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Taningia danae, a deep-sea bioluminescent squid<< Cephalopod Species
On exhibit in the National Museum of Natural History (Smithsonian Institution) in Washington (where Roper is Curator of Invertebrate Biology), is a specimen of the squid known as Taningia danae, seven feet long and weighing 135 pounds. Unlike most other squids, Taningia does not have two long feeding tentacles, but it does have something more surprising: on the ends of two of its arms are gigantic yellow photophores, the largest light-producing organs in any known animal. These lemon-colored (and lemon-sized) photophores can be flashed at will, because they are equipped with a black, eyelid-like membrane that can be opened or closed. In addition, this species has claws—likened to those of a cat—on the suckers of its arms. The Smithsonian's specimen was dumped into the hold of the Georges Bank fishing boat Defender as Captain George Dow emptied his nets. He was 200 miles southeast of Portland, Maine, when his engineer came up to the bridge and asked, "Ever seen a seven-foot squid?"
The specimen was alive when it was captured, and Dow iced it down and delivered it to the National Marine Fisheries Service (NMFS) laboratory in Gloucester, Mass., where it was photographed and a videotape made of it as it swam around an aquarium. (Surprisingly, this was the first record of Taningia from the western North Atlantic, one of the most heavily fished areas in the world, and one in which biological sampling has been going on for well over a century.)
Taningia was named by Joubin in 1931 from a specimen caught off the Cape Verde Islands during the oceanographic cruises of the Danish research vessel Dana, hence its specific name danae. The generic name is from AageVedel Tåning (1890-1958), an eminent Danish fisheries biologist who also had several species of fishes named for him, as well as the lantern fish genus Taaningichthys. The nomenclatural history of this widespread species is so complicated that the early records are quite confused. At various times, this species was known as Cucioteuthis unguiculatus and Enoploteuthis cooki, and since many of the early specimens have been lost, it is often unclear as to which species was actually being referred to. (Cucioteuthis comes from the Greek for coconut; unguiculata is derived from unguis, which is Greek for "talon." Enoplos is Greek for "armed", as with weapons, and cooki is an honorific for Captain Cook.)
Not much is known of the biology of Taningia, but sperm whales must have some of the answers, since most known specimens have been taken from the stomachs of captured whales. (According to a 1993 review by Roper and Vecchione, other specimens have come from the stomachs of sharks, lancetfishes, tunas, wandering albatrosses and elephant seals.) In 1959, the stomach contents of a whale were examined by Malcolm Clarke at the Canaçal whaling station on the island of Madeira. There were 4,000 beaks, 28 partially digested squids, and "a perfectly intact specimen" of the squid then known as Cucioteuthis unguiculata, but now called Taningiadanae. ("Other specimens," wrote Clarke, [that] "were referred to Cucioteuthis unguiculata should all be regarded as Taningiadanae.") Clarke (1962a) wrote that it was "easily recognized by the large, gelatinous body, the broad fins extending almost to the front of the mantle, the absence of long tentacles (there being only eight arms); and the presence of strong hooks on the arms." The mantle was measured at 140 cm (4.55 feet).
From the records collected by Roper and Vecchione, it appears that Taningia has an almost worldwide distribution, having been collected—largely from the stomachs of sperm whales—in the western North Atlantic, off Bermuda, Hawaii, South Georgia, South Africa, Japan, Australia, New Zealand, the Azores—in short, almost everywhere that sperm whales were hunted.(*1) They wrote, "with the addition of the material in this paper, the geographical distribution of Taningia danae can be described as truly cosmopolitan with the exception of the polar regions. It occurs in all major ocean basins, in central waters, near oceanic islands, near continental slopes. It occurs in warm, temperate, and sub-boreal waters." A species that is found all over the world, and in such a variety of habitats, is a rarity among cephalopods.
Now that hunting of sperm whales has ceased, the modern records must depend on net hauls, which are more useful for determining geographical distribution and other aspects of the biology of Taningia, but less useful for collecting the larger specimens. "Our material," wrote Roper and Vecchione, "expands the knowledge of this species through a number of specimens collected in a variety of nets, not predators."
