Alcyonacea is an sub-order of [Octocorallia](Octocorallia.md) itself order of [Anthozoa](Anthozoa.md). It regroup soft and hard corals that doesn't need light to grow. Those animals doesn't have (or have less) zooxanthellae, an [Algae](Algae.md) that is use to create a photosynthetic symbiosis in other [Octocorallia](Octocorallia.md).