Mastogloia crucicula (Grunow) Cleve 1895 var. crucicula

Mastogloia crucicula (Grunow) Cleve 1895 var. crucicula ( Figs 9–14 View FIGURES 9–14 )

Basionym:— Orthoneis crucicula Grunow 1877, p. 143 .

Synonym: — Mastogloia quadrinotata Østrup 1904, p. 149 , pl. 2 fig. 33.

References:— Hustedt 1933, p. 475, fig. 894; Hendey 1970, p. 145, pl. 1, fig. 8; Ricard 1973, p. 164, pl. 3, fig. 11, non fig. 12; Stephens & Gibson 1979a, p. 502, figs 17–24, 1980, fig. 42; Tomàs 1982, pl. 4, fig. 9; Navarro 1983, p. 120, figs 30, 31; Paddock & Kemp 1990, figs 32, 63, 111, 134; Hein et al. 1993, figs 16, 17, 2008, p. 63, pl. 36, figs 6, 7; John 1994, p. 193, fig. 26; Witkowski et al. 2000, p. 242, pl. 75, figs 3, 14, as M. ovulum .

Material:— Sample from Siladen, Indonesia. SEM stub no. DISVAR-ANS7SP4.

SEM morphology:— The external valve surface shows a raphe-sternum that is transapically dilated at centre into a narrow fascia that extends almost up to the valve margins ( Figs 9, 12, 14 View FIGURES 9–14 ). The raphe consists externally of two straight branches which are ending centrally and distally in expanded pores ( Figs 9, 10, 14 View FIGURES 9–14 ). Internally, the raphe branches are straight and bordered by ribs which are ending at poles in distinct and slightly raised helictoglossae ( Figs 11–13 View FIGURES 9–14 ). The transapical striae ( 18–25 in 10 µm) are uniseriate and they vary from parallel at centre to radiate at apices ( Figs 9, 12, 14 View FIGURES 9–14 ). The external openings of the areolae are rounded with a siliceous more or less crescentic edged-flap covering them (i.e., vola) and facing the valve margin, except for the first longitudinal row bordering the raphe-sternum where the areolae open to the raphe ( Figs 9, 10, 14 View FIGURES 9–14 ). There are four, sometimes three, bilobed partecta ( 0.7–1.4 µm in width) which are located in each quadrant of the valve on the valvocopula ( Figs 12 View FIGURES 9–14 , arrowhead, 13). Each partectum is ornamented with small pores arranged inwardly in parallel rows ( Fig. 11 View FIGURES 9–14 ) and communicating with the exterior through an elongate partectal pore positioned opposite to the concave side of the partectal lobe ( Figs 13 View FIGURES 9–14 , arrowhead, 14). Length: 10.2–29.1 µm; width: 6.7–11.5 µm ( Table 1).