The Octocorallia

Octocorals represent one of two subclasses in the class Anthozoa. There are two orders of octocorals that are important on reefs. The order Alcyonacea, the soft corals, include the leather corals that may form mats several square meters across, as well as upright and mushroom-shaped colonies, all of which lack an internal skeleton of gorgonin (see below). Alcyonarians are very common on Indo-west Pacific reefs, but are essentially absent on western Atlantic reefs.

The order Gorgonacea include the gorgonian corals, (e.g., sea fans, sea rods & sea feathers). Gorgonians are most prominent on Caribbean reefs even though there are more species in the Indo-west Pacific. Gorgonian corals, like the alcyonarians, are composed of polyps with 8 pinnnate tentacles connected to each other by a common tissue (coenenchyme) which contains numerous microscopic, calcitic elements, the sclerites. Unlike the Alcyonaria, most gorgonian colonies are supported by a flexible rod composed of collagen-like protein (gorgonin) that allows the colonies to bend in current or waves. Both orders are an important component of the coral reef community in terms of abundance, biomass, as well as diversity. Although sclerites can occasionally form solid substrate, the primary contribution of this group to reef structure is the production of calcitic sediment by sclerite production.

Most gorgonians in the Caribbean region (including Florida and the Bahamas) are in the families Plexauridae and Gorgoniidae.The plexaurids

include many genera with cylindrical branches such as Eunicea and Pexaurella as shown below.

The gorgoniids are typically gorgonians with flattened branches, including sea fans (genus Gorgonia) and sea feathers (genus Pseudopterogorgia) as shown below.

Unusual Octocorals

Class Anthozoa - subclass Octocorallia - order Helioporaceae

Family Helioporidae (Blue Coral; Gk. helios, sun; L. porus, pore)

There is only one species remaining in this order and it is found only in the Indo-west Pacific. It is also the only octocoral that forms a massive aragonite skeleton. Moreover, the skeleton is blue although the blue color cannot be seen with the polyps expanded. Colonies may be encrusting or consist of semi-massive base from which a mass of branches or lobes arise.

The Family Tubiporidae (organpipe coral; L. tubus, tupe; porus, pore): is a specialized group of alcyonaceans that construct small tubes in which the polyps are situated. There is only one genus although several species have been named. All are restricted to the Indo-Pacific region. The colony forms rounded heads that may reach 1m or more in diameter. Each polyp has a ring of 8 feather-like (pinnate) tentacles as is typical of octocorals. They are green bluish, gray, white, or brown in color. The skeleton is bright red in color, and is solid, rather than being composed of sclerites. The colony structure is composed of vertical tubes resembling the arrangement of a pipe organ. The tubes are fused together at intervals by horizontal platforms.