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Haptophyte

life science Maturity 11-13 Next article →

Haptophytes are a diverse clade of algae capable of producing minerals. They are known by several names, including Haptophytina, Haptophyta, or Prymnesiophyta. Some scientists use the names Haptophyceae or Prymnesiophyceae to classify them at the class rank. While scientists have improved their understanding of haptophyte phylogenetics, there is still debate regarding the most appropriate classification rank. These organisms are essential components of marine ecosystems, playing major roles in the ocean's biological processes.

2023 Haptophyte
2023 Haptophyte

The cellular structure of a haptophyte is quite distinct. Their chloroplasts, which are the parts that allow for photosynthesis, contain chlorophylls a, c1, and c2, but they lack chlorophyll b. These cells also contain various carotenoids, specifically beta-, alpha-, and gamma- carotenes. A key pigment is fucoxanthin, an oxidized isoprenoid derivative. This specific pigment is likely the main reason these algae appear brownish-yellow. Their mitochondria feature tubular cristae, which are internal folds of the mitochondrial membrane.

2023 Haptophyte
2023 Haptophyte

Movement and energy storage are central to how haptophytes function. Most cells possess two slightly unequal, smooth flagella used for swimming. They also feature a unique organelle called a haptonema. The name comes from the Greek words *hapsis*, meaning touch, and *nema*, meaning thread. While it looks like a flagellum, the haptonema has a different arrangement of microtubules and serves a different purpose. For energy, most haptophytes store chrysolaminarin in membrane-bound vacuoles within the cytoplasm. This polysaccharide has a short chain length of 20 to 50 glycosides. In contrast, the comparable amylose has chains of over 300 units. Some members of the Pavlovaceae family produce a different substance called paramylon.

Classification of these algae has evolved through scientific discovery. Originally, researchers placed haptophytes in the class Chrysophyceae, known as golden algae. However, new ultrastructural data provided evidence that they belong in a separate group. Molecular and morphological evidence now supports dividing them into five distinct orders. Many scientists have contributed to this complex taxonomic history. For example, Hibberd used the name Haptophyta in 1976. Cavalier-Smith has also provided significant classifications in 1986 and 2015.

2023 Haptophyte
2023 Haptophyte

The most significant group within this clade is the coccolithophores. They represent 673 of the 762 described haptophyte species. These organisms create an exoskeleton made of calcareous plates called coccoliths. Coccolithophores are among the most abundant marine phytoplankton, particularly in the open ocean. They are also extremely abundant as microfossils. Over vast periods of time, these tiny remains have formed large chalk deposits. This makes them a vital part of the geological record.

2023 Haptophyte
2023 Haptophyte

Other haptophytes have notable impacts on the environment and human industry. Some species, such as *Chrysochromulina* and *Prymnesium*, can form toxic marine algal blooms. Another genus, *Phaeocystis*, can create blooms that produce unpleasant foam on beaches. From an economic perspective, haptophytes are very important to the aquaculture industry. Species like *Pavlova lutheri* and *Isochrysis sp.* are used to feed shrimp and oyster larvae. These algae are rich in polyunsaturated fatty acids. These include docosahexaenoic acid (DHA), stearidonic acid, and alpha-linolenic acid. Additionally, *Tisochrysis lutea* contains phospholipids and betain lipids.

2023 Haptophyte
2023 Haptophyte

Haptophytes are also linked to broader biological groups and tiny ecological players. Very small, uncultured pico-prymnesiophytes, measuring only 2 to 3 micrometers, are ecologically important. Scientists have discussed haptophytes being closely related to cryptomonads. They are also considered closely related to the SAR clade. This connection helps researchers understand the wider tree of life. By studying these tiny organisms, we learn more about how life functions in the sea.

2023 Haptophyte
2023 Haptophyte
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