Octopuses are a fascinating group of cephalopods that come in many shapes, sizes, and colors. Most octopuses are quite common, living in shallow waters near coastlines. However, some species are incredibly rare, only known from a handful of specimens. Determining the absolute rarest octopus species is challenging, but contenders for the title include the Seven-arm Octopus, the Frilled Octopus, and the Dumbo Octopus.
The Seven-arm Octopus
One of the rarest and most mysterious octopuses is the Seven-arm Octopus (Haliphron atlanticus). As the name suggests, these octopuses naturally only have seven arms instead of the usual eight. The seven-arm octopus was first discovered in the 1950s off the coast of Florida. Since then, only a few additional specimens have ever been found.
In April 2021, researchers reported finding only the third-ever seven-arm octopus in the Gulf of Mexico. The first specimen was found in 1953 and described in 1956. Over 60 years passed before the second specimen was discovered in 1998. Encountering a third individual after a 20+ year gap highlights just how rarely these octopuses are seen.
Some key facts about the seven-arm octopus:
| Species | Haliphron atlanticus |
| Arms | 7 |
| Size | Up to at least 61 cm (2 ft) long |
| Habitat | Deep ocean, over 1,000 m (3,300 ft) depth |
| Known Specimens | 3 |
The seven-arm octopus inhabits deep waters of the ocean, far offshore. Their habitat range appears to include the Gulf of Mexico, the Atlantic Ocean near Florida, and perhaps the Caribbean Sea as well based on past captures. They have been found at depths of over 1,000 meters (3,300 feet).
The extreme habitat makes this octopus very difficult to study. Little is known about their life history, ecology, reproduction, or behavior. Since they live so deep, seven-arm octopuses have only been captured a handful of times over decades of surveys. Clearly, encountering one is incredibly rare.
Some scientists theorize that the seven-arm octopus loses one arm through a developmental abnormality. Other octopus species are known to occasionally have fewer or greater than eight arms, though having seven arms appears especially unusual. The origins of the seven-arm octopus remain highly mysterious given so few specimens to study.
Frilled Octopus
The frilled octopus (Opisthoteuthis californiana) is an unusual octopus that lives in the deep Pacific Ocean, mainly off the coasts of California and Hawaii. It gets its name from having fleshy, frilly skin between its arms that resembles a frilled dress or collar.
Here are some key characteristics of the frilled octopus:
| Species | Opisthoteuthis californiana |
| Arms | 8 |
| Size | Up to 60 cm (2 ft) long |
| Habitat | Deep ocean, 400-1500 m (1300-4900 ft) depth |
| Range | Northeast Pacific (California to Hawaii) |
The frilled octopus lives in the dark bathypelagic zone of the ocean, preferring depths of 400-1500 meters. They have been found off the coasts of Japan and Australia as well, though apparently in low abundances. Overall, the frilled octopus has a relatively small range concentrated in the Pacific Ocean.
As with many deep sea creatures, the frilled octopus is rarely encountered by humans. Little is known about its life history and ecology. Estimating its population size is nearly impossible given the infrequency of seeing them. Finding a frilled octopus is a very rare event. In 2017, researchers conducted a month-long deep sea submarine dive near Hawaii. Of the around 100 octopuses seen, only one frilled octopus was spotted.
The frilled octopus was first scientifically described in 1881 based on a single damaged specimen. Over a hundred years passed before more specimens were found and studied in the 1990s. The biology and behavior of this octopus remains poorly documented due to so few encounters. Clearly, the frilled octopus qualifies as one of the rarest octopus species on the planet.
Dumbo Octopus
The dumbo octopus (Grimpoteuthis spp.) is another incredibly rare deep sea creature. It is nicknamed the “dumbo” octopus due to having ear-like fins that resemble elephant ears. Dumbo octopuses inhabit extreme deep ocean environments up to 4,800 m (16,000 ft) down. At these crushing depths, the pressure can reach over 1000 times the pressure at sea level.
Several different species of dumbo octopus have been identified, but they are incredibly hard to find and study:
| Species | At least 13 known species |
| Arms | 8 |
| Size | 20-100 cm long (8-39 in) |
| Habitat | Deep ocean, below 2000 m (6600 ft) |
Dumbo octopuses have a nearly global distribution, having been found in oceans worldwide. Yet despite their broad range, actually encountering them is extremely rare. The extreme depths they live at makes them incredibly hard to observe and study.
