The pallid sailfin (Bathyembryx istiophasma) was a cryptid deep sea fish seen twice, off Bermuda in the Atlantic Ocean, during a bathysphere dive by William Beebe on 11 August 1934. Beebe classified it as an aberrant genus of flabby whalefish (family Cetomimidae).
According to Beebe, who could not make out all anatomical details during the sightings, the pallid sailfin was rather large for a deep sea fish, at least 2 ft (0.6 m) in length, somewhat elongated in shape, tapering slowly towards the tail. The tail itself was almost absent, "reduced to a tiny knob or button," but had comparatively large, vertical, sail-like fins above and below, "lengthening rapidly in a concave curve high above and far below the body ... posteriorly they were truncated...". Its mouth was wide, and it possessed long pectoral fins, "apparently rather soft, if not filamentous, broad, and abruptly rounded at the tips." Its colour was described as "sickly," "an unpleasant pale, olive drab, the hue of water-soaked flesh, an unhealthy buff," and it showed no bioluminescence whatsoever. The fish did not seem to notice either the bathysphere or its electric light.
From 1930 to 1934, Beebe and his colleague Otis Barton (1899 – 1992), based on Nonsuch Island in Bermuda, performed several pioneering deep sea dives in a bathysphere, an unpowered submersible designed by Barton. These record-setting dives allowed them to observe deep sea life alive for the first time. During a descent on 11 August 1934, at a depth of 1,500 ft (457 m), Beebe observed his first pallid sailfin after turning on an electric light at the starboard window. Beebe was in constant telephone communication with his colleague Gloria Hollister (1900 – 1988) during the dives, and described the pallid sailfin to her as he watched it.
Beebe later described what he had memorised in more detail in his formal description of Bathyembryx istiophasma and in his book Half Mile Down (1934), both written in the same year as the sighting.
Further down on the same dive, while suspended for some time at a depth of 2,500 ft (762 m), Beebe again saw what he believed to be a pallid sailfin, making this the only one of his abyssal fishes to be seen on multiple occasions. His verbal report to Hollister stated "flesh-colored one back again but can't see outline."
In his formal description of Bathyembryx istiophasma, Beebe argued that it likely belonged in or near the family Cetomimidae, the flabby whalefishes, "although it is a very distinct form." The flabby whalefishes, which exhibit extreme sexual dimorphism, are some of the deepest-living fish known. During the observation itself, he had described the fish's tailfins as "melanostomiatic," dragonfish-esque.
Five deep-sea fishes were described by Beebe on the basis of his bathysphere observations: the pallid sailfin, giant dragonfish (Bathysphaera intacta), three-starred anglerfish (Bathyceratias trilynchus), and five-lined constellationfish (Bathysidus pentagrammus), alongside the scientifically-undescribed abyssal rainbow gar. Beebe was wary of describing new species without extensive study of the animal's anatomy and behaviour, but, knowing there would be no second chances to describe the fishes he saw during his dives, he chose to assign taxonomic names to some of the most memorable and distinctive of them, with verification from Barton. The "type specimens" of these abyssal fishes were drawings made by Else Bostelmann under Beebe's supervision, showing only characteristics of which he was certain. Due to the circumstances of the observations, the lack of physical holotypes, and the absence of any later sightings, Beebe has been accused of misinterpreting or inventing his abyssal fishes, although Bathyembryx istiophasma continues to appear on taxonomic lists.
Notes and references
- Beebe, William "Three New Deep-Sea Fish Seen From the Bathysphere," Bulletin of the New York Zoological Society, Vol. 37, No. 6 (1934)
- Eberhart, George M. (2002) Mysterious Creatures: A Guide to Cryptozoology, ABC-CLIO, Inc., ISBN 1576072835
- Shuker, Karl P. N. "A Supplement to Dr Bernard Heuvelmans' Checklist of Cryptozoological Animals," Fortean Studies, Vol. 5 (1998)
- Beebe, William (1934) Half Mile Down – Online
- Gould, Carol Grant (2012) The Remarkable Life of William Beebe: Explorer and Naturalist
- Ballard, Robert D. & Hively, Will (2017) The Eternal Darkness: A Personal History of Deep-Sea Exploration