Fantastic Metropolis

How does this relate to mayfly squid range expansion? In 1949, a mating pair of walking catfish (Clarias batrachus) escaped from a Broward County fish farm. The fish quickly spread throughout South Florida. After periods of heavy rain, the catfish lives up to its name by “using its pectoral fins as crutches, wriggling its tail like a propeller” to move from pond to pond. (20) In 1956, Raymond Trainer, a professor of ecology at the University of Miami, noticed that many of the walking catfish he tagged after thunderstorms had masses of insect larvae clinging to their sides. Further investigation revealed that these “insect larvae” were actually mayfly squid juveniles. (21) In a remarkable instance of instinctive adaptation to a new environment, the female mayfly squid had recognized a variation on an old theme and proceeded to take advantage of the situation. As an unexpected consequence, the walking catfish has provided the mayfly squid with another way to populate squidless areas of the state.^[14]

Distinctive Physical Attributes

In General

Like most squid-from such shallow water species as Sepia loligo (the Swedish barking squid) to such deep water varieties as the ominous-sounding Vampyroteuthis infernalis (the vampire squid)—the mayfly squid has eight arms and two tentacles. The tentacles are longer than the arms and covered in a series of hooks designed to help bring prey to its mouth. The body consists of a mantle and a head. The mouth hides the beak, which is usually small in relation to the body and the hardest part of the squid. Its gills extract oxygen from water. Two hearts pump more blood into its brain each day than a human brain receives in a week. The squid moves using a propulsion system centered around the ejection of water from its funnel, a short, hose-like organ located on the mantle. Often referred to as a “super mollusk,” squid fall into the following classifications: Animalia (Kingdom), Mollusca (Phylum), Cephalopoda (Class), Coleoidea (Subclass), Decabrachia (Super order), Teuthida (Order), and Myopsina and Oegopsina (Sub-orders), with the mayfly squid categorized under the family Loliginidae and the genus Fons.

The average adult mayfly squid weighs about 18 ounces and, including tentacles, is about two inches long. There are no obvious differences between the male and female mayfly squid, but the female may be slightly larger than the male. That the gills process freshwater rather than saltwater is unusual but not unprecedented in the cephalopod world.

The Eyes

The rarest feature of the mayfly squid is its eyes. Like the Brazilian freshwater squid and only two other species, the mayfly squid has three eyes, the third eye hidden on the underside of the mantle. The two eyes on either side of its head are non-binocular-and therefore superior to human eyes, although they probably do not see color-but small and not as receptive to light as those of most other squid species. Given the mayfly squid’s probable origin in the Amazon, a river almost as silty as the Ganges, this is not surprising.

However, certain photophore arrangements and retina alterations of the third eye do startle even the seasoned researcher, for these arrangements and alterations suggest that the third eye produces a beam of light that aids the squid in seeing through water that has a high silt content. (23) Of even greater interest is the strange mass of nerves connected to the third eye that reminds some researchers of similar nodules found in the Amazon river dolphin (Inia geoffrensis). This almost blind cetacean navigates through the muddy river by eco-location alone. Does the mayfly squid also use a form of eco-location? No studies on this subject have as yet been completed, in part because the quick response time of squid to stimuli makes it difficult to establish controls for such experiments. (21)

Color Fluctuations

Depending on conditions such as temperature and background, the mayfly squid will manifest itself in a dull silver or in a shimmer of faint green. When startled, mating, or stalking prey, the squid displays a wide spectrum of colors and patterns across its skin. As William Blake once wrote of another type of squid entirely, the skin “flames and gutters with its own potency.” (25)

The mayfly squid’s ultra-sophisticated control over its coloration and patterns might seem inexplicable given the often limited visibility available to it. However, if the mayfly squid’s third eye does detect bioluminescence, then the evolutionary advantage of such control becomes apparent: even in the high silt conditions of the Amazon (or some of Florida’s more polluted rivers), it can remain in communication with other squid, using what amounts to a form of cryptography.