Algal divisions and motility: which group never forms flagellated cells? Among the major algal divisions, identify the group in which no member produces motile, flagellated cells at any stage of the life cycle.

Introduction / Context:
Motility is a helpful diagnostic character in phycology. Many algal lineages produce flagellated gametes or spores, but one major division is entirely without flagella at every stage—an important memory anchor for classification questions.

Given Data / Assumptions:

• Question asks for a division with no flagellated cells.
• We consider common textbook divisions used in introductory phycology.
• We focus on life-history stages (gametes, spores) as well as vegetative cells.

Concept / Approach:
Red algae (Rhodophyta) never produce motile, flagellated cells. Fertilization occurs via non-motile spermatia. By contrast, many green algae (Chlorophyta) and brown algae (Phaeophyta) form flagellated zoospores or gametes, while many chrysophytes and euglenoids are motile at least in some stages.

Step-by-Step Solution:
Recall hallmark: red algae lack flagella entirely.Check other divisions: green and brown algae commonly produce motile cells.Chrysophytes/diatoms may have flagellated stages (for example, male gametes in some brown algae relatives) or motile cells in related groups.Therefore select Rhodophyta.

Verification / Alternative check:
Standard life-cycle diagrams for Polysiphonia and other reds show non-motile spermatia and no flagella, confirming the rule of thumb: “Rhodophyta never have flagella.”

Why Other Options Are Wrong:

• Chlorophyta: many genera form flagellated zoospores/gametes.
• Phaeophyta: produce biflagellate reproductive cells.
• Chrysophyta/Euglenophyta: numerous members are flagellated or have motile stages.

Common Pitfalls:
Assuming diatoms are never motile. While vegetative diatoms glide rather than swim, motile stages exist in related heterokonts; the question asks for a division with absolutely no flagella—only Rhodophyta fits.

Final Answer:
Rhodophyta (red algae).