Entogonia briggeri Dumitrică, 2017

Dumitrică, Paulian & Martin, Simona Saint, 2017, Entogonia Briggeri N. Sp., A New Diatom Species From The Middle Miocene Of Romania And New Insights On The Fossil Marine Diatom Genus Entogonia Greville, Acta Palaeontologica Romaniae 13 (2), pp. 21-35 : 24-27

Entogonia briggeri Dumitrică and Saint Martin nov. sp.

Figs. 3-7

Description. The valves are tripolar with straight to slightly convex sides in valve view and round poles ( Figs. 3 a-f, 4a, 4c, 4f, 5a-b, 7a). Each pole bears an elevation circular to oval in outline and slightly raised above the surface of valve, with a height of about 17.5 µm. They are perforated by irregularly scattered areolae that are smaller than the valve areolae ( Figs. 3 a-f, 4b, 4c, 4e). Apices of the elevations are flat, finely punctate (perforate) with no particular arrangement of puncta as it can be seen in external valve view ( Figs. 3e , 4d ) and also in internal valve view ( Fig. 5f ). The diameter of apices is of circa 17 µm. On each apex there is a flat, triangular, claw-like linking spine on one lateral border ( Figs. 4b , 6b ). The length of spines is variable between 24-25 µm. Exit pores arise gently from the valve face close to elevations; they are circular to oval in outline, with a diameter smaller than that of the elevations, of about 8.7- 10.5 µm. ( Figs. 3a, 3c, 3e , 4a, 4c , 7a ). They have a protruding hyaline lip which does not surround the entire circumference of the exit pores as they are missing towards the projections ( Fig. 4d ). The valve face is perforated by poroid areolae exhibiting different dimensions and distribution patterns that delimit an outer triangle and an inner triangle ( Figs. 3 a-e, 4a, 4c, 4f, 7a). In external oblique view the outer triangle is gently elevated relative to inner triangle ( Fig. 4e ). The outer triangle is broad, convex in girdle view, with areolae arranged in 2-3 transverse rows between two internal costae as follows: the rows adjacent to internal costae comprise larger and closely spaced areolae (4-5 within a row); the rows locat- ed away from internal costae comprise smaller and more distantly spaced areolae (2-4 within a row); sometimes the rows of these smaller areolae are incomplete. The row of larger areolae which lie next to and parallel to each internal costae of the outer triangle are also much larger than those of the inner triangle ( Figs. 3a, 3b, 3e , 4a, 4c - d ). Rows are generally perpendicular to the valve face margins. Internal costae vary in number from 10 to 12 depending, but not compulsorily, on the size of the valve and continue down the mantle until they fuse with the margin of the mantle ( Figs. 4f , 5 a-b, 7b). The internal costae of the outer triangle define sectors for areolae both on the valve face and on the mantle. The inner triangle presents straight or concave sides of circa 90-110 µm outlined on the valve surface by a deep constriction corresponding on the inner face to a costa ( Figs. 4f , 5 a-b). The central part of this triangle is depressed as seen in external oblique view ( Fig. 4e ) and sometimes hyaline ( Fig. 3c ). In internal view, from this center radiate a large number of dense costae which reach the boundary between the inner and outer triangles and which can be simple or bifurcate ( Figs. 5 a-b, 7b). Three such costae extend along the bisectors of the three corners and continuously ramify on both sides forming a dense network of costae. These three bisecting costae are never straight as in other species or more prominent than the resulted branches ( Figs. 5 c-e). The fine areolae of the inner triangle are dense, small and arranged in radial, circular or spiral rows, neither of them perfect ( Figs. 4a, 4c , 7a ). Inner coils very delicate, with annular costae joined to one another by curved and more delicate bars ( Figs. 5 a-f). There is no clear distinction between valve face and valve mantle since valve areolae pattern is continuous on the mantle. Mantle vertical of about 29-35 µm height. There is also a basal ring of enlarged pores with protruding lips, which occur between internal costae on the valve mantle ( Figs. 4b, 4e , 6a , and especially 6c). A thin hyaline ridge is placed on the mantle edge, bordering this latter with the valvocopula ( Figs. 4b, 4e ). In internal view, it can be observed inwardly expanded hyaline mantle margin ( Figs. 4f , 5 a-b).

Cingulum composed of a closed valvocopula and one or two closed copulae. All are ornamented by areolae, but areolae of valvocopula are slightly smaller than those of copulae and of mantle. Valvocopula, with a pars exterior varying between 12.6-20 µm high, bears areolae arranged in almost vertical rows ( Figs. 6 a-b). There is a more conspicuous row of coarser and regularly arranged areolae of 2 µm diameter adjacent to the valve mantle ( Figs. 6 a-b). The copulae, with a pars exterior varying between 24-30 µm heigh, bear areolae arranged in diagonal rows ( Figs. 6 a-b). Sometimes, at the corners of copulae the pattern of the areolae seems slightly disturbed ( Figs. 6 a-b). All girdle elements observed (valvocopula and copulae) have a hyaline abvalvar margin 3-4 µm deep.

In girdle and oblique views the mantle margin appears slightly undulate ( Figs. 4e , 6a ).

Holotype: Figs. 3a,b , MNHN.F. F62406 ( Muséum National d’Histoire Naturelle , Paris, France)

Isotype 1: Figs. 3c,d , MNHN.F. F62407 ( Muséum National d’Histoire Naturelle , Paris, France)

Isotype 2: Fig. 3e , MNHN.F. F62408 ( Muséum National d’Histoire Naturelle , Paris, France)

Isotype 3: Fig 3f , MNHN.F. F62409 ( Muséum National d’Histoire Naturelle , Paris, France)

Dimensions. Length of sides of the outer triangle 150-200 µm.

