Input (grade 10): On the other hand, there are over 77,000 well-identified species of air-breathing chelicerates, and there may be about 500,000 unidentified species.
Output (grade 12): Although only four marine species survive, all of them horseshoe crabs, there are over 77,000 species of air-breathing chelicerates, and there may be about 500,000 unidentified species.