The single-cell organism has a spherical to ovoid (egg-like) shape. The colour varies from grass green to dark green (though in deep dark water they may appear to be silver, teal, or even blackish). This is determined by the number of chloroplasts of the specimen. The surface of the cell shines like glass. The body is a thin-walled, tough, single cell with more than one nucleus. The diameter is usually from although it may get to in rare cases. The "bubble" alga is attached to the bottom by fibres: "... anchored to a substrate by minute hair-like appendages called rhizoids that create a surprisingly strong hold". 