Hammer Corals

What are hammer corals?

Hammer corals are large polyp stony corals in the genus Euphyllia, named for tentacle tips that flatten into a hammer, anchor, or kidney shape. The wall form is Euphyllia ancora and the branching form is Euphyllia parancora. Both keep their tentacles extended through the day, so a colony is in constant motion under gentle flow. Along with torch and frogspawn they form the core of the Euphyllia group that most reefers build a mixed reef around.

Hammer coral morphs and lineages

Hammers are traded on tip color and contrast, and named lineages hold their value well:

• Gold and golden hammer — warm yellow-gold tentacles, one of the most consistently in-demand morphs and a strong value colony builder.
• Hologram hammer — multi-tone tentacles that shift color across their length, producing a shimmering effect under blue-heavy lighting.
• Rainbow and grail morphs — lineages carrying three or more distinct colors across the tips and body, priced at the top of the group.
• Bicolor, plum, and splatter morphs — two-tone tips or contrasting speckling, offering strong visual impact at a more accessible price.

Hammer coral care: light, flow, and stability

Moderate light and gentle, indirect flow are the targets, with stability mattering more than any single number. A hammer builds skeleton continuously, so alkalinity and calcium swings show up quickly as retracted heads or tissue recession; track them with reliable water testing equipment and check your reef lighting coverage before moving a colony up the rockwork. Avoid placing a hammer in direct powerhead flow, which folds the tentacles back and abrades tissue at the skeletal edge.

Spacing hammers in a mixed reef

Hammer sweepers reach several inches after dark, and the damage they do usually appears before the cause is identified. Watch the tank an hour after lights out to see the real footprint, then leave six inches or more between a hammer and any non-Euphyllia coral. Account for growth too: a branching hammer adds heads outward year over year, so a gap that looks generous today can close within a season. Keep hammers clear of chalices in particular, which reach even further.

Growing a Euphyllia garden

Hammers are the usual foundation of a Euphyllia garden, with torch and frogspawn filling in around them for contrast in tentacle shape. Compare torch corals and frogspawn corals, see the whole genus together in Euphyllia corals, or look through established multi-head pieces in coral colonies.