Aulacoseira jewsonii Mohan & Stone, 2016

Mohan, Joseph & Stone, Jeffery R., 2016, Three novel species of Bacillariophyta (Diatoms) belonging to Aulacoseira and Lindavia from the Pliocene Hadar Formation, Afar Depression of Ethiopia, Phytotaxa 272 (4), pp. 235-247 : 240

Aulacoseira jewsonii Mohan & Stone , spec. nov. ( Figs 5 , 6 )

Valves are cylindrical, diameter ranges from 5–16 μm. Mantle height is 6–16μm. The mantle height to diameter ratio is highly variable. The diameter is typically 0.9 of the mantle height and can vary from 0.4–1.9. Frustules form filamentous chains that exhibit heterovalvy. The valve face is flat. On separation valves, acuminate spines surround the face and interlock with a sister cell’s spines. Every 3–5 spines there exists an elongated separation spine, projected into the sister cell’s separation furrow. Separation valves form costae on the mantle that conjoin to form the spines. Costae alternate with striae composed of 0.6–1.0 μm diameter areolae. Striae are straight, areolae are punctate. Typical areolae density is 8–12 per 10 μm. The collum height varies per valve and a shallow sulcus exists. Linking valve faces are flat with linking spines projected perpendicular to the valve face. Linking spines originate from a single costa and form spatulate ends that interlock with a sister cell’s linking spines. Areolae are doubly punctate to form rectangular chambers. Internal valves exhibit doubly punctate areolae and spatulate linking spines. The collum is present at the base of the valve.

Type: — ETHIOPIA. Afar Regional State: Osi Isi site, 11.31518° N, 40.73689° E, 514 m a.s.l., late Pliocene lake sediment core ( HSPDP-NAO 14-1D) material, sediment depth ~ 6 m below surface, HSPDP Northern Awash drilling team, February 2014 (holotype ANSP! GC 17185, circled specimen on slide HSPDP-NAO 14-1D-3Q-1 (93.5–95.5 cm), here illustrated as Fig. 3 :I–L).

Etymology: —Named in honor of Dr. David Jewson for his enormous contributions to the ecological and biological understanding of diatoms, especially Aulacoseira .

Remarks:— Aulacoseira jewsonii differs from A. granulata by possessing rectangular areolae on the internal valves that were likely formed by dissolution of a doubly punctate areola structure and circular areolae on separation valves ( Fig. 6 : E, F). Whereas A. granulata internal valves exhibit singly punctate rounded areola structure commonly covered with a sieve plate and rectangular areolae on separation valves ( Siver & Kling 1997), (Figs 23–28). Aulacoseira jewsonii also differs from A. granulata by possessing a separation spine every 3–5 costae (3–7 per valve) while the latter typically displays 1–3 per valve.

Order Thalassiosirales

Family Stephanodiscaceae

Genus Lindavia (Schütt) De Toni & Forti (1900: 553)

Figures

FIGURE 3. Size diminution series of A. helianthus (A–L). Holotype shown (B). Ringleiste view (A, L). Scale bars are 10 μm throughout.

FIGURE 5. Diminution size reduction series pictures of A. jewsonii taken at two focal heights to examine the diameter accurately (A–C, E–G). Three valves in a filament (D, H) the top valve is a separation valve while the bottom two are linking valves. The holotype is shown at different focal heights (I–L).

FIGURE 6. Scanning electron micrographs of A. jewsonii. Spatulate linking spines of two internal sister valves (A). Note the doubly punctate areolae that is typical of internal valves (E). Spatulate linking spines are also present on linking valves (B) that sometimes exhibit twisting costae (C).A filament of two frustules, one contains a separation valve (C) (far left), and a linking valve (middle left), the frustules on right contains two linking valves.A well preserved separation valve (D). Sister internal valves held together by spatulate linking spines (E). A single internal valve (F). A single separation valve (G).