Staurosirella rhomboides

Valves are rhomboid and slightly heteropolar. Valves with rounded ends. The central area is broad. The valve face is slightly to clearly undulate due to raised costae. The valve face/mantle junction forms a sharp angle. The abvalvar edge of the mantle is parallel to the valve face/mantle junction. In girdle view, frustules are rectangular. Cells form short ribbon-like colonies, joined by linking spines. The axial area is lanceolate. Striae are distinct, composed of lineolae. Lineolae are greatest in length midway between the sternum and valve mantle, 6-9 in 10 µm. Lineolae bear finely branched volae. Striae are radiate and extend continuously onto the valve mantle. Costae are as broad as the striae. Spines are flat, spatulate bearing short ligulae on the side. Spines are present along the valve face edge, except at the apices, and are located on the costae between striae. Well-developed, ocellulimbus type, apical pore fields with round poroids are present. Apical pore field at headpole less developed than that of footpole. Pore fields are located at the junction between the valve face/mantle. Rimoportulae are absent. Copulae, or girdle bands, are open and do not bear perforations. Valvocopulae are wider than other girdle elements. Cells form colonies attached to the substratum by a mucilage pad.