Both desmids and diatoms are types of algae, but they have some key differences:

Desmids:

* Cell wall: Made of cellulose, with a characteristic two-lobed structure.

* Symmetry: Usually have bilateral symmetry, meaning they can be divided into two mirror-image halves.

* Reproduction: Primarily reproduce asexually through cell division.

* Habitat: Mostly found in freshwater, particularly in acidic, oligotrophic (nutrient-poor) waters.

* Chloroplasts: Have multiple, scattered chloroplasts, giving them a green appearance.

Diatoms:

* Cell wall: Made of silica (glass-like material), forming a hard, protective shell called a frustule.

* Symmetry: Have radial or bilateral symmetry.

* Reproduction: Primarily reproduce asexually through cell division, but also can reproduce sexually.

* Habitat: Found in freshwater and saltwater, including marine environments.

* Chloroplasts: Have one or two large, central chloroplasts, giving them a golden-brown color.

Here's a table summarizing the key differences:

| Feature | Desmids | Diatoms |

|--------------------|------------------------|--------------------------|

| Cell wall | Cellulose | Silica (glass-like) |

| Symmetry | Bilateral (mostly) | Radial or bilateral |

| Reproduction | Asexual (cell division) | Asexual & sexual |

| Habitat | Freshwater (mostly) | Freshwater & saltwater |

| Chloroplasts | Multiple, scattered | One or two, central |

In summary, desmids are distinguished by their cellulose cell walls, two-lobed structure, and preference for freshwater environments. Diatoms, on the other hand, are known for their silica frustules, various symmetries, and broader habitat range, including saltwater environments.