YOUNG: VERTICAL DISTRIBUTION AND PHOTOSENSITIVE VESICLES 



However, in the tropical North Atlantic, two 

 specimens of L. reinhardti (44 and 48 mm ML) 

 were captured during the day in opening-closing 

 tows between 510 and 600 m, while a 75-mm ML 

 specimen was taken in an open tow that fished 

 between 390 and 800 m (C.C. Lu pers. commun.). 

 Also, M. Clarke ( 1969) reported specimens of 46 

 and 69 mm ML from depths between 450 and 810 

 m during the day in the Atlantic. 



Photosensitive Vesicles (Figure 30B) 



The organs of L. reinhardti have been described 

 by Messenger (1967a). This species has a single 

 large set of organs lying along the posteromedial 

 surface of the peduncle lobe. Each organ consists of 

 a linear array of 20 to 25 tightly packed vesicles. 

 The vesicles are elongated in a transverse direc- 

 tion except for those at the dorsal and ventral ends 

 which are nearly circular. The vesicles are sepa- 

 rated from one another by a heavy brown pigment 

 screen which also covers most of the convex an- 

 terior side of the organ. Most vesicles within each 

 organ thus form elongate cups which presumably 

 admit light only from one surface. The dorsal vesi- 

 cle, however, lacks screening pigment from the 

 posterior lateral and dorsolateral surfaces. The 

 ventral vesicle is larger, with photosensitive pro- 

 cesses twice as long as those of the dorsal vesicle. It 

 lacks pigment on its ventral and anterior surface. 

 The curvature of the organ and the arrangement 

 of screening pigment allows light to enter dif- 

 ferent vesicles from a wide range of angles. 



Specimens ^47 mm ML have no screening pig- 

 ment on the vesicles while those 2*70 mm ML 

 exhibit pigment as described above. The vesicles 

 in the largest specimen (spent female) are slightly 

 larger (especially the ventral vesicle) relative to 

 the brain size than in smaller specimens. 



Leachia pacifica (Issel 1908) 



Vertical Distribution (Figure 32) 



The vertical distribution of L. pacifica has been 

 described elsewhere (Young 1975a). This species 

 reaches about 809^ of its maximum length in 

 near-surface waters. Large specimens (45-60 mm 

 ML) are found throughout the water column be- 

 tween 30 and at least 1,800 m with those taken 

 from progressively deeper water exhibiting pro- 

 gressively greater sexual maturity. Gravid 

 females were taken at depths > 1,300 m. 



200 



400- 



600 



800 



)000 



6 )200 



I 

 t— 



a. 



Q )400 



16001- 



1800 

 2000 

 22001- 

 2400, 



10 20 30 40 50 60 



MANTLE LENGTH, mm 



Figure 32.— Vertical distribution of Leachia pacifica. From 

 Young ( 1975a). Symbols as in Figure 1. 



Photosensitive Vesicles (Figure 33A) 



Leachia pacifica has a single set of organs lo- 

 cated on the posteroventral surface of the peduncle 

 lobe. Each organ consists of 4 or 5 cup-shaped 

 vesicles that are closely packed into a small oval 

 organ. A dark brown screening pigment covers 



Figure 33. — A. Photosensitive vesicles of Leachia pacifica . B. 

 Photosensitive vesicles of Sandalops melancholicus. Abbrevia- 

 tions as in Figure 2. 



601 



