YOUNG: VERTICAL DISTRIBUTION AND PHOTOSENSITIVE VESICLES 



^^ - — - D PV Photosensitive Vesicles (Figure I OB) 



Three sets of organs, dorsal, posterior, and ven- 

 tral, consist primarily of a loose association of var- 

 iously shaped, mostly independent vesicles 

 (Young 1977). The organs are broad, flat struc- 

 tures, with the greatest concentration of vesicles 

 along the lateral margins of the organs. The or- 

 gans lack yellow pigment. 



Family Ommastrephidae 



Symplectotenthis oualaniensis 

 (Lesson 1830) 



PPV 



Figure lO.— A. Photosensitive vesicles oi Enoploteuthis sp. 

 A. B. Photosensitive vesicles of Thelidioteuthis alessandrinii . 

 Abbreviations as in Figure 2. 



with the following exceptions. The midventral 

 organ has a more irregular shape, is less compact, 

 and has a narrow connection with the posterior 

 organ. The posterior organ is continuous with the 

 dorsal organ via a strand of vesicles that extends 

 over the optic lobe. Except for a short segment 

 adjacent to the dorsal organ, this strand contains 

 yellow pigment as does the posterior lobe. 



Enoploteuthis sp. B 



Vertical Distribution (Figure 9B) 



One specimen was captured during the day at 

 515 m and three were taken at night between 50 

 and 150 m. 



Photosensitive Vesicles 



The vesicles are the same as those of Enop- 

 loteuthis sp. A except for some differences in the 

 posterior organ. The posterior organ in Enop- 

 loteuthis sp. B is more elongate, more medially 

 located on the optic lobe, and lacks yellow pig- 

 ment. 



Thelidioteuthis alesandrinii (Verany 1851) 



Vertical Distribution (Figure 9A) 



During the day, one specimen was taken in an 

 opening-closing tow between 720 and 780 m. At 

 night, three specimens were taken in open tows 

 between 80 and 100 m. 



Vertical Distribution 



Except for larvae, only one specimen was cap- 

 tured in the midwater trawls. This specimen was 

 taken at night by the IKMT which fished at 100 m. 

 This fast-swimming squid normally avoids our 

 trawls. Members of this species are commonly 

 seen at the surface at night around the night-light 

 and a number have been dipnetted. Little is 

 known, however, of their day distribution, al- 

 though Young (1975b) had assembled evidence 

 which indicates that they live in the upper few 

 hundred meters but may descend on occasion to 

 great depths. 



Photosensitive Vesicles (Figure IIA) 



Three sets of organs are present: a dorsal, cen- 

 tral, and ventral set. The ventral organ lies within 

 the cephalic cartilage at the posterior end of the 

 head and immediately above the posterolateral 

 portion of the funnel. It consists of a series of flat, 



D PV 



Figure ll. — A. Photosensitive vesicles of Symplecoteuthis 

 oualaniensis. B. Photosensitive vesicles of //ya/o<eu</iJspe/ag- 

 icus. Abbreviations as in Figure 2. 



591 



