Why are soft corals called Octocorallia?

This class is divided into two subgroups: the Octocorallia – so named because they have 8 tentacles around the mouth – include sea fans, sea pens and soft corals; the Hexacorallia – with multiples of 6 tentacles around the mouth – include stony corals, black corals, sea anemones, and others.

Does Octocorallia have internal skeletons?

Octocorallia (also known as Alcyonaria) is a subclass of Anthozoa comprising around 3,000 species of water-based organisms formed of colonial polyps with 8-fold symmetry. These organisms have an internal skeleton secreted by mesoglea and polyps with eight tentacles and eight mesentaries.

Where are Octocorallia found?

The many species of octocorals are found throughout the world’s oceans. Of the cold-water species the highest density has been found along deep shelves and on seamounts. Octocorals are also commonly associated with stony coral reefs, such as Lophelia pertusa reef complexes near Norway.

Are cnidarians invertebrates?

Cnidarians are aquatic invertebrates. They have tissues and radial symmetry. They also have tentacles with stingers. There are two cnidarian body plans: the polyp and the medusa.

What’s the difference between a coral and an Octocorallia?

Although commonly called “soft corals,” the Octocorallia are not close relatives of the Scleractinia , or “true corals” living today. Unlike true corals, which have hexaradial symmetry, octocorals have eightfold radial symmetry — count the tentacles on the polyps of this Muricea, from the Bahamas.

How are pennatulaceans different from other cnidarians?

Pennatulaceans are a specialized and morphologically distinct group of octocorallian cnidarians [5]. Unlike other octocorals, they are formed by a single large primary polyp, also known as the initial polyp or oozooid. The primary polyp is anchored into soft sediment by a proximal muscular peduncle.

What kind of habitat does an Octocorallia live in?

Distribution and Habitat. The Octorocallia usually live on solid ground. They occur from shallow water to more than 4000 m depth. Sea pens are an exception here, because they inhabit sandy or muddy soils. They occur all over the world, in all seas.

Where are the polyps located in a Cnidaria?

The primary polyp is anchored into soft sediment by a proximal muscular peduncle. The distal region of the primary polyp forms a rachis that contains a few or many secondary or daughter polyps, which arise laterally from the central unbranched rachis as autozooids (the larger feeding polyps) and siphonozooids (smaller polyps for water circulation).