¹Faculty of Letters, Keio University, 4-1-1 Hiyoshi, Yokohama, 223-8521 Japan;
Present address: Hiroshima Prefectural Institute of Science and Technology, 3-10-32 Kagamiyama, Higashi-hiroshima, 739-0046 Japan
²Hayama Shiosai Museum, 2123-1 Isshiki, Hayma, 240-0111 Japan
³Uozu Aquarium, 1390 Sanga, Uozu, 937-0857 Japan
⁴School of Biosphere Sciences, Hiroshima University, Higashi-hiroshima, 739-8528 Japan

^*Corresponding author: School of Biosphere Sciences, Hiroshima University, 1-4-4 Kagamiyama, Higashi-hiroshima, 739-8528, Japan; tel.: +81 824 24 7986; FAX: +81 824 22 7059; E-mail takn@hiroshima-u.ac.jp

Abstract

  Colonies of the 'big mouth' tunicate, Megalodicopia hians, were first discovered in Toyama Bay, Japan Sea. The suspension-feeding habit of this organism is inferred from the diets in the oral aperture and feces. The colonies were mainly found on the steep slope (water depth >1 km), particularly at the sites characterized by exposed rocks and/or thin sediment. Most of the individuals faced 'mouth' downward, suggesting that they trap suspended matters adrift or re-suspended sediment in the upward current. We have analyzed the composition of total fatty acids of Megalodicopia hians in comparison with those of other bathyal benthic animals having various feeding habits and phylogenies. A dendrogram was constructed by the cluster analysis of the fatty acid compositions. Primary grouping in the fatty acid-based dendrogram reflected the feeding habits rather than the phylogenic relationships of the studied benthic animals. An inference from the dendrogram suggested usual suspension-feeding but occasional scavenging habit of this organism, in general agreement with the inference from the diet analysis.