Short answers, pulled from the story.
The scientific name of the spiny dye-murex snail is Bolinus brandaris. This medium-sized predatory sea snail lives in the eastern Mediterranean Sea and off the Atlantic coast of Morocco.
David Jacoby notes that twelve thousand snails of Murex brandaris yield no more than 1.4 grams of pure dye. That tiny amount is enough to color only the trim of a single garment.
Production of Tyrian purple for use as fabric dye began as early as 1200 BC by the Phoenicians. The name Tyrian refers to the city of Tyre in ancient Phoenicia, which is modern-day Lebanon.
By the fourth century AD, sumptuary laws in Rome had tightened so much that only the Roman emperor was permitted to wear Tyrian purple. A child born to a reigning emperor was said to be porphyrogenitos, or born in the purple.
The colored compound is 6,6'-dibromoindigo, an organic compound of bromine often found in algae and some sea life. Variations in colors relate to indigo dye, 6-bromoindigo, and red 6,6'-dibromoindigo.