Mastogloia lucayensis

Description – LM morphology:

Valves elliptical (smaller cells) to narrowly elliptical (larger cells) with rostrate (smaller cells) to rostrate-capitate (larger cells) apices (Figures 2C, 10). Valve measurements: length 27–45 μm, width 9–13 μm, length to width ratio 2.5–4.2, n = 25. Axial area narrow (Figures 2C, 10A, C, E, F). External raphe branches slightly sinuous (Figures 2C, 10A, C, E, F). External central raphe ends straight, simple, terminating slightly within nearly circular central area (Figures 2C, 10A, C, E, F). Valve pattern forming 3 zones within each hemivalve: a paraxial zone with a longitudinal row of punctate pores that are interrupted around the central area, a marginal zone of radiate striae, 12–16 in 10 μm, n = 25, and a lateral unornamented area that occupies most of the valve face (Figures 2C, 10A, C, E, F). Partecta extending to near apices (partecta density = 5–8 in 10 μm, n = 22), nearly square to slightly transapically elongated rectangular (width = 1.0–1.8 μm, n = 21) with very slightly convex inner margins; terminal partecta distinct from rest, slightly longer with rounded inner margins (Figures 10B, D, G).

Description – SEM morphology:

External valve face nearly flat and mostly unperforated except for single rows of paraxial pores on each side of the raphe and double longitudinal rows of oppositely arranged pores along the valve face/mantle junction (Figures 11A, B, D, E). Alveolate striae in fully developed and intact valves are barely, or not at all, evident using SEM, except for their pore openings. Each alveolar stria has one paraxial pore and two pores at the valve face/mantle junction (Figures11 B, D, E). External alveolar pores small, punctate (Figures 11A, B, D, E). The external pores at the valve face/mantle junction slightly larger than the paraxial pores (Figures 11A, B, D, E). Valve face/mantle transition gradual but demarcated by the double longitudinal row of pores (Figures 11A–E). Raphe slightly sinuous within narrow axial area bounded by rows of paraxial pores (Figures 11A, B, D, E). External central raphe ends simple, straight, terminating near each other (Figure 11A). External apical raphe ends simple, hooked towards one side of the valve, terminating at valve margin (Figures 11A–C).

Internal valve face traversed by transapical costae bordering each alveolus (Figures 12A, B, E, F) and two longitudinal costae in the mantle area extending to and converging towards the apices (Figures 12A, B). Areas between transapical costae infilled and thickened in the middle portions of each hemivalve obscuring the transapical costae (Figures 12A, B, D–F). Internal pores of the alveolate striae located within unthickened depressions of the internal valve surface located adjacent to the elevated internal raphe ridge and along the valve face/mantle junction (Figure 12B arrows, D). Internally on each side of the elevated raphe ridge is a longitudinal row of circular pores of the alveoli (Figures 12B, D). The longitudinal rows are interrupted around central nodule (Figures 12A, C, E, F). The alveolar pores of the longitudinal rows are located at the two corners of the paraxial depressions adjacent to the raphe ridge (Figures 12B, D). Within each alveolus, the two corner-located internal alveolar pores along the internal raphe ridge do not align with the single external pore per alveolus along the raphe. In the internal mantle area, alveolar pores (8 per alveolus) straddle the intersections of the transapical and longitudinal costae forming two longitudinal, double pore rows in the internal mantle area (Figures 12A, B). Small pseudoseptum at each apex, indented at a sharp angle at the internal margin (Figures 12A–D). Internal raphe branches straight, within elevated raphe ridge (Figures 12A–F). Internal central raphe ends straight, simple, terminating at edge of circular central nodule (Figures 12A, C, E, F). Internal apical raphe ends straight, simple, surrounded by helictoglossae (Figure 12D).

Cingulum composed of closed, partectate valvocopulae and one additional open copula on the epicingulum (Figures 11B, C). The valvocopulae have a lacuna at each apex (Figures 12C, D). Each partectum perforated by six transapical, linear, double rows of very small circular poroids (Figure 12D). The double rows do not extend to the full width of the partecta but terminate irregularly before reaching the internal partectum margin (Figure 12D). Externally, partecta exit pores transapically elongated, dash-like (Figure 11E) to rectangular (Figures 12E, F).

• Author
  Lobban and Frankovich 2023
• Length Range
  27-45 µm
• Width
  9-13 µm
• Striae in 10µm
  12-16