Chiroteuthis Bioluminescence

Richard E. Young and Clyde F. E. Roper

While species of Chiroteuthis have a variety of luminous organs, few observations exist that suggest how these organs function or that they are indeed photophores. We summarize here a few of our brief observations.

A damaged Chiroteuthis sp. B held for a short time in a shipboard aquarium would flash photophores brilliantly when grabbed by the fins. As many as 7-8 individual organs at a time would flash for about 1-5 seconds duration. The distal half of the tentacle was missing and flashes seemed to come from the remaining portion of the tentacle on some occasions and from the ventral arms on other occasions.

A Chiroteuthis picteti (82 mm ML) held in a shipboard aquarium for about three hours produced luminescent displays that were quite different from that described above.The ocular photophores were observed to glow brightly and steadily for several minutes at a time (perhaps as long as 5 min.). At one point the tentacles became completely illuminated (no discrete photophores were visible) for several minutes. Several bright flashes were seen away from the eyes but the source (presumably ventral arms or tentacles) could not be determined. On one occasion a faint but distinct diffuse luminous cloud was produced that included luminescent particles. The cloud and most particles disappeared in approximately 20 seconds although the last particle to disappear took about 45 seconds. After handling the squid in the tank luminescent material was observed adhering the observor's skin. Unfortunately the source of the secreted luminescence in unknown but it presumably was discharged either from the tentacle photophores or the mantle cavity.

Hunt (1996) observed bioluminescent displays of the tentacle photophores of Chiroteuthis calyx in a laboratory aquarium. "When disturbed Chiroteuthis thrust its tentacles forward, lit the tentacle photophores, and used the fourth arms to spread the tentacles laterally." A quick side movement of one of the fourth arms would be translated down the tentacle as a wave, progressively moving the tentacle to the side. "The result was that the tentacles appear to be joined [at the head] into one long strand. Photophores luminesced along the entire length at regularly spaced intervals."

The ability of the tentacle-stalk photophores to open and expand like a flower or contract and close over combined with the peculiar distribution of reflective tissue on the tentacle stalk and especially the club suggest that species of Chiroteuthis have unusual luminescent displays that may never be fully understood or appreciated until observed in the squid's habitat in the mid-depths of the ocean.

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University of Hawaii, Honolulu, HI, USA

Smithsonian Institution, Washington, D. C., USA

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