Any of the granules, approximately 32 nm x 48 nm and consisting of highly aggregated phycobiliproteins, that are attached in arrays to the external face of a thylakoid membrane in algae of the phyla Cyanophyta and Rhodophyta, where they function as light-harvesting devices in photosynthesis. Excitation energy in the phycobilisome flows in the sequence: phycoerythrin, phycocyanin, allophycocyanin before passing to the antenna chlorophyll of photosystem II. [ http://www.ncbi.nlm.nih.gov/pubmed/11734882 GOC:jl http://en.wikipedia.org/wiki/Phycobilisome ]