Mastogloia variabilis, Graeff, Kociolek & S.R. Rushforth, 2013

GRAEFF, C. L., KOCIOLEK, J. P. & RUSHFORTH, S. R., 2013, New and Interesting Diatoms (Bacillariophyta) from Blue Lake Warm Springs, Tooele County, Utah, Phytotaxa 153 (1), pp. 1-38 : 22-25

Mastogloia variabilis, Graeff, Kociolek & S.R. Rushforth , sp. nov. ( Figs 106–124 ; figure 108 =

holotype)

Valves broadly linear, tapering to protracted, blunt apices ( Figs 106–115 ). Some specimens are asymmetrical to the transapical axis ( Figs 110–111, 113 ). Length 43–68 µm, breadth 15.5–18.0 µm. The axial area is straight, forming an elliptical to nearly rectangular central area not extending to the margin ( Figs 106, 108, 112 ). The central area can be asymmetrical, with one side of the axial area larger than the other, and having the appearance of “ghost” striae beneath it ( Figs 107, 115 ). The raphe is lateral, undulate ( Figs 106, 108, 111–113 ), with dilated, rounded external proximal ends ( Figs 106–108, 111–115 ) and distal ends deflected in the same direction ( Figs 108, 112–114 ). Striae are distinctly punctate, radiate across most of the length of the valve except at the ends where they are parallel ( Figs 106, 108, 111 ) or slightly convergent ( Figs 107, 112 ). Striae number 15–17/ 10 µm and internal areolae within a stria number 30–34/ 10 µm. Ridges of silica are visible on either side of raphe ( Figs 109–110 ). The partecta appear arched, not straight, following the contour of the valve margins. Partecta chambers are small, rectangular to nearly square in shape, 5–7/ 10 µm. The chambers extend about ⅔ the length of the valve, present in the middle portion only.

In the SEM, the valve exterior has radiate striae that become nearly parallel at the apices ( Figs 116–117 ), with round to elliptical areolae ( Figs 118–119 ). The raphe is distinctly undulate ( Fig. 116 ), terminating proximally with enlarged ends and terminating distally with curved ends deflected onto the mantle ( Figs 116, 118 ). The terminal area is expanded, with few areolae present ( Figs 116–118 ). The central area is thickened, and has depressions in it giving the margin a mottled appearance ( Figs 116–117, 119 ), which appear as the ghost striae in the LM. The outer openings of the partecta are enlarged and elliptical to rounded ( Fig. 122 , white arrows). Internally, the valve is dominated by a band or ridge of silica bordering the raphe on either side ( Figs 120–121, 123–124 ). This band is connected to the axial area, and appears flexible, not rigid. There is a narrow, elongate central nodule ( Figs 121, 123 ), and the helictoglossae are well-developed ( Figs 120, 124 ). There is a pseudoseptum at each valve apex ( Figs 121, 124 ). The valvocopulum has a small septum at each end ( Figs 120, 124 ), and the partecta are small and rectangular ( Figs 110 , 120, 123 ). There are distinct round perforations in the valvocopulum near the mantle of the valve that appear to correspond to larger openings on the exterior of the valvocopulum ( Fig. 120, 122–123 ). The partectal chambers are without poroids ( Figs 122–124 ). Internally the areolar openings are in the form of quincunx ( Figs 122–124 ).

Type: — USA. Marsh south of Blue Lake , Tooele Co., Utah. ( COLO 439079 , holotype! (= Fig. 108 ), designated here; COLO 8528 , BM 101681, isotypes)

Etymology:—This species is named for its variable valve outline.

Distribution: — Mastogloia variabilis was most common in a collection scraped from a stick in the main basin of Blue Lake (COLO 8510) and can also be found more rarely in the surrounding marshes.

