Pleurosigma javanicum Grunow
Valves are lanceolate and sigmoid with somewhat acute apices (Fig. 1, exterior of entire valve, SEM). The raphe system is median through most of its length, approaching the margin near the apices (Fig. 3, detail of Fig. 1), where the distal raphe ends curve around the ends of the valve. Several isolated areolae are present at the extreme tip of the valve. The central area is rather small, and the raphe ends overlap and curve sharply away from each other on the valve exterior (Fig. 2, detail of Fig. 1). The external foramina of the areolae are slit-like. The apical axis (length) is 107-136µm and the transapical axis (width) is 25-28µm. The transverse striae are 24-25 in 10µm and the oblique striae are 20-21 in 10 µm, crossing at an angle of 64 degrees.
A brief description was presented initially in Cleve & Grunow (1880), later expanded by Cleve (1894). The IRL material corresponds to the original type material from Java, in Cleve & Möller Type Slide 145 (Sterrenburg, personal communication, 18 November 2013). That suggests a tropical preference for this species. Although quite rare in the IRL, it was found in the Banana River and south to the Jupiter Inlet at various times of the year, and may have been misidentified as P. rigidum or as P. angulatum. Both of these have been previously described from the IRL.