Remarks. Study of Entogonia specimens recorded in the three stratigraphic levels mentioned above has proven that all of them belong to a single species, Entogonia briggeri n. sp., that has many characters in common with both Entogonia hungarica Holmes & Brigger, 1979 ( Holmes & Brigger, 1979, p. 182, figs. 66-72) and Entogonia formosa (Truan & Witt) Bergon 1892 ( Holmes & Brigger, 1977, fig. 55-57; 1979, p. 179, figs 54-57, 58- 59).

Entogonia briggeri n. sp. resembles very much E. hungarica Holmes & Brigger, 1979 in the morphology of the outer triangle, shape of the inner triangle and sometimes the ratio between the diameter of the exit pores and of the elevations. However, the diameter of the exit pores is generally smaller in this species than in E. hungarica . The most evident difference from the latter species regards the costae of the inner triangle, which are here and there absent or interrupted in E. hungarica , leaving areas without costae. Also, in E. hungarica there is no hyaline central area onto the inner triangle, at the origin of the internal costae, as we observed in E. briggeri n. sp. Another evident difference concerns a row of enlarged pores which occur between the internal costae on the valve mantle. This character is present in E. briggeri and absent in E. hungarica .

Entogonia briggeri n. sp. is wholly comparable with the early Middle Eocene specimens from Conset, Barbados, assigned to E. formosa (Truan & Witt) Bergon by Holmes & Brigger (1977, fig. 55-57), from which it differs especially in the greater number of costae in the inner triangle, denser areolae in the outer triangle, and in the presence of enlarged pores which occur between to the internal costae on the valve mantle. These pores, as observed by Holmes & Brigger (1979), are characteristic in some species as for instance: Entogonia amabilis Greville, 1863 , E. marginata (Bright.) Greville, 1863 , E. pulcherrima (Greville) Greville, 1863 , E. reinholdii Holmes & Brigger, 1979 , E. robinsonii Holmes & Brigger, 1979 .

Range and occurrence. Upper Middle Miocene, (lower part of Upper Badenian = Kossovian substage): Radiolarian Shale Formation from Getic Depression: Tilvici Valley, Păuşeşti Otăsău village, and Valea Sărată (Salted Valley), Ocnele Mari village, both in Râmnicu Vâlcea district, Romania; also lower Sarmatian (late Vohynian) from Borod Basin, Romania.

Type locality. Tilvici valley, Păuşeşti Otăsău village, Râmnicu Vâlcea district, Romania

Etymology. The species is dedicated to A. L. Brigger to honor his contribution to the knowledge of the genus Entogonia .

Figures

Figs. 3a-f Entogonia briggeri n. sp., sample 1315. LM views; a Holotype, valve view; b Same specimen figured in 3a focused on internal coil; c Isotype 1, valve view; d Same specimen figured in 3c focused on internal coil; e Isotype 2, valve view; f Isotype 3, valve view. Scale bars: 20 µm.

Figs. 4a-f Entogonia briggeri n. sp., sample 1315; SEM external views (a-e) and SEM internal view (f). a Valve face exhibiting specific morphological features; b Girdle view showing elevations and one triangular spine on each elevation; c Valve face showing valve shape, round apices, elevations to poles (arrow) and exit pores (head arrow), areolae pattern on inner and outer triangles; d Detail showing the finely punctuated apices of elevation and exit pore close to elevation with a protruding hyaline lip; e Oblique valve view showing raised outer triangle, depressed central part of inner triangle, vertical mantle with one ring of enlarged pores (arrows); f Internal view showing the outer and inner triangles, internal costae, internal coil system. Scale bars: 20 µm.

Figs. 5 a-f Entogonia briggeri n. sp. sample 1315; SEM internal views; a-b Internal view illustrating the outer and inner triangles, internal costae, and internal coil system; c-d Details of poles of the specimen figured in b showing the ramifying of some costae to form a dense network, hyaline center of the inner triangle, inner coil with costae joined to one another by curved bars; e Detail of a pole showing the apices of the coil fusing to a siliceous punctate membrane within the exit pore on the side of the orifice touching the elevation; f Detail of a pole of the specimen figured in a showing the internal view of the elevation with delicate puncta. Scale bars: 20 µm.

Figs. 6a-d Cingulum of Entogonia briggeri n. sp., sample 1315; a Girdle view showing a valve with part of a cingulum composed of the valvocopula (vc) and two copulae (c). Note on valvocopula the vertical pattern of areolae and single row of coarser areolae regularly arranged adjacent to the valve mantle (head arrow). Areolae arranged in diagonal rows on copulae; b Girdle view of an incomplete frustule showing the hypovalve (h) with its valvocopula (vc) and one partly visible copulae (c) and a part of the epicingulum consiting of two copulae (c). Note on the valvocopula and also on the copulae a hyaline abvalvar margin (arrows); c Detail of specimen figured in a exhibiting the ring of enlarged pores occurring between internal costae on the valve mantle; d Detail of specimen figured in Fig. 4a showing the areolae size and pattern into the outer and inner triangle. Scale bars: 20 µm.

Figs. 7 a, b Entogonia briggeri n. sp., sample 102m; SEM external view (a) and SEM internal view (b); a Valve face showing valve shape, round apices, elevations to poles and orifices, areolae pattern on inner and outer triangles; b Internal view showing the outer and inner triangles, internal costae of outer triangle, dense network of costae of the inner triangle, hyaline center of the inner triangle, the apices of the internal coil fusing to a siliceous punctate membrane within the orifice. Scale bars: 20 µm.