Bunaken National Park History Book

5. Marine Organisms

5.1 Algae

5.2 Forams

5.3 Sponges

5.4 Cnidarians

5.4.1 Corals

5.4.2 Anemones

5.4.3 Hydroids

5.4.4 Jellyfish

5.5 Marine Worms

5.6 Crustaceans

5.7 Echynoderms

5.7.1 Sea stars

5.7.2 Brittle stars

5.7.3 Sea Urchins

5.7.4 Sea cucumbers

5.7.4 (sic — 5.7.5) Feather stars

5.8 Molluscs

5.9 Ascidians

5. Marine Organisms

5.3 Sponges

Sponges were the dominant reef animals before corals existed. Sponges have been around for over half a billion years!

5.4 Cnidarians

5.4.1 Corals

Corals are colonies of animals called "polyps", joined together by a thin layer of common tissue.

Hard corals

Some species of branching Acropora can grow up to 15 cm per year while a massive Porities coral growns only about 3 mm per year. A three meter high Porities coral may be 1,000 years old!

Soft corals

5.4.3 Hydroids

Hydroids are a colony of animals that consists of two different types of polyps. One feeds and stings for defense agaisnt predators, and the other one reproduces. [...]
Generally, hydroids produce male or demale medusae (free swimming polyps) that break away and reproduce. [...]
The most common hydroids look like soft bunches of fine feathers attached to the reef. Other hydroids that have a hard calcareous skeleton look like hard corals and are known as fire corals and lace corals.

5.5 Marine Worms

Some flatworms mimic bad-tasting nudibranches as a form of protection from predators.