The series of linking, siliceous bands associated with a valve. Each band is called a girdle band, or copula (from Latin for band or link; plural is copulae). Plural form is cingula.

Each valve has its own cingulum and the valves of most diatoms have a cingulum. The epivalve has the epicingulum and the hypovalve has the hypocingulum. The epicingulum always overlaps the hypocingulum. The two cingula together compose the girdle, or cincture.

Girdle bands may be secreted after the vegetative cell division that produced the valve. In other words, while the deposition of the valve is tied to cell division, the deposition of its girdle bands may not be.

Image Credit: Eduardo Morales
Scanning electron micrograph of both cingula of Staurosira construens with the bands of silica, the copulae, composing them. The arrows indicate the first girdle band, or valvocopula, of each cingulum.