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Velvet horn coral

Hydnophora rigida

Also known as Horn Coral, Spine Coral, Velvet Horn, Thorny Coral, Branch Horn Coral

SaltwaterCoral

Velvet horn coral (Hydnophora rigida)
NPS photo - Bryan Harry · Public domain

Care at a glance

Temperature
75–81°F
24–27°C
pH
8.1–8.4
Adult size
11.8 in
30 cm
Minimum tank
26 gal
100 L
Temperament
Mostly peaceful
Social behavior
Solitary
Swim level
Bottom
Diet
Photosynthetic
Difficulty
Medium
Breeding
Hard
Rarity
Common
Reef safe
Reef safe
Family
Merulinidae
Origin
Found on shallow reef slopes and lagoons across the Indo-Pacific, including the Red Sea, Indian Ocean, and western Pacific.

Overview

The velvet horn coral is a branching stony coral for a stable, brightly lit reef tank. It is best kept once you have some reef experience.

Did you know

The velvet horn coral's stinging sweepers are potent enough that hobbyists often keep it well away from prized colonies. That caution lasts until they learn exactly how far it can reach at night.

Caring for the velvet horn coral

Keep the velvet horn coral in a stable reef of at least 26 gal (100 L), with strong light and brisk flow. It grows as upright, antler-like branches and adds height quickly once settled.

Hold the water at 75 to 81°F (24 to 27°C) and a pH of 8.1 to 8.4. Keep calcium near 420 ppm and alkalinity at 8 to 11 dKH. It feeds mostly through photosynthesis but accepts tiny meaty foods.

After dark it extends sweeper tentacles up to 7 cm long, and they can kill or badly sting anything nearby. Give it at least 15 to 20 cm of clear space on all sides.

Good to know

Hydnophora rigida sits in the family Merulinidae. It is a small polyp stony coral that builds an aragonite skeleton and hosts zooxanthellae. The raised monticules on its branches are a defining trait of the genus, formed where the walls of neighboring corallites meet. Small cone-shaped bumps called hydnophores cover it and give the surface a velvety, thorny texture. Most aquarium colonies are bright neon green, though brown and cream forms exist. The tissue is thin and fuzzy, and the polyps extend a soft fur of tentacles during the day.

In the wild

The velvet horn coral lives on shallow reef slopes and in lagoons across the Indo-Pacific. Its range includes the Red Sea, the Indian Ocean and the western Pacific.

Common questions

What size tank does a velvet horn coral need?

A velvet horn coral needs at least 26 gal (100 L).

What temperature and pH does a velvet horn coral need?

A velvet horn coral is comfortable at 75–81°F (24–27°C) with a pH of 8.1–8.4.

What does a velvet horn coral eat?

A velvet horn coral feeds mostly through photosynthesis. It also accepts tiny meaty foods.

How big does a velvet horn coral get?

An adult velvet horn coral reaches about 11.8 in (30 cm).

Related species