Dinoflagellates are armoured algae.
They cause red tides which may lead to death of many of the aquatic lives.

**Armoured Algae:**

Armoured algae are a group of photosynthetic organisms that possess a protective covering. This protective covering, known as an armor, is composed of various materials that help to shield the algal cell from external factors such as predation and desiccation. Armoured algae can be found in various aquatic environments, including freshwater and marine habitats.

**Types of Armoured Algae:**

There are several types of armoured algae, each belonging to different taxonomic groups. Let's explore the possible options:

**a. Dinoflagellates:**
Dinoflagellates are a group of unicellular organisms that are commonly found in marine environments. They possess two flagella that enable them to move through the water. Some dinoflagellates have an armor-like structure called a theca, which is composed of cellulose plates. The theca provides protection and maintains the shape of the cell. Armoured dinoflagellates are known for their diverse forms and ecological importance.

**b. Euglenoids:**
Euglenoids are another group of unicellular organisms that can be found in freshwater environments. They possess a unique structure known as a pellicle, which acts as their armor. The pellicle is composed of proteinaceous strips called pellicle strips. These strips provide rigidity to the cell and protect it from mechanical stresses. Armoured euglenoids are known for their ability to change their shape and swim using a whip-like appendage called a flagellum.

**c. Red Algae:**
Red algae, also known as Rhodophyta, are multicellular organisms that primarily inhabit marine environments. They possess a cell wall composed of cellulose and other polysaccharides. This cell wall acts as their armor, providing protection and structural support. The red pigments present in their cells allow them to absorb light efficiently for photosynthesis. Armoured red algae are diverse in form and can be found in various marine habitats, from shallow waters to deep-sea environments.

**d. Cyanobacteria:**
Cyanobacteria, also known as blue-green algae, are a group of photosynthetic bacteria. While some cyanobacteria do not possess an armor, certain species have a protective outer layer called a sheath. This sheath is composed of a gelatinous substance that helps to protect the cyanobacterial cell from desiccation and grazing by other organisms. Armoured cyanobacteria are often found in freshwater environments, forming slimy mats or colonies.

In conclusion, armoured algae can belong to different taxonomic groups, including dinoflagellates, euglenoids, red algae, and cyanobacteria. Each group possesses a unique armor-like structure that provides protection and support to the algal cell.