Coralline is a kind of hard, encrusting algae that is commonly found on coral reefs. It is also found in the marine aquarium on live rock. Some echinoderms (starfish and sea urchins) eat coralline. It is typically a deep purple color and slowly spreads across rock, glass and other surfaces. It is desirable in the home aquarium as it is very visually attractive. The algae (singular alga) comprise several different groups of living things that produce energy through photosynthesis. ... A Marine aquarium is an aquarium that keeps marine plants and animals in a contained environment. ... Live rock is a usually coralline rock with marine organisms living on or within the rock, and is a term used mainly in the aquarium trade. ... Classes Asteroidea Concentricycloidea Crinoidea Echinoidea Holothuroidea Ophiuroidea Echinoderms (Echinodermata) is a phylum of marine animals found in the ocean at all depths. ...