A small specimen (23.4 inches ML), captured at night off Hawaii was alive and undamaged and placed in a shipboard aquarium, where it was observed and photographed. Although Joubin's 1931 description of the species suggested that the organs at the tips of the arms were photophores, their luminescence had never been directly observed. Aboard the ship, Clyde Roper put the specimen in complete darkness, and the observers' eyes were allowed to adapt thoroughly to the dark. Without the aid of a light one observer slowly moved his hand around in the aquarium in an effort to stimulate a response. This is what happened:
Two primary responses were evoked. Both included bright flashes of brilliant blue-green light simultaneously from both arm-tip photophores. The most common reaction involved the coordinate flashes accompanied by an attack, grasping the researcher's fingers and biting. The second reaction... involved a bright flash followed by a rapid retreat from the stimulus. The flashes appeared to vary somewhat in intensity and duration. Usually the flashes lasted only a fraction of a second, but occasionally the organs glowed with fluctuating intensity for 1-7 seconds. These prolonged glows were associated with continuous stimulation, such as pinching of the fins. During these prolonged glows the intensity of the light appeared to increase gradually to a peak and then it receded gradually.
Very interesting for Roper and Young, but what did these responses suggest about the natural behavior of Taningia? The bright, quick arm-tip flashes startled the observers, and created the impression that the flashes serve to startle, distract, and confuse an approaching predator. How effective this is on smaller predators can only be imagined at this time. Clearly large predators are not always foiled, because they are by far the largest source of specimens of T. danae in collections. The predators include visual hunters such as tunas and lancetfishes. Perhaps because sperm whales hunt using sonar rather than vision, flashing by T. danae is a particularly ineffective defense against these predators.
Even though they do nothing to deter a 60-foot long sperm whale, the stroboscopic flashes of Taningia must be among the most terrifying sights in the blackness of the abyss—if the prey manages to survive the shock of a seven-foot-long carnivorous squid with stroboscopic arm flashers.
Taningia danae is included in the family of eight-armed squid (Octopoteuthidae) because while the juveniles have two tentacles in addition to the eight arms, by the time they mature, the tentacles are reduced to rudimentary filaments or disappear altogether. They are worldwide in distribution, and are believed to live at depths down to 3,000 feet. In his 1967 discussion of this species, Malcolm Clarke wrote that "in the smallest individual, chromatophores are dotted over the surface, while the larger specimens have an evenly colored magenta skin." The specimen on exhibit in the Smithsonian extends the range to the Gulf of Maine and therefore, to both sides of the North Atlantic. In tabulating the squid species eaten by sperm whales off Japan, Okutani and Satake (1978) identified two specimens of Taningia danae from whales taken north of Honshu Island. Unlike some of the Atlantic specimens, these two were small, measuring 35.5 cm (13.8 inches) and 47.5 cm (18.5 inches) in dorsal mantle length.(*2)
Notes*1 In 1980, three specimens, one "in almost perfect condition," were found floating offshore in South Australian waters. When Wolfgang Zeidler of the South Australian Museum described them, he wrote, "Nearly all known specimens of Taningia have been collected form sperm whale stomachs, and it is unusual to encounter them floating at the surface. It is possible that they were regurgitated by sperm whales, and this may be the case for the specimen lacking a head, but the other two were in relatively good condition, and the fishermen estimated that they had died only recently."
*2 When Roper and Vecchione (1993) examined several specimens of Taningia that had been caught off Hawaii, they identified an additional pair of photophores "on each side of the intestine, ventral to the ink sac." North Atlantic specimens examined by Herring, Dilly, and Cope (1992) exhibited no additional photophores, raising the question that there might be more than one species in the genus.
References and CreditsText and illustration are from the "Battle of the Giants" chapter in "The Search for the Giant Squid" by Richard Ellis. "The Search for the Giant Squid" will be published by Lyons Press in New York, in October 1998. Thanks Richard!
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