The patterns formed by the alveolae (without or containing thecal plates), the tabulation, have been used to describe and distinguish dinoflagellate taxa for a long time. Dinoflagellates can be athecate (= without thecal plates — "empty" or amorphous material containing amphiesmal vesicles — also named naked or unarmoured), or thecate (= with cellulosic plates in the amphiesmal vesicles, also named armoured) or pelliculate (= having a dino-pellicle as principal strengthening layer of the amphiesma). Six basic types of tabulation have been recognized and are used to classify the taxa: gymnodinioid, suessioid, peridinioid, gonyaulacoid, dinophysoid, and prorocentroid. Detailed descriptions are given in, for example, Fensome et al. (1993) and Hoppenrath and Saldarriaga (2008, Tree of Life webpage for dinoflagellates, http://www.tolweb.org/Dinoflagellates/2445).