Which of the following categories does Gonyaulax belong to?

Correct — B. Gonyaulax is a dinoflagellate, which is option (b).

Dinoflagellates are mostly marine, mostly photosynthetic protists with two flagella — one lying in a groove that girdles the cell, the other trailing behind it — and stiff cellulose plates in the cell wall.

Gonyaulax is the standard textbook example because it multiplies so fast that the sea turns red: the red tide. The toxins such a bloom releases can kill fish outright and can accumulate in shellfish.

Why the others are wrong

• (a)
  Chrysophytes — Chrysophytes are the diatoms and desmids. Their defining feature is a two-piece silica cell wall that fits together like a soap-box, and their deposits form diatomaceous earth. Gonyaulax has no silica wall.
• (c)
  Euglenoids — Euglenoids are mostly freshwater flagellates with a protein pellicle in place of a cell wall, and they can feed heterotrophically in the dark. Euglena, not Gonyaulax, is the example of that group.
• (d)
  Protozoans — Protozoans in the textbook scheme are the heterotrophic protists — amoeboid, flagellated, ciliated and sporozoan. Gonyaulax photosynthesises, so it belongs with the algal protists instead.

Kingdom Protista collects the single-celled eukaryotes, and the textbook divides it into four groups worth holding apart by one feature each.

Chrysophytes — diatoms, with silica walls that survive as diatomaceous earth.
Dinoflagellates — two flagella, cellulose plates, red tides, Gonyaulax.
Euglenoids — a protein pellicle, no cell wall, mixotrophic, Euglena.
Protozoans — heterotrophic, including Amoeba, Paramoecium and Plasmodium.

An item that names one organism is answered by the example attached to its group, so learn the group and its example as a pair.

Key facts

• Gonyaulax is a dinoflagellate and the standard example of a red tide organism.
• Dinoflagellates carry two flagella, one transverse in a girdling groove and one longitudinal.
• Chrysophytes include the diatoms, whose silica walls accumulate as diatomaceous earth.
• Euglenoids have a protein-rich pellicle instead of a cell wall.

Common traps

• Choosing protozoan because Gonyaulax is a single-celled swimmer, and missing that it photosynthesises.
• Mixing up chrysophytes, which are the diatoms, with the dinoflagellates.

No directly related past PYQ was found.