The deep sea contains alien‑like animals whose strange forms are survival adaptations. This article highlights 15 species — from the frilled shark with a 3.5‑year pregnancy to the 13‑ft leg‑span Japanese spider crab and the bioluminescent anglerfish — and explains how each is adapted to life in darkness and high pressure. ROVs and deep‑sea research continue to reveal surprising behaviors and evolutionary history.
15 Alien‑Looking Deep‑Sea Creatures — Strange Adaptations from the Ocean's Depths
The deep sea contains alien‑like animals whose strange forms are survival adaptations. This article highlights 15 species — from the frilled shark with a 3.5‑year pregnancy to the 13‑ft leg‑span Japanese spider crab and the bioluminescent anglerfish — and explains how each is adapted to life in darkness and high pressure. ROVs and deep‑sea research continue to reveal surprising behaviors and evolutionary history.
18:58, 07.11.2025Science
The deep ocean is home to a host of bizarre, otherworldly animals whose strange shapes and behaviors are adaptations that let them survive cold, pressure and perpetual darkness. Advances in remotely operated vehicles (ROVs) and deep‑sea imaging have given scientists rare glimpses of these elusive species, revealing evolutionary strategies from extreme gestation to bioluminescent lures.
1. Frilled shark
Chlamydoselachus anguineus is often called a living fossil. Its frilly gills and elongated body recall ancient relatives, and females carry embryos for about 3.5 years — one of the longest known gestations among vertebrates (2020 study). Frilled sharks inhabit parts of the Atlantic and Pacific, reach at least 6 feet, and feed mainly on squid and fish.
2. Hagfish
Hagfish are scavengers that burrow into decaying carcasses using tooth‑like structures. Roughly 76 species exist, some living as deep as 5,600 feet. Known as "slime eels," they secrete copious mucus to deter predators; researchers are exploring industrial and medical uses for that gel, including wound treatments. Sizes range from a few inches to about 4 feet.
3. Goblin shark
The goblin shark is a rarely seen bottom dweller with a long, flattened snout and a jawful of specialized teeth (about 53 upper and 62 lower in some counts). It captures prey by "slingshot feeding," rapidly protruding its jaws — a motion recorded at nearly 7 mph — to snatch fish, crustaceans and squid (2016 observation).
4. Vampire squid (Vampyroteuthis infernalis)
Despite its name, the vampire squid is neither a true squid nor an octopus and occupies its own taxonomic group. Living around and below ~2,000 feet in the mesopelagic zone, it subsists largely on marine snow (drifting organic matter). Its webbed arms form a cloak‑like silhouette, and when threatened it can emit a cloud of bioluminescent mucus.
5. Sarcastic fringehead
A small but aggressive tube blenny native to the Pacific (California to Mexico), the sarcastic fringehead displays an extraordinary threat ritual: it opens a fluorescent‑rimmed mouth wide to warn rivals. Typically 3–8 inches long, these fish inhabit abandoned worm tubes and even discarded cans.
6. Ghost shark (chimaera)
Chimaeras, commonly called ghost sharks, are cartilaginous fish related to sharks and rays but on a distinct evolutionary branch. They have a sensitive snout for detecting electric fields and a venomous spine near the dorsal fin. Fossils trace their lineage back hundreds of millions of years, and new species continue to be described — though some may face extinction before they're fully studied.
7. Blobfish
Members of the fathead sculpin family, blobfish live between roughly 330 and 9,200 feet. Their gelatinous tissues are supported by water pressure at depth; when brought to the surface they appear saggy, which led to their infamous "world's ugliest animal" title in a 2013 poll. The jelly‑like body helps them maintain buoyancy without a swim bladder.
8. Atlantic wolffish
The Atlantic wolffish has robust, canine‑like teeth for crushing scallops, hermit crabs and sea urchins. Found off North America's Atlantic coast down to about 1,640 feet, it produces antifreeze‑like compounds that prevent internal ice formation in cold water. Adults typically measure around 3 feet and can reach up to about 5 feet in some reports.
9. Japanese spider crab
One of the largest arthropods, Macrocheira kaempferi has a body roughly 15 inches across and legs that can span up to 13 feet; individuals may weigh as much as 44 pounds. These crabs are primarily scavengers and are often observed missing limbs. Lifespan estimates vary, with some suggestions they may live decades, possibly up to 50–100 years.
10. Anglerfish
Anglerfish (>200 species) inhabit a wide range of depths. Female deep‑sea anglerfish bear a bioluminescent lure — a modified dorsal fin filament tipped with glowing bacteria — that attracts unwary prey. In many species, tiny males permanently fuse to females as parasitic mates, providing sperm in exchange for nutrition.
11. Grenadiers (rattails)
Grenadiers are a diverse family of deep‑sea fish (300+ species) found worldwide down to about 13,100 feet. Many have gelatinous tissues and less dense musculature to aid buoyancy. Large eyes help them detect bioluminescent prey, and when hunting fails they often scavenge by scent.
12. Barreleye
The barreleye fish features a transparent, fluid‑filled cranial shield and large, tubular, green‑tinted eyes. Studies at the Monterey Bay Aquarium Research Institute showed these eyes can rotate to look upward for prey or forward to inspect captured food. The clear dome likely protects the eyes from the tentacles of prey such as siphonophores.
13. Deepwater lizardfish
Two species (Bathysaurus mollis and B. ferox) are known as deepwater lizardfishes; B. mollis has been recorded as deep as 16,085 feet. These ambush predators exceed 2 feet in length, have large eyes and many sharp teeth, and have been reported to exhibit cannibalism.
14. Slender snipe eel
Slender snipe eels can reach about 4 feet in length while weighing only a few ounces. Their ribbon‑like bodies contain roughly 750 vertebrae, and a long, narrow snout with inward‑curving teeth suggests a feeding method where small crustaceans snag on the jaws as the eel swims with its mouth open.
15. Sloane's viperfish
Sloane's viperfish inhabits the mesopelagic "twilight" zone (roughly 650–3,300 feet) and undertakes vertical migrations to feed. Growing to about 10 inches, it traps prey with long, fang‑like teeth and can unhinge its jaws to swallow relatively large meals. Photophores on its underside produce blue‑green and yellow light that help camouflage it from predators below, and some species use a bioluminescent lure to attract prey.
Why these animals matter: Each species illustrates a unique evolutionary answer to the challenges of darkness, cold and pressure. ROVs and deep‑sea cameras are expanding our knowledge, but much of the ocean's depths remain unexplored — and full of surprises.
Sources: National Oceanic and Atmospheric Administration (NOAA); Monterey Bay Aquarium Research Institute (MBARI); Natural History Museum, London; Australian Museum; Smithsonian Institution; Woods Hole Oceanographic Institution; University of Texas Marine Science Institute; Hawaii Division of Aquatic Resources; state and regional fisheries agencies; academic studies cited within the text.
Originally published April 2018; updated November 2025.