FISHERY BULLETIN: VOL. 76. NO. 3 



narrow vertical ranges day and night until sexual 

 maturity was reached; a poorly defined ontogene- 

 tic descent then ensued. Unfortunately, no other 

 clues to spawning depth are known. 



The nonmigrating species that exhibit a 

 gradual ontogenetic descent would be expected to 

 spawn at the lower end of their range. Indeed, this 

 appeared to happen in Bathothauma lyromma. 

 The most dramatic example occurred in Leach i a 

 pacified. Young (1975a) demonstrated that this 

 species descends near the time of sexual maturity 

 from near-surface waters to depths of 1,000 to 

 2,000 m to mate and spawn. 



Larvae of most pelagic oceanic cephalopods 

 occur in near-surface waters. Upward migration of 

 larvae would seem to be a formidable task for 

 species that spawn at great depths. The deep- 

 living octopods apparently carry their young 

 partway up presumably to lighten this task. 

 Perhaps squid egg masses are positively buoyant 

 and float to the surface. There are a number of 

 observations of egg masses of pelagic cephalopods 

 floating at or near the ocean surface (see Clarke 

 1966). However, these have yet to be shown to 

 belong to a deep-spawning species. 



Photosensitive Vesicles 



These vesicular organs were present in all 

 Hawaiian pelagic cephalopods and they occurred 

 in a great variety of shapes, sizes, and locations. In 

 many squids, the organs were subdivided into as 

 many as four sets of separate organs. In squid, the 

 organs were always found within the confines of 

 the cephalic cartilage and were located either on 

 the optic stalk ( central organs ) or dorsal, posterior, 

 or ventral to the optic stalk (dorsal, posterior, and 

 ventral organs, respectively). The separate organs 

 often faced different directions (i.e., their broadest 

 surface faced a dorsal, posterior, or ventral direc- 

 tion). 



These separate organs were frequently as- 

 sociated with distinctive "windows" in the overly- 

 ing skin bearing few if any chromatophores. Such 

 windows seem to be unnecessary since most 

 cephalopods can become quite transparent by con- 

 traction of their chromatophores. The windows in 

 combination with the more pigmented surround- 

 ing skin, however, may restrict light to specific 

 receptors and thereby improve the directionality 

 of the organs. In a few cases (e.g., Phasmatopsis 

 fisheri and Ctenopteryx siculus ), the organ was not 

 subdivided but elongate and curved, allowing dif- 



612 



ferent portions of a single organ to face various 

 directions. A directional response of each portion 

 was insured either by heavy pigment (e.g., P. 

 fiaheri) or silvery iridophores (C siculus) which 

 shielded one surface of the organ. Not all species, 

 however, had vesicular organs that could dis- 

 criminate between dorsal, posterior, and ventral 

 sources of light. Some species had undivided cen- 

 tral organs (e.g., Sandalops melancholicus, 

 Taonius pavcj ) without apparent screening devices 

 which therefore are nondirectional. In others, the 

 total area surveyed by a nondirectional organ was 

 restricted by its cryptic position (e.g., Vam- 

 pyroteuthis). Clearly not all cephalopods use these 

 organs in the same way. 



General trends between organ size and habitat 

 depth during the day occurred in these animals. 

 Teuthoids and sepioids found in the upper 400 m 

 (neritic species and young Heteroteuthis 

 hawaiiensis) generally had small organs. Species 

 found primarily between 400 and 700 m generally 

 had large, complex organs. These included most 

 enoploteuthids, histioteuthids, probably Dis- 

 coteuthis laciniosa, Liocranchia reinhardti, and 

 young Taonius povo. Between 700 and 800 m, 

 species with large, complex organs (i.e., Cteno- 

 pteryx siculus, Phasmatopsis fisheri, The- 

 lidioteuthis allessendrinii, Cycloteuthis serven- 

 tyi, probably large Octopoteuthis nielseni, adult 

 Taonius pavo, and Galiteuthis pacificus, and 

 Bathyteuthis abyssicola) cooccurred with species 

 which had small organs (i.e., chiroteuthids, Mas- 

 tigoteuthis, Grimalditeuthis bomplandii, large 

 Liocranchia valdiuiae, and probably Neoteuthis 

 sp.). Many of the small-vesicle species had ranges 

 that extended well below 800 m, where they were 

 joined by other small-organ species (i.e., Vam- 

 pyroteuthis infernalis and probably Joubiniteuthis 

 portieri). 



The relationship of organ size to habitat depth 

 was especially marked in young Phasmatopsis 

 fisheri. The epipelagic larvae of P. fisheri, which 

 may grow to 40 and 50 mm ML had small central 

 vesicles. Upon metamorphosis and descent to the 

 adult day habitat (650-775 m), the organs became 

 greatly enlarged (Figure 34). As growth con- 

 tinued, however, a gradual positive allometric 

 growth of the organs occurred without a clear in- 

 crease in habitat depth. 



A number of species did not follow these general 

 trends. Several cranchiids exhibited gradual on- 

 togenetic descent; one of these {Helicocranchia 

 beebei) had small organs, while the others {San- 



