YOUNG: VERTICAL DISTRIBUTION AND PHOTOSENSITIVE VESICLES 



posteroventral surfaces. The sensory processes 

 within the vesicles are highly organized, particu- 

 larly in the ventral portions. The wall of the organ 

 is not particularly thick, and usually has two ir- 

 regular layers of sensory-cell bodies. The sensory 

 processes arise from all sides of the vesicles; they 

 are straight, parallel, and fill the lumen in the 

 ventral parts of the organ. The sensory processes 

 are about 30 to 50 ^im long and lack a detectable 

 core. The dorsal end of the organ lacks the 

 iridophore sheath and has a slightly convoluted 

 wall; the sensory processes are somewhat more 

 widely spaced and do not fill the lumen of the 

 vesicle. 



Familv Onvchoteuthidae 



IIANILC lENC'M 



20 40 60 120 



MANTLE LENGTH. mm 



Figure 18. — A. Vertical distribution of Octopoteuthis 

 nielseni. B. Vertical distribution of Cycloteuthis serventyi 

 (triangles) and Discoteuthis laciniosa (circles). Symbols as in 

 Figure 1. 



Onychotenthis com pacta (Berry 1913) 

 Vertical Distribution (Figure l6B) 



Twenty-five specimens were captured. Eleven 

 specimens taken during the day came from depths 

 of 240 to 1,350 m. At night, 12 of 14 captures were 

 made between the surface (dip net) and 115 m. The 

 two remaining captures came from depths of 190 

 and 310 m. 



Photosensitive Vesicles (Figure 17B) 



Onychotenthis compacta has a single set of or- 

 gans. Each organ consists of a large number of 

 small, tightly packed vesicles. Each organ is lo- 

 cated on the posterior edge of the optic stalk and 

 extends ventrally and slightly laterally below the 

 central brain along the medial side of the optic 

 lobe. The ventrolateral portion of the vesicle lies 

 directly posterior to the side of the liver and just 

 medial to the head retractor muscles and im- 

 mediately above the funnel. 



Family Octopoteuthidae 



Octopoteuthis nielseni Robson 1948 



Vertical Distribution (Figure 18A) 



Three specimens captured during the day came 

 from depths of about 650 to 765 m. The six night 

 captures came from depths between 100 and 200 

 m. 



Photosensitive Vesicles (Figure 19A) 



Two sets of organs are present. A compact ven- 

 tral organ lies embedded in the thick cephalic car- 

 tilage at the anterolateral edge of the statocyst 

 and just medial to the insertion of the head retrac- 

 tor muscles. This organ consists of large, globular, 

 independent vesicles tightly packed together. A 

 series of narrow, very elongate vesicles lie along 

 the nerves from the organ. The central organ lies 

 on the posterior surface of the optic stalk adjacent 

 to the peduncle complex. This large and rather 

 irregularly shaped organ consists of numerous 

 small vesicles. 



DPV 



Figure 19. — A. Photosensitive vesicles of Octopoteuthis 

 nielseni. Photosensitive vesicles of Cycloteuthis serventyi. Ab- 

 breviations as in Figure 2. 



595 



