The
haptophytes, classed either as the Prymnesiophyta or Haptophyta, are a
phylumIn biology, a phylum ["Phylum" is adopted from the Greek phylai, the clan-based voting groups in Greek city-states.] is a taxonomic rank below Kingdom and above Class...
of algae.
The term "Haptophyceae" is sometimes used. This ending implies classification at a lower level. However, although the
phylogeneticsIn biology, phylogenetics is the study of evolutionary relatedness among various groups of organisms , which is discovered through molecular sequencing data and morphological data matrices...
of this group has become much more well understood in recent years, there remains some dispute over which taxon level is most appropriate.
Characteristics
The
chloroplastChloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.The word chloroplast is...
s are pigmented similarly to those of the
heterokontThe heterokonts or stramenopiles are a major line of eukaryotes presently containing more than 100,000 known species, most of them diatoms. Most are algae, ranging from the giant multicellular kelp to the unicellular diatoms, which are a primary component of plankton...
s, but the structure of the rest of the cell is different, so it may be that they are a separate line whose chloroplasts are derived from similar endosymbionts.
The cells typically have two slightly unequal
flagellaA flagellum is a tail-like structure that projects from the cell body of certain prokaryotic and eukaryotic cells, and functions in locomotion. There are some notable differences between prokaryotic and eukaryotic flagella, such as protein composition, structure, and mechanism of propulsion...
, both of which are smooth, and a unique organelle called a
haptonema, which is superficially similar to a flagellum but differs in the arrangement of
microtubuleMicrotubules are one of the components of the cytoskeleton. They have a diameter of 25 nm and length varying from 200 nanometers to 25 micrometers. Microtubules serve as structural components within cells and are involved in many cellular processes including mitosis, cytokinesis, and vesicular...
s and in its use. The name comes from the
GreekGreek , an independent branch of the Indo-European family of languages, is the language of the Greeks. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. In its ancient form, it is the language of classical...
hapsis, touch, and
nema, thread. The
mitochondriaIn cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5–10 micrometers in diameter...
have tubular
cristaCristae are the internal compartments formed by the inner membrane of a mitochondrion. They are studded with proteins, including ATP synthase and a variety of cytochromes. The maximum surface for chemical reactions to occur is within the mitochondria...
e.
Economic importance
Haptophytes are economically important as
Pavlova lutheri and
IsochrysisIsochrysis is a haptophyte genus.It includes the species Isochrysis galbana....
sp. are widely used in the
aquacultureAquaculture is the farming of freshwater and saltwater organisms such as finfish, molluscs, crustaceans and aquatic plants. Also known as aquafarming, aquaculture involves cultivating aquatic populations under controlled conditions, and can be contrasted with commercial fishing, which is the...
industries.
Examples and classification
The best-known haptophytes are
coccolithophoreCoccolithophores are single-celled algae, protists and phytoplankton belonging to the division haptophytes. They are distinguished by special calcium carbonate plates of uncertain function called coccoliths , which are important microfossils...
s, which have an exoskeleton of calcareous plates called
coccolithCoccoliths are individual plates of calcium carbonate formed by coccolithophores which are arranged around them in a coccosphere.- Formation and composition :...
s. Coccolithophores are some of the most abundant marine phytoplankton, especially in the open ocean and are extremely abundant as microfossils. Other planktonic haptophytes of note include
ChrysochromulinaChrysochromulina is a haptophyte genus.It includes the species Chrysochromulina ericina....
and
PrymnesiumPrymnesium is a haptophyte genus.It includes the species Prymnesium parvum....
, which periodically form toxic marine
algal bloomAn algal bloom is a rapid increase in the population of algae in an aquatic system. Algal blooms may occur in freshwater as well as marine environments. Typically, only one or a small number of phytoplankton species are involved, and some blooms may be recognized by discoloration of the water...
s, and
Phaeocystis blooms of which can produce unpleasant foam which often accumulates on beaches. Both molecular and morphological evidence supports their division into five orders; coccolithophores make up the Isochrysidales and Coccolithales.
Haptophytes are closely related to
cryptomonadThe cryptomonads are a group of algae, most of which have chloroplasts. They are common in freshwater, and also occur in marine and brackish habitats. Each cell is around 10-50 μm in size and flattened in shape, with an anterior groove or pocket...
s.