Evolution & Systematics

The current knowledge concerning the octocoral systematic is very ambiguous and inadequate due to the lack of studies conducted on these corals. Present literature is often confusing and variable as there is insufficient understanding on the soft coral species. Descriptions of these corals in the species level are also lack in detail and illustrations. The lowest level of identification of these soft corals only reaches the genus level.

Phylum Cnidaria:

Cnidarians are tentacle-bearing invertebrates that are usually radially symmetrical. They possess stinging structures known as Cnidocytes which is a distinguishing characteristic of this phylum. The cnidarians exist in two main growth stages which are polyp (solitary) and medusa (free swimming) forms. Both forms comprise the outer layer which is the epidermis that bears sensory cells and the inner layer, the gastrodermis that is responsible for digestion and reproduction. Mesoglea, a third layer connects both the outer and inner layer.

      This phylum is split up into different classes that include the:

• Class Hydrozoa: Hydroids and stylasterine corals. This class is represented by both polyp-bearing and medusoid forms.

• Class Scyphozoa: The true jellyfish. This class mainly exists in free-swimming medusoid forms. However during their development, they are found attached by a stalk.

• Class Cubozoa: Box jellyfish. This marine jellyfish has a cubic bell shape hence the name of this class.

• Class Anthozoa: Soft and hard corals, sea pens, anemones and corallimorpharians. This class does not have the medusa stage and the polyps are mostly solitary or colonial.

Class Anthozoa:

This class is separated into different subclasses such as the:

• Subclass Hexacorallia: Sea anemones, hard corals and zoanthids. The polyps bear six or multiples of six tentacles without pinnules.

• Subclass Octocorallia:Soft corals, sea fans and sea pens. Each of the polyps comprise of eight hollow tentacles.

Subclass Octocorallia:

The subclass octocorallia is differentiated into different orders which are the:

• Order Helioporacea: Blue coral. The only octocoral that forms a massive aragonite skeleton like the hard corals.

• Order Pennatulacea: Sea pens. This group has a great diversity but lack in knowledge. Many species can be found in shallow water regions however majority lives in deep sea. They are usually characterised by the large, central axial polyp, known as the oozoid. This forms the penducle or foot of the colony and the autozooid and siphonozooid polyps.

• OrderAlcyonacea: This group is usually found in shallow waters of the Indian Ocean and Red Sea.

Family Alcyoniidae:

The colonies in this family are represented by the dominant reef-dwelling soft coral. Most colonies have a bare basal part and divided into lobed branches that bear the polyps. Some colonies have a flat upper surface.

Genus Cladiella:

Some colonies are mistaken as Sinularia or Klyxum. However, according to literature the lobes of Cladiella are shorter and more densely packed. The surface of the base does not feel rough as the sclerites are too minute. Nevertheless, in order to clearly identify the colonies, an examination on the sclerites can be carried out.

*The above information is retrieved from Ruppert, E Fox, R Barnes, R 2004, Invertebrate Zoology, 7^th edn, Brooks/Cole Cengage Learning, Belmont, USA and Fabricius, K & Alderslade, P 2001, Soft Corals and Sea Fans: A comprehensive guide to the tropical shallow-water genera of the Central-West Pacific, the Indian Ocean and the Red Sea, Australian Institute of Marine Science, Queensland, Australia.