Entogoniopsis squamatoportulata P.A. Sims, J. Witkowski, N.I. Strelnikova & D.M. Williams, 2015

Witkowski, Jakub, Sims, Patricia A., Strelnikova, Nina I. & Williams, David M., 2015, Entogoniopsis gen. nov. and Trilamina gen. nov. (Bacillariophyta): a survey of multipolar pseudocellate diatoms with internal costae, including comments on the genus Sheshukovia Gleser, Phytotaxa 209 (1), pp. 448-450 : 448-450

9. Entogoniopsis squamatoportulata P.A. Sims, J. Witkowski, N.I. Strelnikova & D.M. Williams , sp. nov.

(SEM: Figs 120–124 ; LM: Figs 125–127 )

TYPE (here designated):— South Tasman Rise, Southwest Pacific Ocean , DSDP sample 29-281-16-3, 75-77 cm (SZCZ21078, holotype! = Fig. 127 ) .

Valves triangular, with acute to slightly rounded poles, and straight sides ( Figs 120 , 125–127 ). Entire valve face is depressed ( Fig. 122 ), apart from raised poles with prominent pseudocelli ( Figs 120, 122 ). A hyaline marginal ridge extends between each pseudocellus. Whole valve face is perforated by radially oriented poroid areolae occluded by volae ( Figs 120, 123 , 125–127 ). Marginal zone with small areolae, more closely spaced than those within the central depression ( Figs 125–127 ), which are also variable in size and shape. A well-defined ring of rimoportulae is located in the valve face centre or around the central area ( Fig. 120 ), with internal openings in the form of slits across slightly raised papillae ( Fig. 121 ). Mantle steeply downturned, shallow, perforated by volate poroid areolae arranged in rows parallel to the pervalvar axis ( Fig. 124 ). Margin of the mantle smooth, hyaline, slightly expanded inwardly ( Fig. 124 ). The expanded mantle margin on valve interior gives rise to a complex network of internal costae that intersect at multiple angles, forming a series of prominent ‘loops’ along each margin of the valve face ( Figs 120, 124 ). The costae reach a short distance toward the centre of the valve face ( Fig. 120 ), and are manifested on the valve face exterior by defining sectors, in which occur the marginal areolae ( Figs 125–127 ). Measurements (n= 8): average side length: 211.6–359.8 µm; 1 costa in 10 µm measured along the valve face margin; 2 areolae in 10 µm in marginal sectors; 1.5–2 areolae within the central depression; 9–18 rimoportulae; 4–5 porelli in 10 µm.

Etymology:—Named for its superficial resemblance to E. squamata and the presence of the prominent central ring of rimoportulae.

Geographic and stratigraphic distribution ( Fig. 10, sites 12, 19):

Middle Eocene : Falkland Plateau, South Atlantic: Vema Cruise 17, Core 107: BM stub P.1274 ( Figs 120–124 ).

1. Pantocsek referred to the scaly pattern produced by the internal costae, hence the Latin epithet ‘squamatum’

20 • Phytotaxa 209 (1) © 2015 Magnolia Press

WITKOWSKI ET AL.

Late Eocene: South Tasman Rise, Southwestern Pacific Ocean: DSDP Site 281, Cores 281-14 through 281-16: SZCZ15073,

21078 ( Figs 125–127 ), 22054–22057.

Observations:—Despite numerous hours of careful search, only a single specimen revealing the structure of the valve interior was available for SEM examination. Therefore, external openings of the rimoportulae were not observed in SEM, but LM observations strongly suggest that the external openings are in the form of simple slits.

Figures

FIGURES 120–124. Scanning electron micrographs of Entogoniopsis squamatoportulata from Vema Cruise 17, Core 107, South Atlantic Ocean. Fig. 120: Internal valve view, showing the location of the central ring of 17 rimoportulae (arrow). Fig. 121: Detail of the specimen in Fig. 120, showing the internal openings of the rimoportulae in the form of short slits across slightly raised papillae. Fig. 122: Oblique internal view, showing the depressed centre of the valve face, and the complex pattern of internal costae in the marginal part of the valve face and on the mantle. Fig. 123: Detail of the prominent pseudocellus. Note the well-preserved volae within the areolae. Fig. 124: Detail of the pattern formed by the internal costae. Note the inwardly expanded, smooth hyaline margin of the mantle (arrow).

FIGURES 125–127. Light micrographs showing the range of morphological variation in Entogoniopsis squamatoportulata. Figs 125–126: SZCZ22057, DSDP sample 29-281-16CC, South Tasman Rise, Southwest Pacific Ocean. Fig. 127: SZCZ21078, holotype, DSDP sample 29-281-16-3, 75–77 cm, South Tasman Rise, Southwest Pacific Ocean.