You can't find them at PETCO and they won't bring the emotional gratification of a real pet's affection, but if you're itching to replace kibble and fish flakes with batteries and power cords, check out these robot animals.

Robot Dog
Roboticus lupus familiaris

Straight from the Land of the Rising Sun, the DIY G-Dog kit, by HPI, is Japan's cyber substitute for man's best friend. At a mere 5.3" tall, it's the perfect companion for HPI's 9-inch-tall humanoid robot (um, creepy much?), the GR-001.

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G-Dog includes motion processing software, a three-axis acceleration sensor, and a wireless remote. But for $1,000, you'd think it could at least play fetch. Or bring you the morning paper. Or bark.

[More Info via Gizmodo]

Robot Fish
Roboticus carpio

These self-guided robot fish, unveiled at the London Aquarium in March, were developed by scientists at Essex University.

The research team spent three years developing a "biologically inspired" robot that mimics the undulating motion of real fish. The battery-powered robo carp use artificial intelligence and built-in sensors to avoid obstacles and respond to environmental changes.

On top of being just plain cool, engineers say the fish robots have practical applications too. They hope their invention will help with seabed exploration, detecting oil leaks, mining countermeasures, and improving the performance of underwater vehicles.

[More Info via Essex University]

Robot Cat
Roboticus felis

This robot cat, which goes by "Biobot," uses sensors in its whiskers to respond to its environment by avoiding obstacles and interacting with objects and people.

Robot Elephant
Roboticus elephantidae

Built in 2005, the Sultan's Elepehant was designed by a French theatre company for the centennial celebration of Jules Verne's death.

Designed by François Delarozière, The Sultan's Elephant is mostly wood and operated by a combination of hydraulics and motors. The functional, water-spraying trunk contained over 22 pistons alone.

The original Sultan's Elephant was roughly three stories tall and weighed over 50 tons. Sadly, it no longer exists, although a 20 foot replica is on display at the Machines of the Isle of Nantes exhibition in Nantes, France.

[Official Site of The Sultan's Elephant]

Robot Spider
Roboticus arachnida

Designed by yet another French performance art group, this 50-foot, 37 ton spider (nicknamed "La Princesse") cost £1.8 million (roughly $3 million US) to build.

La Princesse has 50 axes of movement and requires 16 cranes, six forklifts, eight cherry pickers, and over 250 people to operate. It includes seven special effects, including rain, fire, smoke, wind, snow, light, and sound.

The steampunk arachnid is currently on display in Yokohama, Japan. We just hope she's not teaming up with Mothra or Kumonga, otherwise: we're screwed.

[More Info via BBC]

Robot Snake
Roboticus serpentes

This "amphibious snake-like robot," known as ACM-R5, was designed at the Hirose Fukushima Lab in Tokyo, Japan.

The snake's body is equipped with paddles and wheels to propel itself forward. Meanwhile, its control system features independent CPUs, batteries, and motors in each joint unit, allowing operators to remove, add, and exchange units for different situations.

In other words, like an earthworm or a hydra, you can chop it into several pieces and it'll just keep on going.

But hey, wait a minute — what about those paddles we mentioned. What on Earth could a terrestrially bound robot serpent need paddles for? Well, since you asked...

[Official ACM-R5 Website]

Robot Snake
Roboticus serpentes

This mofo can can swim, too! ACM-R5 isn't just a scary land robot, it's also a terrifying aquatic one.

ACM-R5 is like the T-800 of robot animals. It doesn't feel pity, or remorse, or even aquaphobia. And like a Terminator, this scary seadragon will not stop, ever, until you are dead.

(Well, that or until its battery runs out.)

[Official ACM-R5 Website]

Robot Mule
Roboticus equus mulus

Meet BigDog. The name is kind of a misnomer, since it actually looks more like a weird, headless alien mule.

In reality, BigDog actually was modeled after mules. Its designers — an American engineering firm called Boston Dynamics — developed the robot as a mechanical pack mule meant to accompany military soldiers in traversing rough terrain that would challenge conventional vehicles' wheels, tires, and treads.

[Official Site]

Robot Grasshopper
Roboticus caelifera

Researchers in Switzerland designed this robot grasshopper, which — with its 5 centimeter stature and a whopping weight of 7 grams — can jump 27 times its own height.

Scientists hope the robot grasshoppers can be used to explore disaster areas or even the surfaces of other planets by hopping over otherwise insurmountable obstacles.

[More Info via Endgadget]

Robot Penguin
Roboticus sphenisciformes

These German-engineered bionic penguins have one ability their sentient counterparts don't: flight.

The penguins use their flippers to paddle and maneuver through the water and, when they're filled with helium, the air. They also use a 3D sonar system to monitor their surroundings and avoid collisions.

[More Info via Daily Mail UK]

Robot Gecko
Roboticus gekkonidae

Stickybot is a gecko-like robot developed by researchers at Stanford University.

Another "climbing robot," Stickybot uses synthetic setae (the tiny hairs on real geckos' feet) and intermolecular forces to scale vertical surfaces.

[Official Website]

Robot Jellyfish
Roboticus cnidaria

AquaJelly is a radio-controlled robot jellyfish designed by the same German scientists who created the bionic penguins.

The battery-powered jellyfish rely on several of the same properties as real jellyfish to guide their motion and, yes, like the penguins — there's a flying, helium-filled version, too.

[More Info via Gizmodo]