Dinoflagellates
Dinoflagellates are golden brown photosynthetic protists, belonging to class Dinophyceae (Pyrrophyta). They are mainly marine, though few are fresh water forms. They may appear red, yellow, green, brown or blue depending upon the main pigment present in cell.
General characters of dinoflagellates are as follows :
1.Unicellular , motile, biflagellate, golden brown photosynthetic protists (some are non-motile, amoeboid, plamelloid or filamentous).
- They are mostly marine, some are found in fresh water.
- The body is enclosed by a rigid coat called theca or lorica consisting of 2 to many articulated of sculptured plates of cellulose and pectin, hence are also called armoured dinoflagellates.
- Theca has generally two grooves i.e., longitudinal called sulcus and transverse called cingulum or annulus or girdle.
- Flagella are heterokont (different). One is longitudinal and other is transverse. The flagella pass out through the pores in the lorica and lie in the grooves. The transverse flagellum lies in the circular groove and the longitudinal flagellum in the longitudinal groove. The longitudinal flagellum is narrow, smooth directed posteriorly and the transverse flagellum is ribbon like.
- Most of the species have brown, green or yellow chromatophores with chlorophyll a ,c, -carotene, xanthophylls (e.g., Peridinin). Plasids are generally surrounded by 3-membrane envelope and contain 3- thylakoid lamellae. They are autotrophic or photosynthetic (Ceratium ), a few are saprobic or parasitic.
- Reserve food is carbohydrate and oils.
- Nucleus is relatively larger in size, has condensed chromosomes even in interphase, chromosomes do not have histone. Nuclear envelope and nucleolus remain present even during cell division. this organization is called Mesokaryon (Dogge, 1966).
- A non-contractile vacuole called pusule is present near the flagellar base. It may have one or more vesicle and takes part in floatation and osmoregulation.
- Some dinoflagellaes possess trichocysts and cnidoblasts like those of coelenterates.
- Reproduction is commonly asexual and occurs through cell division.
- Isogamous and anisogamous sexual reproduction is reported from some dinoflagellates e.g., Ceratium.
- Life cycle involves zygotic meiosis (Ceratium , Gymnodinium). Gametic meeisosi occurs in Noctiluca.
