cryptophytes

Cryptophytes, also known as cryptomonads, are a diverse group of mostly unicellular, flagellated, photosynthetic protists found in marine and freshwater environments. They are typically small to mid-sized and exhibit a variety of shapes, often with a distinct, oval or rhomboid cell body and two anterior flagella.

A defining feature of cryptophytes is their plastid, which originated through secondary endosymbiosis with red algae. The plastid is surrounded by four membranes and contains a nucleomorph, a remnant nucleus from the red algal endosymbiont housed in the periplastidial space. The plastid pigments include chlorophylls a and c and phycobiliproteins such as phycocyanin and phycoerythrin, which can give cryptophytes distinctive coloration.

Ecology and nutrition: cryptophytes are primarily photoautotrophic, but many species are mixotrophic and can ingest bacteria or other small prey. They are widespread in nutrient-rich coastal waters, estuaries, and freshwater systems, contributing to primary production and forming an important link in aquatic food webs. Their ability to hybridize phototrophy and phagotrophy allows them to exploit variable nutrient conditions.

Reproduction and genetics: reproduction is mainly asexual, occurring by binary fission, though sporadic sexual or genetic exchange events are not well documented. The nuclear genome is relatively compact, and the plastid genome, along with the presence of a nucleomorph, provides valuable insights into endosymbiotic origin and plastid evolution.

Classification and significance: cryptophytes are grouped in the phylum Cryptophyta (cryptomonads) and are studied for their unique secondary plastids and nucleomorphs. They are important model organisms in studies of endosymbiosis, photosynthesis, and aquatic ecology.