Nupela scissura

Valves are broadly elliptical-lanceolate with apiculate apices and range in size from 9 to 15 x 4.5–5.0 μm (Figs 1A–M and 2A–F). Valves of a frustule are heteromorphic with respect to raphe development and the nature of the central and axial areas. One valve possesses a fully formed raphe (Figs 1A,C–E,H,K and 2A–C) and the other lacks a raphe (Figs 1B,F,G,I,K–M and 2D–F), but has one to four elongated slits positioned in the distal part of the axial area (Fig. 3E–H). Striae are slightly radiate to parallel on the raphebearing valve, more radiate on the opposite valve and range from 48 to 58 in 10 mm. On the raphe-bearing valve, the axial area is linear to lanceolate and expands into a one-sided fascia that is rectangular to slightly bow-tie shaped (Figs 2A–C and 3A,B). On the valve bearing the raphe-like slits, the axial area is narrow near the apices, but expands into a broadly lanceolate central area with an equally broad one-sided bow-tie shaped fascia (Figs 2E,F and 3C). The fascia on this same valve is typically twice as wide as the one on the raphe-bearing valve. The raphe is linear, straight and has distal raphe fissures that deflect in the same direction down onto the mantle (Fig. 2B). The proximal raphe fissures are straight and end as small tear-drop shaped pores (Fig. 3A). Internally, the distal raphe ends terminate as small helictoglossa and the proximal raphe ends are straight and do not deflect in any direction (Fig. 2A). The valve opposite to the raphe-bearing one has one to four elongated slits aligned in a row within the distal end of the apical area (Fig. 3E–H). Externally, the areolae are elliptical to rectangular, aligned with the transapical valve axis, and covered with a hymen (Fig. 2D). Internally, the areolae are smaller in diameter, circular to elliptical and lack coverings. As a result of the different size openings, the sides of the areolae more or less taper from the wider external opening to the smaller internal openings situated in the bottom of the structure. The mantle consists of a single row of elongated areolae that also encircles the apices (Fig. 3E–H). A siliceous ridge is present along the valve margin that is often more pronounced on the rapheless valve (Fig. 2D). It should be noted that the slits on N. scissura specimens can be difficult to observe at low magnification on the external surface of valves with intact hymen coverings (e.g. Fig. 2D).

• Author
  Siver, Hamilton and E.Morales 2007
• Length Range
  9-15 µm
• Width
  4.5-5.0 µm
• Striae in 10µm
  48-58