Luminous Organs of the Deep-Sea Squaloid Shark, Centroscyllium ritteri Jordan and Fowler

IN THEIR world -wide revision of the squaloid sharks, Bigelow and Schroeder ( 1957: 47) referred five species to the genus Centr oscyllium, viz.: riiteri, granulatum, fabricii , nigrum, and ornatum. Of these, one species only, C. ritteri Jordan and Fowler, is recorded from the western Pacific region. Since this species appears to inhabit rather great depths, very little regarding it has been reported. Except for the lower dentition, the taxonomic features of Centroscyllium resemble those of Etmopterus, which is known to possess a number of minute luminous organs, particularly in a blackish color pattern. The present study was made in order to determine whether C. ritteri, like the species of Etmopterus, possesses luminous organs . In regard to the luminous organs of Etmopterus, there is sufficient literature to make an accurate review (e .g., Dahlgren and Kepner, 1908: 134; Ohshima, 1911: 1; Schmidt, 1931: 9). But neither detailed accounts of the luminous organs of C. ritteri nor a comparison of them with those of species of the genus Etmopterus have hitherto been presented, though Burckhardt (1900: 567) briefly dealt with the luminous organs in certain species of Centroscyllium. Such a comparison should both extend our knowledge of luminescence in elasmobranch fishes and afford a clearer insight into the nature of their luminous organs . The author wishes to express sincere appreciation to Prof. K. Matsubara for his cordial guidance and for permission to work on his collection . Thanks are also due to Dr. W . C. Schroeder of the Woods Hole Oceanographic Institution, for a critical review of the manuscript and for furnishing a copy of Burckhardt's paper. The comments and suggestions of Dr. Y. Haneda of the Yokosuka City Museum are gratefully acknowledged.