Most dumbo octopus specimens are actually collected from accidental catches in deep trawls and dredges. Researchers cannot specifically seek out and capture them since they live so incredibly deep. No population estimates exist for any dumbo octopus species given how uncommonly they are found.
In 2020, scientists reported capturing only the third-ever specimen of Grimpoteuthis plena, one dumbo octopus species. This highlights just how few of these deep sea octopuses have ever been available for study. Their mysterious lives in the abyss make them extraordinarily rare finds.
Why Are These Octopuses So Rare?
The seven-arm, frilled, and dumbo octopuses owe their rarity to the extreme habitats they live in. All three are deep sea species living hundreds to thousands of meters down in the ocean. The cold, high-pressure, and lightless conditions of the deep make them incredibly hard to access and study.
Key reasons these octopuses are so rarely encountered include:
| – Extreme ocean depth ranges |
| – Small total population sizes |
| – Limited range (e.g. frilled octopus) |
| – Hard-to-access habitats |
| – Difficulty of deep sea exploration |
The total population sizes of these octopus species are likely very small. Compounded by inhabiting a fairly narrow portion of the ocean, the odds of encountering one are astronomically low. Active searching for them is nearly impossible given the technical challenges of deep sea exploration.
Most specimens are found through accidental capture in deep trawl nets and dredges. Very few dedicated scientific surveys have successfully located any of these species. We have so little information about their ecology because seeing them at all is incredibly rare.
Other Rare Octopus Species
In addition to the seven-arm, frilled, and dumbo octopuses, several other octopus species likely qualify as exceptionally rare:
– Sydney Octopus (Octopus tetricus) – Known from less than 10 specimens, lives off Australia
– East Pacific Red Octopus (Octopus rubescens) – Restricted to a small range, never abundant
– Cloudy Octopus (Octopus digueti) – Only a few recorded specimens from Mexico
– Common Vampire Squid (Vampyroteuthis infernalis) – Uncommon deep sea species, lives 600-1200 m down
– Star-sucker Pygmy Octopus (Octopus wolfi) – Found in a few locations in the Caribbean
– California Giant Octopus (Enteroctopus dofleini) – Hunted by early commercial fisheries, now rare
– Mimic Octopus (Thaumoctopus mimicus) – Only recently discovered, range limited to Indonesia
– Octopus chierchiae – Single specimen known, awaiting proper scientific description
These octopuses show that rarity in the octopus world takes different forms. Some have very small total populations while others are constrained to small ranges. Hunting pressure and loss of habitat have also driven down numbers of some larger shallow water octopus species. All demonstrate that many unusual octopuses remain incredibly rare in the depths or remote corners of the oceans.
Why Study Rare Octopuses?
Researchers are highly interested in rare octopuses for several reasons:
| – Learn about unique adaptations |
| – Understand ecology of extreme habitats |
| – Explore octopus biodiversity |
| – Monitor responses to climate change |
| – Evaluate conservation needs |
Rare octopuses showcase amazing adaptations for living in the deep sea, like the ear-like fins of the dumbo octopus. Studying their ecology sheds light on habitats that are difficult for humans to access, like hydrothermal vents.
Documenting the many rare octopus species also helps complete the tree of octopus biodiversity. Several new species are still being discovered even today. Tracking and protecting rare species helps assess global octopus conservation needs.
Because conditions in the deep sea are relatively stable, scientists think deep sea octopuses may be quite sensitive to changing ocean temperatures, oxygen levels, and food availability. Their responses to climate change effects could therefore serve as early warning indicators.
All these reasons underscore the importance of documenting and understanding even the rarest octopus species on Earth. Each one has an important story to tell about octopus adaptations, deep ocean ecology, and changes impacting life in the oceans.
Conclusion
The rarest octopus species occupy a fascinating realm of the ocean. The seven-arm, frilled, and dumbo octopuses stand out for their incredibly low rates of encounter. Many other octopuses are also considered exceedingly rare due to small populations, restricted ranges, or disappearing habitats.
Rarity makes these octopuseschallenging to conserve and study. Yet each one represents a unique component of octopus biodiversity. Uncovering their secrets informs many scientific fields – from evolutionary biology to marine ecology to ocean change impacts. Protecting these rare creatures and the habitats they depend on must be a priority going forward.
