Luminous Organs of the Deep-Sea Squaloid Shark, 
Centroscyllium ritteri Jordan and Fowler 
Tamotsu Iwai 1 
In THEIR world-wide revision of the squaloid 
sharks, Bigelow and Schroeder (1957: 47) re- 
ferred five species to the genus Centroscyllium, 
viz.: ritteri, 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 in- 
habit rather great depths, very little regarding it 
has been reported. Except for the lower denti- 
tion, the taxonomic features of Centroscyllium 
resemble those of Etmopterus, which is known 
to possess a number of minute luminous or- 
gans, particularly in a blackish color pattern. 
The present study was made in order to deter- 
mine whether C. ritteri, like the species of 
Etmopterus, possesses luminous organs. 
In regard to the luminous organs of Etmop- 
terus, 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 lumi- 
nous organs of C. ritteri nor a comparison of 
them with those of species of the genus Etmop- 
terus have hitherto been presented, though 
Burckhardt (1900: 567) briefly dealt with the 
luminous organs in certain species of Centro- 
scyllium . 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 appre- 
ciation 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 manu- 
script 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. 
1 Department of Fisheries, Kyoto University, Mai- 
zuru, Japan. Manuscript received July 29, 1958. 
MATERIAL AND METHODS 
Since C. ritteri is relatively rare, only a single 
specimen measuring 160 mm. from the tip of 
snout to the origin of upper lobe of caudal fin, 
and 216 mm. in total length, was available for 
a dissection. It has been preserved in 10 per 
cent formalin. The distribution of the luminous 
organs was first examined by means of a binoc- 
ular microscope. Then the skin was removed 
for the microscopic preparations. Sections were 
made by the usual paraffin method at a standard 
thickness of 10 /*. The staining methods used 
were Mayer’s hemalum-eosin and Mallory’s triple 
stains. 
In order to make a comparison of the lumi- 
nous organs an embryo of Etmopterus lucifer 
Jordan and Snyder measuring 135 mm. in total 
length was also sectioned. 
OBSERVATIONS AND DESCRIPTIONS 
Distribution of the Luminous Organs 
The luminous organs of C. ritteri are widely 
distributed over the body surface and some 
of the fins, though gradation is not uniform 
throughout the body. The organs are so num- 
erous that their total number is difficult to esti- 
mate. Each organ is very small, 0.11-0.15 mm. 
in diameter, and is provided with a pigment 
sheath. In addition, these sink within the epi- 
dermis. Therefore, it is scarcely possible to ob- 
serve the organs with the naked eye. However, 
they can be seen as small black spots under a 
low magnification. 
In general, the densely distributed areas of 
luminous organs agree well with the jet-black 
color pattern marked on the body. The ground 
color of the head and body preserved in formalin 
is chocolate brown, but the tip and ventral sur- 
face of head are black, as is the belly. The first 
and second dorsal fins and the pectoral fin are 
edged with a white band. There are distinct 
black markings on the ventral surface of the 
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