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The best answer for this quiz is to show you a video of the same specimens, made at higher magnification:

These are sea urchin sperm. Each adult sea urchin is either a male or a female, and can be induced to release gametes when ripe. Most developmental biology classes use urchins to obtain embryological material, and it is tremendously exciting to perform in vitro fertilizations. As you can see in this higher magnification video, each sperm has a head, containing the nucleus (DNA) and other organelles, and a long tail (flagellum) for swimming.

What is so amazing about the quiz video is that it was made by dipping a toothpick into the sperm sample, and putting the smallest possible amount of sperm on the microscope slide. The movie is then showing only a very small region of the slide, and represents a tiny sample of what an individual male urchin can release. The numbers are mind-boggling.

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