The marine microalgal class Bolidophyceae is a sister group to the diatoms and includes motile naked (bolidomonad) cells and nonmotile siliceous plate‐bearing (parmalean) cells. The bolidomonad cell possesses two unequal flagella, a long one bearing mastigonemes (tubular hairs) and a shorter smooth one, with the basal apparatus reduced to basal bodies. The parmalean cell wall is composed of 5–8 interlocking siliceous plates, which exhibit distinct dorsal, ventral, shield and girdle plate morphologies. Both cell types have a chloroplast (including the major carotenoid fucoxanthin and chlorophylls a+c1+c2+c3) with a girdle lamella, Golgi body, nucleus, mitochondrion and large vacuole. The group currently includes approximately 30 taxa, mostly described from high latitudes, although some tropical species also have been reported. Parmalean algae reach high absolute abundances in the spring, but later in the summer, they sink to the pycnocline (a layer of maximum water density difference) – a strategy similar to the centric diatoms. Their rare occurrences in sediment trap and surface sediments suggest that the siliceous plates are mostly recycled in the photic zone, yet plates of parmalean algae have been discovered in older sediments, although their true stratigraphic distribution remains unknown.

Key Concepts

  • Recent gene sequence analyses have shown that the genus Bolidomonas is polyphyletic, forming several clades, one of which includes the Parmales, resulting in all Bolidomonas species being transferred to Triparma.
  • The Bolidophyceae is a sister group to the diatoms, with similar cell features and pigment composition.
  • Bolidomonad cells are motile and naked, while the nonmotile parmalean cells are covered by 5–8 silicified plates, consisting of three or four types (shield, girdle, ventral and/or dorsal), arranged in a particular pattern and with distinct morphology, which defines each genus.
  • At present, the ploidy level or life cycle has not been identified; however, it is possible that the nonmotile silica plate‐bearing cells are diploid and alternate with a naked bolidomonad‐like flagellate haploid stage.
  • Naked bolidomonads appear to be present throughout the World's oceans, while most parmalean taxa inhabit high latitude areas, although tropical taxa also exist.
  • Studies have shown the parmalean ecology is similar to that of the centric diatoms, with assemblages remaining in their silicified form throughout the year and sinking to the pycnocline in the summer.
  • Remains of parmalean cells found in the fossil record suggest at least an early Cenozoic origin.
  • If the bolidophytes are haplodiplontic and represent an ancestral stage to the diplontic diatoms, then future molecular clock calculations should reveal a much older origin, possibly as old as the late Paleozoic (as diatoms are believed to have diverged around the Permian–Triassic boundary).

Keywords: marine; microalgae; plates; plankton; silica

Figure 1. (a) Schematic diagram of a sectioned parmalean cell. Marchant and McEldowney, , Figure 11. Reproduced with permission of Springer Nature. (b) Schematic diagram of a sectioned bolidomonad cell. Guillou et al., , Figure 1. Reproduced with permission of Allen Press.
Figure 2. (a) Four parmalean taxa of different sizes (St. KNOT, KH99‐3, western North Pacific, 60 m). (b) Two cells of Tetraparma pelagica, one with (arrow) and other without central spines (St. KNOT, KH99‐3, western North Pacific, 60 m). (c) Cell of T. pelagica showing one shield plate missing, exposing the flanges (arrow) of the surrounding plates (St. 19, KH07‐4, Southern Ocean, surface water). (d) Collapsed cell of T. pelagica showing exposed flanges of several plates and the hole at the end of one of the arms of the dorsal plate (arrows) (St. 19, KH07‐4, Southern Ocean, surface water). Konno and Jordan . Reproduced with permission of John Wiley & Sons.
Figure 3. Siliceous plate configurations of Tetraparma pelagica showing (a) cell in dorsal view (St. 19, KH07‐4, Southern Ocean, surface water) and (b) cell in girdle view (St. 20, KH07‐4, Southern Ocean, surface water), and of Triparma columacea subsp. alata showing. (c) Cell in shield view (St. 19, KH07‐4, Southern Ocean, surface water) and (d) cell in girdle view (St. 20, KH07‐4, Southern Ocean, surface water). d = dorsal plate, g = girdle plate, s=shield plate, v=ventral plate. Konno and Jordan . Reproduced with permission of John Wiley & Sons.
Figure 4. Examples of tropical parmalean taxa: (a) Tetraparma insecta (St. PA01, 124 m, Sulu Sea), (b–c) Tetraparma silverae (St. PA11, 100 m, South China Sea), (d) Tetraparma trullifera (St. PA01, 101 m, Sulu Sea), (e) Triparma columacea f. longiseta (St. PA01, 124 m, Sulu Sea), (f) Triparma laevis f. mexicana (St. PA01, 101 m, Sulu Sea), (g) Triparma laevis f. fusiformis (St. PA11, 100 m, South China Sea), (h) Triparma retinervis f. tortispina (St. PA11, 100 m, South China Sea). Fujita and Jordan . Reproduced with permission of Taylor and Francis.
Figure 5. Examples of each of the three parmalean genera and their plate configurations: (a) Pentalamina corona (St. 3, KH07‐4, Southern Ocean, surface water), (b) Plate configuration of Pentalamina, (c) Tetraparma pelagica (St. 20, KH07‐4, Southern Ocean, surface water), (d) Plate configuration of Tetraparma (showing left‐handed and right‐handed rotations of the girdle plates), (e) Triparma columacea subsp. alata (St. 19, KH07‐4, Southern Ocean, surface water), and (f) Plate configuration of Triparma (showing some variation in the girdle plate design). Where d = dorsal plate, s = shield plate, g = girdle plate, and v = ventral plate. (a,c,e) Konno and Jordan . Reproduced with permission from Taylor and Francis.
Figure 6. (a) Filter with numerous parmalean cells (St. 337, Conrad 10, southern Bering Sea, surface water). (b) Combination cell with Tetraparma pelagica (upper) and T. gracilis (lower) (St. 3, KH07‐4, Southern Ocean, surface water). (c) Collapsed cell of T. pelagica, containing inside either an identical but incompletely formed cell cover or an unidentified life cycle phase (St. 337, Conrad 10, southern Bering Sea, surface water). (d–f) Zooplankton faecal pellets containing parmalean cells. (d) St. KNOT, KH99‐3, western North Pacific, 150 m. (a–d) Konno and Jordan . Reproduced with permission of John Wiley & Sons. (e) KAXIS station 39 – Southern Ocean, deep chlorophyll maximum, 30 m. (f) Southern Ocean Time Series, sub‐Antarctic zone, 35 m. (e, f) Courtesy of Australian Antarctic Division.


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Further Reading

Kristiansen J and Preisig HR (eds) (2001) Encyclopedia of Chrysophyte Genera. Bibliotheca Phycologica 110: 1–260.

Kuwata A and Jewson DH (2015) Ecology and evolution of marine diatoms and Parmales. In: Ohtsuka S et al. (eds) Marine Protists, pp 251–275. Springer: Japan.

Marchant HJ and Scott FJ (2005) Chrysophytes. In: Scott FJ and Marchant HJ (eds) Antarctic Marine Protists, pp 295–307. ABRS and AAD: Canberra and Hobart, Australia.

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Jordan, Richard W, Fujita, Ryohei, Konno, Susumu, and Eriksen, Ruth(Sep 2019) Bolidophyceae. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0023691.pub2]