YOUNG: VERTICAL DISTRIBUTION AND PHOTOSENSITIVE VESICLES 



Photosensitive Vesicles (Figure 6) 



The arrangement of organs is similar to Ab- 

 raliopsis sp. described by Young ( 1973). Four sets 

 of organs are present; all lie adjacent to the 

 cephalic cartilage. One set is located dorsally, one 

 posteriorly, and two ventrally. Each dorsal organ 

 is situated in a concavity of the cephalic cartilage 

 at the posterodorsal edge of the head. The organ is 

 compact, dorsoventrally flattened and circular to 

 triangular in outline. The posterior organs are 

 located on the posterior surfaces of the optic lobes. 

 Each is approximately elliptical and very flat. The 

 posterior organs have a strong yellow pigment 

 which does not fade after fixation. Other organs 

 contain an orange pigment that is lost after fixa- 

 tion. The posterior organs lie immediately an- 

 terior and lateral to the opaque liver and directly 

 anterior to the attachment zone of the transparent 

 head retractor muscles (Figure 6B). The ventral 

 organs on each side consist of two, narrowly joined, 

 flattened lobes. One of these, the anteroventral 

 lobe, is located somewhat anterior and medial to 

 the other. The anteroventral lobe has its medial 

 and anterior ends in a deep depression of the 

 cephalic cartilage. The anteromedial edge of each 

 lobe nearly makes contact with its counterpart of 



p PV 



Figure 6. — A. Photosensitive vesicles oiAbralia trigonura . B. 

 Ventral view of A. trigonura with portion of mantle removed. 

 This illustration shows the relationship between the posterior 

 photosensitive vesicles, the opaque liver (L), and the mantle 

 cavity. Abbreviations as in Figure 2. 



the opposite side. The more posterior of the two 

 lobes, the midventral lobe, lies between the ven- 

 tral surface of the optic lobe and the cephalic carti- 

 lage. 



Circular windows, similar to those described in 

 Abraliopsis sp. (Young 1973), and characterized 

 by a reduced number of chromatophores, are pres- 

 ent above each dorsal organ. A large ventral win- 

 dow, totally lacking chromatophores, lies on the 

 ventral surface of the head above the funnel and 

 below the ventral vesicles. 



Ahralia astrosticta Berry 1909 



Vertical Distribution 



No specimens were captured during the present 

 program. However, one specimen was taken in a 

 gill net set overnight by T. Clarke on the bottom in 

 180 m. The National Marine Fisheries Service, 

 NOAA, has captured 44 juveniles (7-38 mm ML 

 (Mantle length)) in pelagic trawls between 10 and 

 130 m at night and 10 adults in a benthic shrimp 

 trawl at 110 m at night near Hawaii. The type was 

 captured in a bottom dredge between 354 and 650 

 m, presumably during the day. Roper and Young 

 (1975) indicated that this animal lives near the 

 ocean floor even when migrating. 



Photosensitive Vesicles 



The organs and associated windows are basi- 

 cally the same as in A. trigonura. 



Abraliopsis sp. A 



Vertical Distribution (Figure 7) 



Sixty-seven specimens were captured. Exclud- 



O 600 - 



800 - 



22 26 30 34 



MAN TIE LENGTH, mm 



Figure 7. — Vertical distribution of Abraliopsis sp. A. Symbols 

 as in Figure 1. 



589 



