All Taxa

Amphipleuraceae: Amphipleura

Cells with lanceolate, linear-lanceolate or linear valves, valve margins tapering to rounded or acute ends.

Isopolar, isovalvar, bilaterally symmetrical.

Striae uniseriate, parallel, with small, very regularly spaced areolae; areolae opening externally via a narrow, apically elongated slit, internally circular and occluded by a fine pore plate (hymen).

Raphe slits short or very short, positioned towards the valve ends, separated by a long, narrow axial area; external raphe endings all simple or slightly expanded. Internally raphe sternum (i.e. the part of the axial area containing a raphe slit) bears a thick longitudinal rib on each side of the raphe, which combines with the helictoglossa to form a characteristic beaked structure (the ‘porte-crayon’ structure described by Cleve) at each pole; the rest of the axial area bears a single narrow rib; central area absent.

One central H-shaped plastid (as seen in valve view), consisting a central bridge appressed to one valve and containing a pyrenoid, from which two large lateral plates extend beneath the girdle to the opposite valve.

Cells solitary and unattached, or occurring loosely associated in mucilaginous masses.