Observations: — Mastogloia variabilis belongs to the Apiculatae group of the genus, as presented by Hustedt (1959) and later considered by Stephens & Gibson (1980), who show M. apiculata W. Smith (1856: 65), which they illustrate as having the areolar structure similar to that of M. variabilis . Paddock & Kemp (1990: fig. 94) show the areolar structure of another member of the Apiculatae, M. robusta Hustedt (1933: 518) , similar to that of M. variabilis . Paradoxae ( Hustedt 1959) is another group of Mastologia that has longitudinal ribs, and taxa belonging to this group can be distinguished in the LM from those of Apiculatae by their partecta, which are spaced noticeably away from the valve margins ( Stephens & Gibson 1980: figs 21– 22, 25, Hustedt 1959: figs 953–958). Images of M. paradoxa Grunow in Cleve & Möller (1878: no. 153), a member of the Paradoxae, suggest that the areolar structure of Paradoxae is quite different from that of Apiculatae ( Paddock & Kemp 1990: figs 92, 95) and that poroids can be present on the partectal chambers in the group ( Stephens & Gibson 1980: fig. 26). Apical septa and pseudosepta are common in but not unique to Apiculatae ( Paddock & Kemp 1990, Hustedt 1959).

M. variabilis can be distinguished from other members of Apiculatae by its relatively large central area and its sometimes asymmetrical valves. Like M. baltica Grunow in Van Heurck (1880: pl. 4, fig. 24) (see also Witkowski et al. 2000: 239, pl. 74, figs 13–16), another member of the Apiculatae group ( Hustedt 1959: 517, fig. 949), M. variabilis can have protracted apices. However, a large central area like that seen in M. variabilis appears to be rather rare among Mastogloia species ; Voigt (1942: 10, fig. 28) pictures M. elegantula Hustedt (1933: 541) , which is a species with a large central area and capitate apices but no longitudinal ribs.

Previous collections of members of Apiculatae by various authors suggest that the group generally prefers saline habitats and tends to be found in coastal or island areas. Specimens from Apiculatae pictured by Paddock & Kemp (1990), of the taxa M. robusta and M. labuensis var. lanceolata Hustedt (1933: 518) , are from Ely’s Flats, Bermuda and the coastal town of Dilesi, Greece, respectively. M. citrus (Cleve) De Toni (1891: 320) has a tropical marine distribution ( Martinez-Goss & Evangelista 2011). Stephens & Gibson (1980) indicate M. apiculata occurs in saline environments in the USA and England. Hustedt (1959) and Cleve-Euler (1953) list the known localities of other members of Apiculatae as being coastal or island areas. Witkowski et al. (2000) indicate that the Indian Ocean, Mediterranean Sea, and New Caledonia are also locations from which Apiculatae species can be collected.

Figures

FIGURES 106–115. LM. Mastogloia variabilis. Valve views showing size diminution series. Figure 108 is the holotype. Note the variable degree of transapical valve symmetry. Figures 109 and 110 show the partecta structure at different focal planes. Scale bar: 10 µm.

FIGURES 116–119. SEM. Mastogloia variabilis. External views of three specimens. Fig. 116, Full valve view showing undulate raphe branches and especially protracted apices. Fig. 117, Specimen with large central area and many depressions on the central area. Fig. 118, Large, deflected distal raphe end, free of striae. Fig. 119, Central area showing dilated proximal raphe ends. Scale bars: Figs 116–117: 10 µm; Figs 118–119: 1 µm.

FIGURES 120–124. SEM. Mastogloia variabilis. Internal views of four specimens. Fig. 120, Full valve view of a large specimen with a large central nodule and helictoglossa. Fig. 121, View showing the pseudoseptae and internal structure of the central area. Fig. 122, View of the valvocopulum showing the internal and external openings and the surface lacking poroids, indicated by white arrows. Fig. 123, Internal openings in the valvocopulum, straight proximal raphe ends, and inconsistent quincunx form of the areolae near the valve center. Fig. 124, Apex showing the valvocopulum with a small septum sitting on top of the valve pseudoseptum. The quincunx form of the areolae is apparent. Scale bars: Figs 120–121: 10 µm; Figs 122–124: 1 µm.