trunculus often burrows into the sand, making it difficult to detect even by scuba divers. While (as described in the next section) Hexaplex arguably does not fit every textual description of the hillazon, nevertheless "Of the thousands of fish and mollusks that were studied to date, no other fish has been found that can produce the tekhelet color" which suggests that there is no more likely alternative species. Arguments against Hexaplex Trunculus The Talmud equates the colors of tekhelet and indigo, but also gives a practical test to distinguish between the two fabrics. Seemingly, since the color-producing compounds in Hexaplex trunculus and indigo are identical, no test should be able to distinguish them. However, according to Professor Otto Elsner, while Hexaplex and indigo have the same color-producing compound, they also contain other compounds which differ and may lead to a different response in the practical test. According to Professor Ziderman, the test consists of a chemical reduction reaction occurring when hydrogen is produced by decaying organic matter. Indigo (from a vegetable source) is more strongly reduced than the debrominated indigo found in snail tekhelet (assuming a blue-purple rather than pure blue tekhelet), leading to a different result to the test. The hillazon'''s body resembles the sea. This does not appear to be true of Hexaplex. Hexaplex supporters argue that when alive Hexaplex is well camouflaged and has a similar appearance to the sea floor, apparently due to algae which grow on its shell. This shell color can even be blue, similar to the sea. The hillazon has a "form like a fish", which a snail seemingly does not. Hexaplex supporters reply that its shell somewhat resembles a fish in shape. Similarly Maimonides, Tosafot, and Rashi say the Ḥillazon is a "fish" (דג), while Hexaplex is a snail rather than a fish. Hexaplex supporters argue that many forms of aquatic life (e.g., shellfish — of which sea snails would be an example) are also called "דגים" in Hebrew. The hillazon is said to come up from the sea once every 70 years. It is unclear what this is exactly referring to, but the Hexaplex has no such cycle. Hexaplex supporters note that elsewhere the Talmud makes clear that the hillazon was also hunted by normal methods at other times. Some sources say the reference to "70 years" does not imply a periodic cycle, but rather simply that this phenomenon is a