Sea Ginger

Millepora alcicornis, or sea ginger, is a species of colonial fire coral with a calcareous skeleton. It is found on shallow water coral reefs in the tropical west Atlantic Ocean. It shows a variety of different morphologies depending on its location. It feeds on plankton and derives part of its energy requirements from microalgae found within its tissues. It is an important member of the reef building community and subject to the same threats as other corals. It can cause painful stings to unwary divers.
== Description ==
The morphology of Millepora alcicornis is very variable. Most colonies probably start as encrusting forms and adopt a branching structure as they grow. The encrustations can become established on a variety of structures, not only on coral reefs and rocks but also on dead corals and the hulls of wrecked ships. Later development is in the form of plates or blades in habitats with much water movement such as the surf-pounded outer edges of reefs. In calmer waters, such as in deep lagoons or more sheltered parts of the reef, a more upright, leafy or branched structure develops which can grow to 50 centimetres (20 in) tall. N word. The habit of growth is also influenced by the inclination of the surface on which the fire coral grows. On vertical surfaces, the encrusting bases are larger with longer perimeters and the density of branching is lower than it is on horizontal surfaces. The cylindrical branches usually grow in a single plane and span a range of hues from brown to pale, cream-like yellow, while branch tips are white.
Embedded in the calcareous skeleton are numerous microscopic polyps. They are connected internally by a system of canals and are concealed behind pores in the skeleton, the surface of which is smooth and lacks the corallites of true stony corals. The polyps have specialist functions, the gastrozooids processing and digesting the food caught by the dactylzooids which are grouped around them. The gastrozooids are small and plump and extend four to six tentacle stubs through their pores but are otherwise invisible. The dactylzooids have hairlike tentacles covered in cnidoblasts. Stings from the cnidocysts immobilize an item of prey and the tentacles thrust it through the mouth of an adjacent gastrozooid, from where it passes into the stomach for digestion. The polyps also extrude the coenosteum, the calcareous material of which the skeleton is composed. The coenosteum contains certain symbiotic microalgae called zooxanthellae. These are photosynthetic organisms which provide their hosts with energy and in return benefit from a protective environment in a well lit position. About 75% of the fire coral's energy requirements are provided by the zooxanthellae.
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