Thalassiosira gasseae Brindle & Mohan, 2018

Brindle, Matthew, Mohan, Joseph, Beck, Catherine & Stone, Jeffery R., 2018, Three novel species of Bacillariophyta (Diatoms) in the genera Surirella and Thalassiosira from Pleistocene Paleolake Lorenyang (~ 2 - 1.6 Ma) Turkana Basin, Kenya, Phytotaxa 371 (3), pp. 230-240 : 236

Thalassiosira gasseae Brindle & Mohan spec. nov. ( Figs. 7 & 8 )

Valves are discoid, valve face is flat, with diameter 5–10 μm. Areola are arranged in parallel to weakly curved rows across the valve face. Areolae are loculate with circular velum located on the internal wall ( Fig. 8 , C). Externally the areolae exhibit flat foramen. Fultoportulae are sparsely distributed around the valve margin. Externally the fultoportulae are simple, internally they are raised, circular, and exhibit four satellite pores. A single rimoportula is present between two fultoportulae ( Fig. 8 , B & D). Externally the rimoportula is simple and much larger than fultoportula ( Fig. 8 , A). Internally the rimoportula is simple and raised more near the center of the process ( Fig. 8 , D).

Type: — West Turkana Kaitio , northwestern Kenya, (4.109722° N, 35.871781° E) Pleistocene lake sediment core of the Natoo Member of the Nachukui Formation sediment core ( HSPDP-WTK13-1 A) material, sediment depth ~ 60 meters below surface, collected by Feibel, C., Cohen, A., & Beck, C., July 2013, holotype, designated here ; deposited in ANSP! (Circled specimen on slide WTK 203, illustrated herein as Fig. 7 , A).

Etymology: — Thalassiosira gasseae is named in honor of the original discoverer of this species. Françoise Gasse has contributed greatly to the understanding of modern and fossil diatoms with exceptional regards to the East African Rift Valley.

Remarks:— Gasse (1986) (Pl. 4, Figs. 11–15) reported this species from the Geradila Salt Marsh in the Gadeb Plains of Ethiopia but did not designate a species name. Thalassiosira gasseae has a similar size range to T. minima Gaarder (1951: 31) however, T. minima exhibits central fultoportulae while T. gasseae lacks central fultoportulae.

Figures

FIGURE 7. LM Thalassiosira gassaea. Size diminution series of Thalassiosira gassaea. Images taken at x1000. Scale bar is 2 μm. A is the holotype.

FIGURE 8. SEM Thalassiosira gassaea. Scanning electron micrographs of Thalassiosira gassaea. The exterior of the valve (A) is marked by sparse marginal fultoportulae and a single large rimoportula (arrowed). The interior of the valve exhibits a simple rimoportula with raised lips near the middle of the aperture and reduced near the outside ends of the aperture (D). The fultoportulae are slightly raised with four satellite pores, the areolae are marked with elliptical velum that are slightly depressed into interior valve surface. Internal views of the valve (B & C) show overall valve structure, rimoportula is closely associated with one fultoportula (B & D).