[4] They have very large forward-facing eyes, each possessing three bioluminescent organs (photophores), a defining characteristic of the genus Teuthowenia.

They extend past the rear tip of the body, fuse with each other at the middle, and end with a pair of small lobes.

The mid-arm and basal suckers of the third and fourth pairs also have swollen collars and greatly reduced openings.

They have four rows of carpal ("wrist") suckers, arranged into a zigzag pattern on ½ to ⅔ of the distal end of the tentacles leading towards the tentacular clubs.

The suckers on the tentacular club are set on long protrusions and possess numerous short, sharp teeth on their entire margins.

They exhibit diel vertical migration, moving closer to the surface in nighttime and diving deeper during daytime.

Paralarvae and subadults are usually found in the upper 300 m (980 ft) of the surface, and gradually dive deeper as they grow larger.

In the northwestern Atlantic, they can be found along the eastern coast of North America, from Labrador in Canada to Georgia in the United States; extending eastward towards the Bermuda islands and the New England Seamounts.

[2][14] In the northeastern Atlantic, they inhabit the waters between Greenland and Iceland and south towards the Azores (following the Mid-Atlantic Ridge);[15][16] and the area around the Rockall Basin, Britain, Ireland,[17][18][19] and (during winter) northern Portugal.

[26] Like other members of the family Cranchiidae, Teuthowenia megalops possess a remarkable flotation system that enables them to remain in the water column at neutral buoyancy.

The system uses enormous bilobed coelomic chambers filled with ammonium chloride derived as waste products from their nitrogen metabolism.

Unlike other squids, they do not need to contract their mantle muscles to breathe, but their modified flotation and respiratory systems restrict their ability to jet away from threats.

In this posture, they rotate around their spindle-shaped digestive glands, the only internal organs of the squid clearly visible through their mostly transparent bodies.

[21] Teuthowenia megalops are preyed upon by predatory fish like the blue shark (Prionace glauca) and swordfish (Xiphias gladius).

At this point the chromatophores (normally mere pinpoints in its predominantly transparent body) expand to about four times their usual diameter.

[34] The squid retains the shape for about half an hour then its starts to tentatively extend its head and tentacles out of the mantle, followed by the fins and gladius.

[37] In 1850, the Danish malacologist Otto Andreas Lowson Mörch pointed out mistakes in Prosch's original description.

[36] In 1856, the Danish zoologist Japetus Steenstrup mentioned a specimen of cranchiid squid recovered from Baffin Bay which he had named Leachia hyperborea.

In the same work, he was also the first to point out that Prosch had made the error of including juveniles of Gonatus along with his diagnosis of Cranchia megalops.

Though the type specimens were destroyed in World War II, examinations of his description and illustrations reveal that Megalocranchia maxima was definitely not from the genus Teuthowenia.

Thus in 1910, the German zoologist Carl Chun established the genus Teuthowenia in its place, from Greek τευθίς (teuthis, "squid") + Owen, as in the original name.

[46] In 1912, the American zoologist Samuel Stillman Berry agreed with Hoyle in concluding that Verrill's Desmoteuthis is a synonym of Taonius.

The second was that he did not realize that the distinctive end-organs on his specimen for Desmoteuthis thori was actually a characteristic of Teuthowenia megalops found only in maturing and adult females.

[49] It was only in 1956 when the Danish marine biologist Bent J. Muus discovered that Prosch's Cranchia (Owenia) megalops and Steenstrup's Leachia hyperborea actually belong to the same species.

Like Chun, he also made the mistake of including several other unrelated specimens in the species, including Anne L. Massy's Helicocranchia pfefferi, and Chun's Desmoteuthis pellucida and Teuthowenia antarctica (now known to be Galiteuthis glacialis); thus coming to the mistaken conclusion that Teuthowenia megalops inhabits both the northern and southern hemispheres.

[50][51] In 1960, the American teuthologist Gilbert L. Voss disagreed with Muus' choice of Desmoteuthis, but also mistakenly followed Berry and thus used the genus Megalocranchia instead.

[9] In 1962, the Belgian malacologist William Adam disagreed with both Voss and Muus, and used Berry's Verilliteuthis for a specimen recovered off the coast of Angola (now identified to be Teuthowenia maculata).

Clarke's new combination was the primary name used by subsequent authors until 1985 when the American malacologist Nancy A. Voss finally clarified the convoluted taxonomic history of the family Cranchiidae, retaining Chun's Teuthowenia.

[4] A photo of a balled-up Teuthowenia megalops was taken by David Shale in 2006 while on a MAR-ECO expedition led by Monty Priede, Director of Oceanlab of the University of Aberdeen.

[53][54] The photo was also posted to the blog Cute Overload, where its comical appearance earned it the nickname Eddie McBlobbles, "the inside-out-seahorse-in-a-ball-nerd of the deep.