Labyrinthina mirabilis Weynschenk, 1951

Pleş, George, Bucur, Ioan I. & Păcurariu, Adriana, 2015, Foraminiferal Assemblages And Facies Associations In The Upper Jurassic Carbonates From Ardeu Unit (Metaliferi Mountains, Romania), Acta Palaeontologica Romaniae 11 (2), pp. 43-57 : 43-44

Labyrinthina mirabilis Weynschenk, 1951

( Fig. 2 a-h)

1956 – Labyrinthina mirabilis – Weynschenk, p. 283, pl. 1, fig. 8.

1896 – Labyrinthina mirabilis – Mantea & Tomescu, pl 4, figs. 1-9.

1988 – Labyrinthina mirabilis – Septfontaine, p. 243, pl. 1, figs. 10, 12.

2005a – Labyrinthina mirabilis – Bucur & Săsăran, p. 30, pl. 2, figs. 3, 4.

2005 – Labyrinthina mirabilis – Schlagintweit et al., p. 31, fig. 13 a, b.

2008 – Labyrinthina mirabilis – Omaña & Gonzalez- Arreola, p. 803, fig. 7a.

Description: In early ontogenetic stage the test is planispirally coiled (up to 3 whorls), later becoming elongate, rectilinear up to 2.1 mm in lenght. The diameter of the coiled part ranges between 0.49 and 0.91 mm. Proloculus is globular. Chambers are separated by slightly convex septa. Vertical beams extend radially from the margins of the wall to the center, but not reaching it. Interseptal pillars are noticed in the adult uncoiled stage, mainly in the central part. They can be continuous from chamber to chamber (see Fig. 2c ). Wall agglutinated. Aperture is simple and interiomarginal in the enrolled stage, becoming multiple in the adult rectilinear stage.

Remarks: In our samples, Labyrinthina mirabilis specimens are very abundant and identified in all ontogenetic stages. An important structural feature of this species is represented by the presence of the interseptal pillars. In early ontogenetic stages pillars are less evolved or absent, accounting for the simple morphology of the chambers and aperture. In the adult uncoiled part of the test, interseptal pillars are well formed and may develop a continuous trend throughout the chambers. The labyrinthic architecture of L. mirabilis can be the result of a random fusing process between beams and pillars in the adult stage. All of the L. mirabilis specimens are found free, in contrast to some encrusting forms illustrated by Weynschenk (1956). The non-encrusting feature of the species was documented soon after by several authors ( Fourcade & Neumann, 1965; Gušić, 1968, Schlagintweit et al. 2005).

Stratigraphic range: L. mirabilis is a widespread taxon in the Upper Jurassic carbonates of the Tethyan realm. It was first described by Weynschenk (1951) from the Upper Jurassic deposits of the Sonnwend Mountains ( Austria). Other occurrences are listed in Table 1. Loeblich & Tappan (1988) included the foraminifer Lituosepta recoarensis , described by Cati (1959) from Lower Jurassic limestones, into the synonymy list of L. mirabilis . Based on this fact, the authors extended the stratigraphic range of L. mirabilis from Lower to Upper Jurassic. Septfontaine (1988) in his evolutionary classification of Jurassic lituolids, clearly explains the main differences between the two taxa and restricts L. mirabilis to Upper Jurassic (as it was described) contrasting the Upper Sinemurian Lituosepta recoarensis . Bassoullet (1997) placed the stratigraphic position of this taxon between Uppermost Oxfordian and basal Tithonian.

Figures

Fig. 2 Upper Jurassic foraminifers from the Ardeu Unit. a-h Labyrinthina mirabilis Weynschenk (a - Sample 153, b - Sample 27, c - Sample 64, d - Sample 165, e - Sample 33, f - Sample 21, g - Sample 159, h - Sample 55). i-p Parurgonina caelinensis Cuvillier, Foury & Pignatti Morano (i - Sample 65, j - Sample 36, k - Sample 129, l - Sample 30, m - Sample 23, n - Sample 65, o - Sample 38, p - Sample 64).