In this paper we examined the histology of three commercially valuable species of precious corals (Paracorallium japonicum, Corallium elatius, and C. konojoi) from the Ryukyu Archipelago. In order to observe their inner structure, samples were thin sectioned and examined with a digital light microscope. Colonies of C. konojoi had thicker coenenchyme and larger autozooids than those of C. elatius and P. japonicum. The sclerites of the three species tended to be concentrated in the outer layers of coenenchyme. The gastric cavities of autozooids of all three species were found to be relatively empty. Some symbiotic polychates were observed in the axis of P. japonicum. As well, a zoanthid (Corallizoanthus tsukaharai) was often observed living on the coenenchyme surface of P. japonicum. It is hoped our observations will provide a good foundation of future study of Japanese Coralliidae corals. 1. Introduction Species in the genera Corallium and Paracorallium (Subclass Octocorallia, Order Alcyonacea, Family Coralliidae) are well known for their red or pink skeletons that have been used since antiquity for ornament, medicine, talismans, and currency. Therefore, they have long been known as “precious corals.” Precious corals have been harvested routinely from the Mediterranean Sea for at least 5,000 years and were taken even as long as 30,000 years ago or more. Products made from Corallium rubrum (Linnaeus, 1758) are recorded from a Stone Age monument approximately 25,000 years old in Germany [1], and precious corals and shells were found in ruins roughly 30,000 years old in Lausanne, Switzerland [2]. The first record of collecting precious coral in Japan is from 1812, when a fisherman found a precious coral entangled in his net off Muroto, Kochi Prefecture, and harvest continues to the present day in the Kochi, Kagoshima, and Okinawa regions. It is generally recognized that the biomass of precious corals has been decreased by over-fishing, but there is little information about the biology of species from Japanese waters. Some taxonomical studies about Japanese species have been published [e.g., [3–11]]. Regarding biological information, Grigg [12], Kosuge [1], and Iwasaki and Suzuki [13] have presented growth data. Ueno et al. [14], Iwase [15], and Nonaka et al. [16] have reported on the raising of precious coral in aquaria. Recently, Iwasaki [17] edited a comprehensive publication on scientific, cultural, and historical perspectives of Coralliidae corals. However, there have been no studies on the histology or anatomy of Japanese precious corals, except for
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