INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

PROTISTS - PROTISTA

PROTOZOA

ALVEOLATES

PHYLUM DINOFLAGELLATES (DINOPHYTA)

CLASS DINOFLAGELLATES (DINOFLAGELLATA)

Morphology. The Cell shape is spherical or elongated-oval; in many thecate species, the cell is flattened and bears projections (Fig. 30). A characteristic feature of theca is the presence of two intersecting grooves on the body: a longitudinal and a transverse one. The transverse groove divides the cell into two halves - upper and lower.

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Fig. 30. Dinoflagellates (a - from Hausmann; b - from Poliansky):

a - Ceratium hirudinella; b - Noctiluca miliaris: 1 - thecal valve; 2 - equatorial groove; 3 - Nucleus;

4 - short flagellum; 5 - cytoplasmic projection; 6 - food vacuole

Theca is absent in the groove regions, and the pellicle consists solely of the Plasmalemma. Pseudopodia capable of phagocytosis may form here. Two flagella of unequal length emerge from the intersection of the two grooves and perform different Functions: one lies in the transverse groove and acts as a locomotory organelle, while the other lies in the longitudinal groove and serves as a rudder. In some species, one flagellum (the longitudinal one) is partially or completely reduced. The Nucleus of dinoflagellates has a unique Structure: the Chromosomes lack Histones, which are characteristic of eukaryotic Nuclear Proteins. In addition, there are certain peculiarities in Chromosome structure.

Contractile vacuoles are absent, even in freshwater species. Regarding their Nutrition, they are predominantly autotrophs with brownish-yellow or green chromatophores, although heterotrophs also occur.

Reproduction. Dinoflagellates reproduce mainly by binary fission. Species with elastic pelicle inherit one half of the body along with the pellicle from the mother cell and regenerate the other half. Thecate species first shed their theca, after which the daughter individuals form new ones. A Sexual process in the form of isogamy or anisogamy has been discovered in some species.

In freshwater bodies, Ceratium hirudinella is frequently found with long thecal projections that increase the body surface area (Fig. 30, a). One of the flagella is directed far forward, while the other lies in the equatorial groove and moves in a wave-like manner. Other species of the genus Ceratium inhabit both fresh and marine waters and are often a major component of microplankton.

Among dinoflagellates, there are non-photosynthetic forms that have transitioned to heterotrophic nutrition. The sea sparkle (Noctiluca miliaris), up to 2 mm in diameter, is widespread in the plankton of warm seas, including the Black Sea (Fig. 30, b). It lacks a cellulosic theca and possesses only a single short flagellum, with locomotion instead performed by a long cytoplasmic projection. The Cytoplasm contains large, fat-filled vacuoles that reduce the specific gravity of the Organism. Noctiluca possesses a cell Mouth and food vacuoles, feeding on Protozoa and unicellular Algae. Upon mechanical stimulation (such as waves), it is capable of Bioluminescence, which is caused by The oxidation of a lipid-like substance, luciferin, by the enzyme luciferase, releasing light energy. During mass reproduction, these protozoa cause the luminescence of sea waves.

Many dinoflagellates are intracellular symbionts of Ciliates, radiolarians, hydras, stony corals, and other organisms. Notably, the mutualist of stony corals, Symbiodinium microadriaticum, facilitates The formation of their calcareous Skeleton.