Euglenophyceae (ICNafp, proposed as a class) or Euglenea (ICZN, proposed as a class) is an unranked clade of single-celled algae belonging to the phylum Euglenozoa.
Description
Euglenophyceae are
unicellular algae,
that contain
. Their chloroplasts originated from a secondary endosymbiosis with a
green alga, particularly from the order
Pyramimonadales,
and contain
chlorophylls chlorophyll a and
chlorophyll a.
Some have secondarily lost this ability and evolved toward
osmotrophy. In addition to photosynthetic plastids, most species have a photosensitive eyespot.
Ecology
Euglenophyceae are mainly present in the
water column of freshwater habitats. They are abundant in small
eutrophic water bodies of temperate climates, where they are capable of forming blooms, including toxic blooms such as those caused by
Euglena sanguinea. In
tropical climate, blooms are common in ponds. In marine environments they have been reported in a lower amount. Some species are capable of migrating vertically through the sand along with the cycles of
. Two lineages of Euglenophyceae are part of the
marine plankton:
Rapazida and
Eutreptiales. Eutreptiales can amount up to 46% of the total phytoplankton biomass when blooming in eutrophic coastal waters.
Classification
Euglenophyceae encompasses three taxonomic groups: the
mixotrophic Rapaza viridis and two mainly phototrophic orders,
Euglenales and
Eutreptiales.
The classification is as follows (
species numbers based on
AlgaeBase):
Several genera assigned to Euglenophyceae are considered incertae sedis, because the lack of genetic data makes their phylogenetic position unresolved:
