to Jassybio13
Sorry for the late reply, sometimes the internet flumxes me.
1. The only way that I have found is to spawn them and the males put out white gametes and the eggs of the female are yellowish, but even then to be sure it is best to check them out under a microscope. Then the males and females can be kept separately.
2, Rearing the larvae is difficult. I have used 5 species but now only 3, Rhodomonas lens, Isochrysis gabena, and Chaetosous gracillas. Rhodomonas is the critical one. (sorry about the spelling)
3. In my experience, the adults are from about 4 to 7 cm test diameter. The larval stage is typically from 38 to 50 days, there is a lot of variation in culture in the larval period probably due to variations in physical and nutritional factors during the larval period.
4. On spawning, I find that keeping the adults at 25 C as a constant temperature with ample food keeps them in spawning condition, the when a spawn is needed, a tray of warm water, about 30 C is prepared as is a holding tank at ambient temperature. The adults are placed in the tray, the males usually spawn almost immediately, the females follow either very soon or sometime as long as 30 minutes later. The males are kept in the spawning tray for a short time 5 to 10 minutes and then transferred to the holding tank where they continue to spawn. Females are also transferred but sometimes as long as 15 minutes later. Sometimes the females spawn in the holding tank as well. The eggs are very tiny, only 80 microns and they are sieved out with 20 or 35 micron nylon mesh.
It's not an easy task, I would recommend going with a different species at first to gain the experience needed to work with Diadema.