FISHERY BULLETIN: VOL. 76, NO 3 



somewhat further separated. The ommastrephids 

 have the unusual habit of usually living in 

 epipelagic waters but occasionally descending to 

 great depths (Roper and Young 1975). Perhaps the 

 central organs function in epipelagic waters while 

 the dorsal organs operate only in deep water. Cer- 

 tainly there are considerable problems associated 

 with a single organ functioning over such a wide 

 range of light intensities. 



Certain photosensitive vesicles appear to detect 

 bioluminescent light rather than downwelling 

 skylight. The small vesicular organs in the deep- 

 living Vampyroteuthis infernalis are shielded 

 from downwelling skylight (Young 1972a). Ves- 

 icular organs are present in the blind bathypelagic 

 octopod Cirrothauma murayi (J. Z. Young in 

 Packard 1972) which lives in depths where detect- 

 able surface light is absent. Certain photosensi- 

 tive vesicles of many other species were shielded 

 from downwelling light. Such organs presumably 

 detect bioluminescent light. Young (1973, 1977) 

 demonstrated that certain vesicular organs in 

 some species were directly exposed to the animal's 

 photophores, presumably for counterillumination 

 purposes. 



The detection of bioluminescence is not limited, 

 however, to the animal's own photophores. With 

 only a few exceptions all species examined had 

 some means of "viewing" various parts of the man- 

 tle cavity with their vesicular organs. In many 

 cases, the organs seemed precisely placed for this 

 purpose (see Figure 6). In most species with large 

 opaque livers (e.g., ommastrephids, enop- 

 loteuthids, histioteuthids, bathyteuthids, cy- 

 cloteuthids, octopoteuthids, and mastigoteuthids), 

 some organs extended laterally or ventrally past 

 the liver, enabling a "view" of the mantle cavity. 

 In other species with the liver far back in the 

 mantle cavity (e.g., cranchiids, Brachioteuthis, 

 Ctenopteryx), only central organs were present. In 

 Vampyroteuthis infernalis, the organs lay within 

 the mantle cavity and could only be exposed by 

 light originating within this cavity, the funnel, or 

 at the mantle opening. This animal, like most 

 other cephalopods, had no photophores in these 

 locations. The photosensitive vesicles in octopods 

 were also located within the mantle cavity. The 

 view of the mantle cavity is obscured only in 

 Onychoteuthis, Chiroteuthis , Joubiniteuthis, and 

 Chiroteuthidae gen. sp., although most of these 

 species could still detect light from within the fun- 

 nel and at the entrance to the mantle cavity. 



Young (1972a) suggested that the photosensi- 

 tive vesicles in Vampyroteuthis detect small glow- 

 ing organisms that are carried into the mantle 

 cavity with the respiratory current. In the deep 

 sea, a glowing organism within the mantle cavity 

 could reveal the squid's location and have disas- 

 terous consequences. J. Z. Young ( 1977) extended 

 this idea to octopods. Nevertheless, this sugges- 

 tion seems unlikely to have broad application in 

 explaining the consistent relationships between 

 vesicle location and mantle cavity "visibility"; 

 however, no alternative function has been found. 



Some squid may detect bioluminescent light 

 originating outside the animal. The large vesicu- 

 lar organs in the deep-living Bathyteuthis abys- 

 sicola are not exposed to its own photophores and 

 probably detect bioluminescence from animals lo- 

 cated outside its restricted visual field (Young 

 1972a). In Ctenopteryx siculus, the elongate ves- 

 icular organs joined in the midventral line over 

 the funnel and were there shielded dorsally and 

 laterally by a thick layer of iridophores. The ven- 

 tral part of this organ would detect light originat- 

 ing within the funnel. Yet, the high organization 

 and sophisticated structure of the vesicles seem 

 overly matched for such a task. This organ proba- 

 bly "looks" ventrally through the funnel to the 

 area below the squid. Similar arguments could be 

 made for certain lobes in other squids. 



The photosensitive vesicles in many cephalo- 

 pods apparently form an elaborate system for 

 monitoring bioluminescent light from their own 

 photophores, from within the mantle cavity, and 

 from the immediate vicinity of the animal that lies 

 outside the visual field 



The great variety of photosensitive vesicles 

 found among the species of pelagic cephalopods off 

 Hawaii presumably reflects a variety of functions 

 for these organs associated with the detection of 

 both downwelling and bioluminescent light. The 

 morphology and placement of these organs have 

 provided some clues to these functions. A full un- 

 derstanding of this complex sensory system, how- 

 ever, must await experimental studies on living 

 animals. 



ACKNOWLEDGMENTS 



I wish to thank the Captain and the crew of the 

 RV Teritu and the many people that participated 

 in the "Teuthis" cruises. Of these, I especially 

 thank John Walters, Steven Amesbury, Sherwood 

 Maynard, and Fletcher Riggs. Most of the 



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