Mastogloia peracuta Janisch, 1893

Lobban, Christopher S., 2015, Benthic marine diatom flora of Guam: new records, redescription of Psammodictyon pustulatum n. comb., n. stat., and three new species (Colliculoamphora gabgabensis, Lauderia excentrica, and Rhoiconeis pagoensis), Micronesica 2015 (2), pp. 1-49 : 8

Mastogloia peracuta Janisch Figs 64–67

Section Decussatae

Ref. illus.: Hustedt 1931 –1959, fig. 906; Ricard 1974, pl. 4(22), fig. 12; Montgomery 1978, pl. 132, figs E, F (as Mastogloia rhomlus [sic] (Petit) Cleve); Navarro 1983a, figs 52, 53; Yohn & Gibson 1992, figs 1–6; Hein et al. 2008, pl. 43, fig. 1; Loir & Novarino 2013, pl. 18a

Samples: GU44AP-9

Dimensions: Length 27–29 µm, width 14–16 µm; striae 17 in 10 µm.

Diagnostics: Rostrate valves with coarse, transapically elongate areolae in decussate pattern, with a band of smaller, square areolae along the margin. Raphe straight, central endings close together.

Comments: Our specimens do not entirely agree with Hustedt’s (1931 –1959) description, especially that the transapical length of their areolae does not gradually increase from the raphe to the margin and that the apical partecta, while wider than the others, are not twice the width. Nevertheless, it does match more recent descriptions and SEM observations ( Yohn & Gibson 1982, Loir & Novarino 2013), with the exception of the external appearance of the areolae depicted by Paddock & Kemp (1990, fig. 44). Hustedt (1931 –1959) contrasted it with the very similar M. rhombus (Petit) Cleve & Grove. In our flora it resembles M. lacrimata Voigt ( Lobban et al. 2012, pl. 30, figs 6–8) in the large, decussate pattern of transapically elongate areolae, though in the latter the transapical striae are noticeably curved, and the partectal chambers readily distinguish it.

Figures

Figures 51–70. Figs. 51–55. Mastogloia emarginata. Figs 51-54. LM views of two specimens focused on valve face and valvocopula, arrowhead indicates one of the prominent exit pores of the partecta (GU44AR-2) (DIC). Fig. 55. Internal view of valve and valvocopula (GU55B-4) (SEM). Figs 56, 57. Mastogloia ovulum specimen at two focal planes (GU44K-6) (DIC). Figs 58-61. Mastogloia matthaei, two specimens at two focal planes (GU52P-2) (DIC). Figs. 62, 63. Mastogloia obliqua, valve at two focal planes (GU66F-4) (DIC). Figs. 64–67. Mastogloia peracuta (GU44AP-9). Figs 64, 65. Specimen at two focal planes (DIC). Figs 65, 66, External views of two specimens in SEM. Figs 68–71. Mastogloia pumila. Figs 68, 69. Specimen in DIC at two focal planes (GU52P-1; catalog # GUD002950). Fig. 70. Internal aspect of valve and valvocopula (GU52P-9) (SEM). Fig. 71. Frustule showing both internal and external valve faces. Scale bars: Figs 51–69 = 5 µm, Figs 70, 71 = 3 µm.