I don't think the snowflake ate your seahorse. Snowflake eels have flat molars that are designed for crushing shells of crabs, shrimp, etc. They are not generally fish eaters. That's not saying they won't pick off a lazy or unhealthy fish if the opportunity arises but if you are feeding him twice a week, I seriously doubt this is what happened to your horse. I'm thinking your seahorse died and your clean up crew did their job and disposed of the body.