Seahorses Are Cuddly . . . In an odd, sharp-spiked way

These questions were sent in by a friend. I’m willing to take a guess at what his new hobby is . . .

1) How many varieties of Seahorses are there?
About 35. This List gives both the Latin and common names, as well as some photographs.

2) Which of the varieties are not endangered?
All but one; only one seahorse species, the Knysna Seahorse, Hippocampus capensis, is listed as endangered.

3) Of the varieties that are not endangered, which varieties are the most likely to survive in captivity?
Any Captive-Bred Seahorse has the most luck of surviving.

4) Of the varieties that are most likely to survive in captivity, what items are crucial to creating the most effective Ecosystem? (Live Rock, Coral, Plants, Algae, food, water temperature, water quality, lighting, etc…)
Decorate your tank with plentiful Caulerpa and other macro algae; build small clearings between algae "forests". Seahorses love to hold with their tails onto the vegetation, also they sleep in higher tank regions between the plants. Keep Temp. at 25°C. No special bright lights are needed. Flow pumps that circulate the water 2 to 4 time an hour work best.

5) What creatures are most likely to cohabitate and not threaten the captive seahorse? (Snails, crabs, slugs, fish, shrimp, anemones, etc…)
This Article best describes the ideal Tankmates for a seahorse.

Sources and other Recommended Readings :
Seahorse.org
Docslaw Seaworld
Kingdom of the Seahorse
The Conscientious Marine Aquarist
Saltwater Aquariums for Dummies