八放珊瑚亚纲（学名：Octocorallia），又名海鸡冠亚纲（Alcyonaria）是珊瑚纲的一个亚纲，大约有三千个不同的种属组成，都是水生生物。所有八放珊瑚均属于八放珊瑚亚纲，泛指所有有八只辐射对称触手的珊瑚虫，牠们全是滤食性动物，聚居在水流大的地方。八放珊瑚亚纲包括了蓝珊瑚、软珊瑚、海笔、柳珊瑚等各种不同生物，并分为海鸡冠目（Alcyonacea）、苍珊瑚目（Helioporacea）及海笔目（Pennatulacea）三个目。这些生物都有内骨骼。如同所有的刺胞动物，这些生物都有一个复杂的生命周期阶段：包括被当作浮游生物的能动阶段，以及其后缤纷的固定阶段。

Octocorallia (also known Alcyonaria) is a subclass of Anthozoa comprising around 3,000 species of water-based organisms formed of colonial polyps with 8-fold symmetry. It includes the blue coral, soft corals, sea pens, and gorgonians (sea fans and sea whips) within three orders: Alcyonacea, Helioporacea, and Pennatulacea. These organisms have an internal skeleton secreted by mesoglea and polyps with eight tentacles and eight mesentaries. As with all Cnidarians these organisms have a complex life cycle including a motile phase when they are considered plankton and later characteristic sessile phase.