Arrow Crabs “Stenorhynchus Seticornis”

Arrow crabs

Last updated on July 8th, 2022 at 01:38 pm

Arrow crabs are a type of crab that is found in the eastern United States. They are characterized by their long, thin tails and their bright blue claws. They get their name from their ability to shoot venomous arrows at predators with their claws.

They are arrow-shaped crustaceans that live in the Indian Ocean. They have a carapace that is arrow-shaped, hence their name! The arrow crab grows to be about 6 inches long and 1 inch wide at its widest point. They are often caught for food because they are delicious, but they also provide us with many other benefits.

Arrow crabs (Stenorhynchus seticornis) are found in the waters around New Zealand. They live on rocks and coral reefs at depths of up to 200 meters, but during the day they move into caves or crevices where there is less water movement. When night falls, arrow crabs emerge from their hiding places to forage for food.

They have a flattened body shape and a carapace that is colored green, blue, or brown. They have two large claws, one of which is used for catching prey while the other is used for defense. Arrow crabs can grow up to 18 centimeters in length.

Like all crabs, they have a hard outer shell known as the carapace. The front two-thirds of an arrow crab’s body is covered by this protective shell, while its abdomen and gills are located underneath.

The flat, broad shape of an arrow crab means that it can easily wedge itself into crevices or under rocks on the ocean floor. This makes them very difficult for predators to snatch them from their hiding places.

They are omnivorous animals and they eat a variety of things including algae, sponges, small fish, molluscs, and crustaceans.

Origin and descriptions

Arrow crabs

Arrow crabs are found in the Atlantic Ocean and Gulf of Mexico. They have a long, narrow body with a triangular-shaped head. They get their name from the two large spikes that extend out from their carapace. These spikes are used for defense and can be dangerous to humans.

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The carapace (shell) of the arrow crab is brownish-red to orange in color. Their legs are red and yellow, while their claws are black or blue.

They belong to the family of Inachidae and are found in the Indo-Pacific region. It has a flattened body with long spines on either side of its head and thorax. Arrow crabs are usually a dark brown or greenish color, but can also be light blue. They have two large claws used for catching prey, which they eat whole.

Species profile

Arrow crabs

The Arrow Crab is a small saltwater crustacean that is native to the Indian Ocean and the western Pacific Ocean. They are found in deep waters, living among corals or under stones near sea anemones. This species has been kept by hobbyists for several years because of its unique characteristics.

Their claws have evolved to be long, curved, and slender. Each claw has a sharp spine at the base of it which is used for defense or feeding purposes.

Scientific name

The scientific name of the arrow crab is stenorhynchus seticornis

Natural habitat

The natural habitat of the arrow crab is in brackish or saltwater environments. They are commonly found in estuaries, mangrove swamps, and tidal flats.

They can also be found in freshwater habitats, but this is less common. They are known to inhabit ponds, lakes, and rivers.

Arrow crabs care

Arrow crabs do not require a lot of care and can be kept in a small tank. They are scavengers and will eat any food that is put in the tank.

Diet and feeding

These crabs are omnivores and opportunistic feeders. They eat mainly plants, such as algae and seaweeds in the wild but they will also take crustaceans, gastropods mollusks, urchins, and sea cucumbers when they can find them.

In aquaria, they can be fed a variety of things, including chopped seafood, shrimp pellets, algae wafers, and flake food.

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They are not fussy eaters but should have a varied diet to ensure good health. Arrow crabs can also scavenge on dead fish or other animals that have died in the aquarium. Most people feed them once per day, but they can be fed up to three times per day if necessary.

Ideal water conditions

The ideal pH for the arrow crab is between seven and eight. The salinity in an aquarium with a Bi-mini top should be kept at 1 to 3.5 pounds per gallon of water, while with no cover, it can range from zero to 2 pounds per gallon depending on how much live rock is there in the tank.

The arrow crab can be kept in a reef tank as long as the salinity of the water does not go over 3 pounds per gallon.

An increase in ammonia and nitrite levels is likely to occur if an arrow crab is placed into a fish-only aquarium, but this problem can easily be solved by keeping on top of regular partial water changes.

Tank Size

A minimum tank size of 20 gallons is recommended for one crab. Larger tanks are better as they provide more space for swimming.

Tank mates

Arrow crabs can be kept with a variety of other marine animals. Some good tank mates include urchins, sea stars, hermit crabs, and snails. They are peaceful creatures and will not bother any other inhabitants of the tank.

Aquarium setup

They are not overly picky about their living conditions. For a healthy arrow crab, the water quality is more important than decorations or substrate type. Arrow crabs should be kept in an aquarium that has at least 12 inches of sand and rocks on the bottom to hide under.

They do well with live rock as long as there aren’t too many holes for them to crawl into and get trapped. They should be kept with plenty of other bottom dwellers, like a snail, to clean up any food that falls on the sand and rock substrate.

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Arrow crabs

Like all crustaceans, arrow crabs periodically molt their exoskeleton as they grow. Molting is a very stressful process for the crab and should be avoided if at all possible. They will often molt when they are stressed, such as when being moved to a new aquarium or when there is a sudden change in water conditions.

Molting can be induced by increasing the water temperature to 85 degrees F and adding a molting supplement to the water. Be sure to remove any hiding places like rocks or plants during molting, as the crab will be very vulnerable at this time. After the new exoskeleton hardens, replace any decorations in the aquarium.

If you notice your arrow crab is molting, do not feed it for a few days until it has had a chance to eat the new exoskeleton. You can also offer a vitamin supplement to help with the process.


Arrow crabs

Are arrow crabs aggressive?

No. Arrow crabs are not typically aggressive towards people. However, they will defend themselves if threatened.

How big are arrow crabs?

They can measure between one and three inches. They might appear larger because of their large claws.

Where are arrow crabs found?

They can be found in the Atlantic Ocean from Massachusetts to Brazil. They are also common in the Gulf of Mexico and the Caribbean Sea.

Are arrow crabs freshwater?

No, arrow crabs are marine animals.

Are arrow crabs reef safe?

Yes, They are reef-safe. They scavenge on dead animals and remove debris from the reef, making them helpful in keeping reefs clean.

There is something special about them that makes them a favorite among marine aquarists. Arrow crabs possess an amazing ability to change color to match their surroundings! This camouflage helps them avoid predators and hunt prey.

How long do arrow crabs live?

They can live up to six years in the wild. They are a long-lived species for their size and have been known to reach ten years of age in captivity. Arrow crabs live shorter lives in the lab, likely due to less stressful and more comfortable conditions.

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How do arrow crabs reproduce?

Arrow crabs

The female will lay her eggs on the seafloor, the female can produce over 100,000 eggs at a time and then the male arrow crabs fertilize them. The larvae spend two to three months in their planktonic stage before they settle out of ocean currents onto a suitable hard substrate such as rocks, mangrove roots, or broken shells. Once settled, these juveniles remain hidden under debris or in crevices until they mature.

Do arrow crabs eat bristle worms?

Not exactly. In fact, adult arrow crabs probably avoid bristle worms because the bristles can be very irritating to their soft bodies as they grow older and larger, however, younger arrow crabs do eat small marine invertebrates such as copepods and amphipods.

Arrow crab with clownfish

There are many symbiotic relationships between arrow crabs and other animals. A common relationship is the one that clownfish have with arrow crabs. If a clownfish finds an arrow crab on its territory, it will protect it by fighting off any predator of the crab including humans. This is because the arrow crab has a mutualistic relationship with the clownfish.