They have a single large chloroplast, usually with four anterior lobes, which occupies most of the cytoplasmic compartment. Some species have reduced or no lobes, and some have developed posterior lobes. Like other green algal lineages, the thylakoids and lamellae have no set number or pattern within the chloroplast. The chloroplast contains one pyrenoid, which is encircled in a starch-shell, and one eyespot. The pyrenoid is usually central within the cell; the location of the stigma however, varies from species largely due to cell size and shape. The stigma is composed of two lipid-granule layers separated by a single thylakoid, which are parallel with the chloroplast membrane. Stigmas are a concentration of pigment granules which the cell uses to detect light allowing them to orientate themselves within the water column. Both the pyrenoid and the stigma can be used for taxonomic classification due to their reliable and inherent positioning in species. See figure 1 for a visual representation of the position of the chloroplast, stigma, pyrenoid, and flagellar depression.