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THE CARLSBERG FOUNDATION’S OCEANOGRAPHICAL EXPEDITION ROUND THE WORLD 1928-30 AND PREVIOUS “DANA’-EXPEDITIONS UNDER THE LEADERSHIP OF THE LATE PROFESSOR JOHANNES SCHMIDT DANA-BEPOBT No. 62. ■ RECTAL LIGHT ORGANS IN THE ARGENTINOID FISHES OPISTHOPROCTUS AND WINTERIA BY E. BERTELSEN AND OLE MUNK THE DANA OCEANOGBAPHICAL COLLECTIONS, CHARLOTTENLUND AND INSTITUTE OF COMPARATIVE ANATOMY AND ZOOLOGICAL TECHNIQUE, COPENHAGEN WITH 11 FIGURES IN THE TEXT AND 2 PLATES PUBLISHED BY THE CARLSBERG FOVNDATIOS THIS PAPER MAY BE REFERRED TO AS; .DANA-REPORT No. 62, 1984. COPENHAGEN ANDR. FKED. H0ST & SON PRINTED BY BIANCO Ll'NO A/S 1964 CONTENTS Introduction ..................................................................................................................................... 3 M aterial and m e th o d s.................................................................................................................. 3 A natom y of light and reflector o rg an s............................................................................... 4 A. Opisthoproctus soleatus and grimaldii................................................................... 4 1. The rectal b u lb ......................................................................................................... 4 2. The reflector o rg a n ................................................................................................. 6 B. Winteria telescopa........................................................................................................... 9 1. The rectal b u lb ......................................................................................................... 9 2. The reflector o rg a n ................................................................................................. 12 C. R elated a rg e n tin o id s.................................................................................................... 12 D isc u s sio n .......................................................................................................................................... 13 S u m m a ry ............................................................................................................................................ 16 L ite ra tu re ............................................................................................................................................ 17 INTRODUCTION Among the various types of luminous organs known in deep-sea fishes only a few can be definitely re- IX gardcd as derivatives of the mucous membrane of the alimentary canal (H a hm s 1928, K.vro 1947, H a n e d a 1950 & 1955). A preliminary report on the rectal bulb and the reflector organ of Opisthoproctus has been published by one of us (B e h t e i .s e n 1958). The present paper describes the histology of the rectal bulbs of the argentinoid fishes of the genera Opisthoproctus V a il l a n t *) and Winleria B h a u e h . The rectal bulbs of these two genera are luminous organs derived from the mucous membrane of the rectum. In both genera a reflector organ is situated in the ventral body wall, from which the light is emitted. Representatives of related genera have been examined but in none of these similar organs were observed^). The study is based on material from the Dana Oceanographical Collections. For the loan of specimens o f Rhynchohyalus natalensis (G il c h r is t and von B o n d e ) and of ^[nc^opinna microstoma C h a pm a n we ex­ press our gratitude to the Chicago Natural History Museum and the Smithsonian Institution, U.S. National Museum respectively. MATERIAL AND METHODS 1. Opisthoproctus soleatus V a ii.l a n t . A 12 mm long larva (standard length) from Dana st. 4006 II was embedded in paraffin, cut into 8 /* serial transverse sections, and stained with hematoxylin and orange G. One adult specimen, 42 mm long (standard length), from Dana st. 1181 IV was embedded in celloidin, cut into 50 ju serial transverse sections, and stained with M a l l o r y ’s phosphotungstic acid hematoxylin. Unstained celloidin sections of the rectal bulb of one adult specimen were made; the plane of sectioning was parallel to the median plane of the animal. Furthermore, the rectal bulb and the reflector organ of several larval and adult specimens were dissected. 2. Opisthoproctus grimaldii ZyGMAYER. Two larvae, 10 and 14.5 mm long, from Dana st. 4010 II and 4019 VII resp., were embedded in paraffin, cut into 8 serial transverse sections, and stained with E h r - l ic h ’s hematoxylin and eosin, hematoxylin and orange G, H e id e n h a in ’s azocarmine-aniline blue stain, PAS, Alcian blue (AB), AB-PAS, according to the M i j l l e r -M o w r y method for acid mucopolysaccharides (M c M a n u s & M o w r y 1960: 135), W i l d e r ’s reticulum stain, and G a b e ’s stain for elastic fibres. 