Cryptophyceae

(botany) A class of algae of the Pyrrhophyta in some systems of classification; equivalent to the division Cryptophyta.

A small class of biflagellate unicellular algae (cryptomonads) in the chlorophyll a–c phyletic line (Chromophycota). In protozoological classification, these organisms constitute an order, Cryptomonadida, of the class Phytomastigophora. Cryptomonads are 4–80 micrometers long, ovoid or bean-shaped, and dorsiventrally flattened. The cell is bounded by a moderately flexible periplast comprising the plasmalemma and underlying rectangular or polygonal proteinaceous plates. A tubular invagination (gullet, groove, or furrow) traverses the ventral cytoplasm and opens just below the apex of the cell. A pair of subequal flagella, which are covered with hairs and small scales, arise from the center or apical end of the gullet. Cryptomonads may be photosynthetic, osmotrophic, or phagotrophic. In photosynthetic species, chloroplasts occur singly or in pairs.

Photosynthetic pigments include chlorophyll a and c, α-carotene and β-carotene (the former being predominant, an unusual ratio for algae), and red and blue phycobiliproteins closely related to those in red algae but occurring in the intrathylakoidal space rather than forming phycobilisomes. The color of the chloroplasts, and thus the color of the cryptomonad, depends upon pigment composition and may be green, olive, brown, yellow, red, or blue. Pigment composition is affected by environmental conditions.

Cryptomonads are found in fresh, brackish, marine, and hypersaline bodies of water, sometimes in great abundance. Several species are endosymbionts of marine ciliates and invertebrates, and of fresh-water dinoflagellates. See also Algae; Chromophycota; Cryptomonadida.