Doc: Dinoflagellates, Red Tides NEET Notes | EduRev

Dinoflagellates - Protists With Two Flagella

• Dinoflagellates are mainly marine. They are found on the surface of the water. These are golden brown in colour.
  
  Dinoflagellates
• In Dinoflagellates, nutrition is mainly holophytic, because they have chloroplast.
  Example - Noctiluca, Ceratium, Gonyaulax, Gymnodinium, Pyrocystis.
• Ceratium - It is also an exception because its, mode of nutrition is mixotrophic.
• Noctiluca is an exception in Dinoflagellates because:
  (i) It is colourless.
  (ii) Chloroplast is absent.
  (iii) Photosynthesis is absent in it. Therefore, it has a holozoic mode of nutrition.
  (iv) But yet it is placed in Dinoflagellates because two flagella are present.
  (v) Plated cell wall is present.

Note: It is also classified in protozoa due to its holozoic mode of nutrition and colourless body.

• Their cell wall is divided into plates, which is made up of cellulose. Therefore the covering of Dinoflagellates is seen as armoured, so they are called as Armoured algae.
• Dinoflagellates have two flagella - one is transverse and other is longitudinal. Dinoflagellates show a special type of movement which is like whorling whips. Therefore they are also known as "Whorling whips".
  
  Parts of Dinoflagellates

• Dinoflagellates are haploid. Histone proteins are absent. Due to this reason Dinoflagellates are called as Mesokaryote.
• They have an osmoregulatory structure called 'Pusule'.
• Dinoflagellates are yellow-brown or golden brown in colour. These colour of Dinoflagellates are due to the pigments present in them - Chlorophyll 'a', Chlorophyll 'c' and Xanthophylls (Dinoxanthin & Didinoxanthin).
• They have starch as stored food.

➤ Reproduction

• Mainly Asexual – Binary fission.
• Sexual reproduction is very rare. Dinoflagellates are haploid, so they reproduce by Zygotic meiosis. Therefore, their life cycle is haplontic type.

Note: Exceptionally Noctiluca is diploid so it reproduce by gametic meiosis, therefore its life cycle is Diplontic type.

• They are found in different shapes such as circular, rectangular, triangular, elongated and boat-shaped.
• The cell wall of diatoms is made up of cellulose in which silica particles are embedded in many places, due to which the cell wall appears to be made up of silica. This silicate cell wall is called "shell" or "frustule".

• Their cell wall is made up of two halves, which are arranged like the lids of a soapbox. These half parts are collectively known as theca. The part which is present on the upper side acts as the lid and known as epitheca, and the other basal part is known as hypotheca. The place where the two parts overlap each other is called a girdle.

Note: Their cell wall has silica in very large quantity. Due to this reason, their cell wall is hard. The cell wall does not get destroyed after their death so, at the bottom of the sea, very huge rocks of dead diatoms are formed which are known as "diatomite" or "diatomaceous earth" or "kieselguhr".

• The diploid nucleus is present in Diatom.
  Diatom
• Their cells have chloroplasts, in which pigments are present, Chlorophyll 'a', Chlorophyll 'c', and xanthophyll (fucoxanthin). Due to these pigments, it appears golden coloured.
• Stored food: Leucosin (Chrysolaminarian) & fats (Oil).
• Movement: They are immotile because flagella are absent. They float on the surface of the water with the help of low molecular weight stored fats.

• Soundproofing
• Filtration of oils and syrups.
• Stone polishing.
• As "Heat insulator" in steam boilers, i.e. they are used as thermostat because the kieselguhr is a bad conductor of heat.