Surirella amphioxys

Observations

Contributor: Jonathan English - February 2011
Length Range: 28-48 µm
Width Range: 13.5-17 µm
Striae in 10 µm: 16-20

Description

Valves are 28-48 µm long by 13.5-17 µm wide with a length to width ratio between 2 and 3. The keel is low and no alar wings are visible. Valves are isopolar with cuneate apices and straight, parallel sides. The valve face is strongly undulate (structures termed "porca"). These porca appear as rectanglar structures in the LM. Each porcum is 2-3 µm wide by 4-5 µm long and is transverse by 3-4 costae, with1-2 costae between each porcum. Costae are 16-20 in 10 µm, extending from the margin to the apical axis, where they meet the axial line. Four to five rows of round areolae occur between the costae, visible only in the SEM. A distinct, flat central area occurs about the axial line. Around the valve margin are what appear to be large areolae in the LM, but in the SEM these “areolae” are actually indentations in the valve face corresponding to fibulae in the interior of the valve. Areolae on the surface of the indentations directly beneath the keel penetrate to the mantle. Indentations, or portulae occur on the mantle face, corresponding to those on the valve face.