Dinoflagellata

Dinoflagellata , phylum (division) of unicellular, mostly marine algae , called dinoflagellates. In some classification systems this division is called Pyrrhophyta. There are approximately 2,000 species of dinoflagellates. Most have two flagella that lie perpendicular to one another and cause them to spin as they move through the water. Most have walls, or thecae, that are rigid and armorlike and sometimes take on fantastic shapes. The plates that make up these walls are actually located inside the plasma membrane rather than outside, as cell walls are. Some species are heterotrophic, but many are photosynthetic organisms containing chlorophyll a and chlorophyll c. The green of these chlorophylls may be masked by various other pigments. Still other species are symbionts, living inside such organisms as jellyfish and corals. Food reserves are largely starch.

Reproduction for most dinoflagellates is asexual, through simple division of cells following mitosis. They are unusual in that in each cell, the chromosomes remain compact between divisions, instead of stretching out into slender threads, as in most other organisms. The chromosomes are constricted at regular intervals and do not have centromeres, or fiber-attachment centers. There is no spindle, yet the very numerous chromosomes are divided equally at the time of mitosis .

The dinoflagellates are important constituents of plankton, and as such are primary food sources in warmer oceans. Many forms are phosphorescent; they are largely responsible for the phosphorescence visible at night in tropical seas. The phenomenon known as red tide occurs when the rapid reproduction of certain dinoflagellate species results in large brownish red algal blooms. Some of these organisms are highly toxic and can kill fish and shellfish and kill or weaken the animals (including humans) that eat them in their turn or, in some cases, are merely exposed to water containing the organisms.

Dinomastigota (Dinoflagellata) A phylum of mostly single-celled organisms classified in the kingdom Protoctista. They are abundant in the marine plankton; many are photoautotrophs, containing brown xanthophyll pigments in addition to chlorophyll. Dinoflagellates characteristically have two undulipodia (flagella) for locomotion and most have a rigid cell wall of cellulose encrusted with silica. Some species (e.g. Noctiluca miliaris) are bioluminescent.

dinoflagellates A division (Dinoflagellata) of protists that are heterotrophs but closely allied to brown algae and diatoms (they are sometimes classified as algae). Many have brown or yellow chromoplasts containing xanthophyll and chlorophylls a and c; others are colourless. Typically, dinoflagellates have two flagella, one propelling water to the rear and providing forward motion, attached just behind the centre of the body and directed posteriorly, the other causing the body to rotate and move forwards, forming a transverse ring or spiral of several turns around the centre of the body. Some dinoflagellates are naked, others are covered with a membrane or plates of cellulose. Many species are capable of emitting light, and these are the main contributors to bioluminescence in the sea. Most are planktonic, some in fresh water but most in marine environments, and some live in symbiosis with animals (e.g. the flatworm Amphiscolops, sea anemones, and corals) with which they exchange nutrients. Some are colonial. There are many species.