- A relatively small, but ecologically and evolutionarily important group
- Typically phytoplankton
- In both freshwater and marine environments
- Small and delicate cells, consequently often difficult to observe and
- Distinctive structure; fairly easy to identify except for their
- Some are not photosynthetic, and are heterotrophic
- Plastids are secondary, with a highly reduced eukaryotic nucleus, the
- Many photosynthetic species probably retain ability to eat prey (mixotrophy)
- Structure & metabolism
- Flagellate unicells
- Dorsiventral, with groove and gullet on ventral side
- Some form sessile ("palmelloid") stages
- Bjornbergiella is weakly filamentous
- Two unequal flagella
- Typically the longer flagellum has two rows of mastigonemes,
the shorter one a single row
- Mastigonemes are two-parted bristles on flagella, which are
composed of a rigid, tubular base and (typically) two terminal
- Mastigonemes form within the endoplasmic reticulum (or the nuclear
envelope) and are transported to the exterior of the cell.
- Flagella are also covered with scales
- Flagellar root with rhizostile, transverse striated root, and three
- Trichocysts in oral groove, and scattered around surface of cell
- Trichocysts are composed of a tightly coiled spool of protein
- Can undergo a very rapid, irreversible conformational shift
- The trichocyst pops suddenly out of the cell, causing the cell to
jump backwards as a result
- Defense mechanism, may also be involved in predation
- Contractile vaculole at anterior end
- Large nucleus at posterior end
- Mitosis is open
- Centrioles are not associated with mitosis
- Cell division by furrowing
- Cell is stiffened by proteinaceous plates that lie inside of the plasmalemma,
and are attached to it
- Chloroplast is a secondary plastid, with a chloroplast endoplasmic reticulum
(CER) and nucleomorph
- CER is continuous with nuclear envelope, and is probably homologous
to a food vacuole.
- Origin of primary plastid remains under study
- Probably from red lineage
- Presence of phycobilins is suggestive of red algae, but is the plesiomorphic
state for plastids, and chlorophyll c is unknown among reds.
- Molecular phylogenetic studies place nucleomorph close to red algae
- Chloroplast genome map has features that suggest a reduction series
from red algae to cryptomonads to heterokonts
- Note, however, that this does not imply ancestor/descendant relationships
among the extant groups, but rather retention of ancestral character
states from common ancestors.
- Nucleomorph with three chromosomes, 240 kb, 225 kb, and 195 kb
- Does not form a spindle during mitotsis
- Plastid is a secondary plastid
- Primary plastid typically with thylakoids in pairs, with no girdle lamellae
- Chlorophylls a and c2
- Phycobilins (phycoerythrin and phycocyanin), but inside thylakoid
lumen, rather than in phycobilisomes
- Pyrenoid projects from plastid
- Carotenoids: alpha-carotene
- Xanthophylls: alloxanthin, crocoxanthin, zeaxanthin, monadoxanthin
- Eyespot, if present, is inside plastid, but not associated with
- Food storage is primarily starch, which accumulates in periplastidal
- Reproduction is generally asexual in culture.
- Sexual reproduction has recently been documented in the Cryptophyta
- Only about 12 genera are known
- Guillardia theta (formerly Cryptomonas phi) has been studied
- The complete chloroplast genome is known (Genbank accession # AF041468)
- Cryptomonas similis
- Chilomonas paramecium - nonphotosynthetic but with unpigmented
- Cyathomonas - nonphotosynthetic and lacking plastids
- Both freshwater and marine
- Important members of the nannoplankton (2-20 micrometers diameter)
- Can form major blooms in arctic and antarctic waters as well as in the
- Sometimes an important food source for smaller heterotropic or mixotrophic
plankton, including ciliates and dinoflagellates
- Myrionecta rubra (=Mesodinium rubrum) is a ciliate
that seems to acquire cryptomonad kleptochloroplasts.
- Freshwater lakes, ponds, and ditches, particularly in colder waters
- Dominant species in some antarctic lakes
- Also found in interstitial water on sandy beaches
Gibbs, S.P. 1981. The chloroplast endoplasmic reticulum: structure, function,
and evolutionary significance. Int. Rev. Cytol. 72:49-99.
Gray, M.W. 1994. One plus one equals one: the making of a cryptomonad alga.
A.S.M. News 60:423-427.
Douglas,S.E. and Penny,S.L. 1998. The plastid genome from the cryptomonad alga,
Guillardia theta: complete sequence and conserved synteny groups confirm its
common ancestry with red algae J. Mol. Evol. (1998)
Cavalier-Smith, T., et al. 1996. Cryptomonad nuclear and nucleomorph 18S rRNA
phylogeny. Eur. J. Phycol. 31:XXX-XXX.
Krugens, P. 1988. Ultrastructrure of fertilization in a cryptomonad. J.