 65. http: // dx. doi. org / 10.1016 / s 0065 - 2881 (02) 42012 - 3
  • Allen, J. A. (1993) A new deep-water hydrothermal species of Nuculana (Bivalvia: Protobranchia) from the Guaymas Basin. Malacologia, 35, 141 - 151.
  • Sahling, H., Rickert, D., Lee, R. W., Linke, P. & Suess, P. (2002) Macrofaunal community structure and sulfide flux at gas hydrate deposits from the Cascadia convergent margin, NE Pacific. Marine Ecology Progress Series, 231, 121 - 138. http: // dx. doi. org / 10.3354 / meps 231121