3. Winteria telescopa B rauer. A specimen, 99 mm long (standard length), from Dana st. 3847 111 was dissected; the posterior part of the intestine, the rectum, the rectal bulb, and part of the ventral body wall including the anus were removed as a whole, embedded in paraffin, cut into 8 ,u serial sections, and stained with E h r l ic h ’s hematoxylin and eosin, H e id e n h a in ’s iron hematoxylin, H e id e n iia in ’s azocarmine-aniline blue stain. F o o t ’s modification of M a s s o n ’s trichrome stain (F o o t 1933), PAS, AB, AB-PAS, the R i n e - h a r t -A b u l -H a j stain for acid mucopolysaccharides. G r a m ’s stain for bacteria in sections (L il l ie 1954: 371), and according to B o d ia n ’s protargol method. The plane of sectioning was at right angles to the median plane of the animal and transversal to the pear-shaped rectal bulb. All specimens were fixed in formalin. *) In accordance with Cohen 1960 Monacoa W h itley is regarded as synonymous with Ophisthoproctiis V aillant. *) Cf. foot-note p. 13. ANATOMY OF LIGHT AND REFLECTOR ORGANS A. Opisthoproctus soleatus and grimaldii. The position and relative size of the light and reflector organs in an adult Opisthoproctus soleatus is shown diagrammatically in Fig. 1. As no principal differences were found between Opisthoproctus soleatus and 0. grimaldii in the structure of these organs, the following description covers both species. Fig. 1. Position of light organ and reflector in Opisthoproctus soleatus. Above: Diagram based on dissections and serial sections of adult specimen 42 mm in standard length. I-III transversal section of reflector. IV median section of rectal bulb and posterior part of reflector. Below: Ventral view of adult showing sole and position of anus (an). 1. The rectal bulb. (Figs. 2-4 and Plate 1). The highly vascularized rectal bulb of the adult specimens shows a heavy pigmentation except in the ventral region of contact with the reflector organ where the wall is unpigmented and functions as a window between the lens and the hyaloid body (w in Figs. 3, 4 and Plate I 2). The bulb is completely fdled with lon­ gitudinal folds formed by the mucous membrane of the rectum leaving only a narrow ventral passage for the faeces. The ventral part of the wall shows only a few low folds, whereas the dorsal and lateral parts pos­ sess high, narrow, tightly packed folds. Two specialized cell types are found in these folds, viz. luminous epithelium and lens cells (Fig. 4 and Plate I). The folds originating from the lowermost parts of the lateral walls only show lens cells. On the folds originating from the upper parts of the lateral walls luminous epithelium is seen in the proximal parts of h m ' Fig. 2. Rectal bulb and posterior part of reflector in Opislhoproclus solealiis. Based on dissection of adult specimen. Lettering Figs. to 2 and 3; an: anus; ar: rudimental anal fin rays; h: hyaloid body; hi; lateral part of hyaloid body; hm; median part of hyaloid body; i: intestine; 1: lens; 11: distal part of folds with low epithelial cells; lu: proximal part of folds with luminous epihelial cells; ml: dorsal striated muscle of reflector organ;.m2: posterior striated muscle of reflector organ; pc: pigmented connective tissue; pt: ptery- giophor of anal fin rays; rb: rectal bulb; s: median septum of hyaloid body; u: urogenital duct; v: blood vessel; w: window. the folds, lens cells in the distal parts. The major part of the folds originating from the dorsal wall do not carry lens cells and show luminous epithelium pro.'cimally, whereas the ridges of the folds are covered with low epithelial cells. The same tj’pe of low cells is found intercalated between the lens cells and the luminous epithelial cells on folds carrying both of these cell types. The lens cells on the tightly packed folds form to­ gether a lentiform body in the ventral part of the bulb (Fig. 3 and Plate I). The spaces between the folds of the rectal bulb contain a granular material which at high magnification is seen to consist of a great number of spheroid elements of uniform size, measuring appr. 2 // (g in p-ig. 4 and Plate I). Each element contains several darkstained granules which are generally situated peripherally. These elements might very well be bacteria in which the nuclear material has been stained by the phosphotungstic acid hematoxylin. We have not in any of the specimens examined observed secretion in the lumen between the folds of the rectal bulb. The luminous epithelium consists of cuboidal-columnar cells showing a heavy yellow colour which com­ pletely masks the nuclei; this colour was also seen in unstained longitudinal sections of the rectal bulb in adult specimens of both species. In some places blood vessels were seen in the connective tissue in the prox­ imal parts of the folds corresponding to the luminous epithelium. The lens cplls are high columnar cells with a hyaline cytoplasm. We have not been able to recognize any nuclei in the lens cells of adult specimens, but since the sections are very thick and the cyto­ plasm is often heavily stained, this does not necessarily mean that nuclei are absent. The distal part of the rectum behind the rectal bulb possesses a heavily pigmented wall. Furthermore the wall is thickened owing to the presence of abundant loose connective tissue.

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