TankBud

Arrow crab

Stenorhynchus seticornis

Also known as Yellowline Arrow Crab, Arrowhead Crab, Spider Crab

SaltwaterCrab

Arrow crab (Stenorhynchus seticornis)
NOAA · Public domain

Care at a glance

Temperature
72–79°F
22–26°C
pH
8.1–8.4
Adult size
3.9 in
10 cm
Minimum tank
30 gal
115 L
Temperament
Mostly peaceful
Social behavior
Solitary
Own kind
One per tank
Tankmates
With caution
Swim level
Bottom
Diet
Carnivore
Difficulty
Easy
Breeding
No record
Rarity
Common
Reef safe
Reef safe with caution
Family
Inachidae
Origin
Western Atlantic, from North Carolina and Bermuda south to Brazil, including the Caribbean Sea

Overview

The arrow crab is a long-legged spider crab that hunts bristleworms in a saltwater tank. It is easy to keep.

Did you know

The arrow crab actively avoids light and moves to a shadier spot when disturbed. It often seems to migrate to a new cave every few days as it hunts for cover away from the aquarium lights.

Caring for the arrow crab

Give an arrow crab at least 30 gal (115 L), with plenty of three-dimensional rockwork. Build in tunnels, ledges and holes for it to retreat into during the day. Keep the water at 72 to 79°F (22 to 26°C) with a pH of 8.1 to 8.4.

It preys on bristleworms, using its long legs to reach into crevices and pull the worms free. It strips off the bristles before eating them. It will not fully clear a bristleworm population, since plenty stay out of reach in the rock and sand. It still puts a real dent in the numbers.

The arrow crab is mostly peaceful and stays fairly mild-mannered while small. As it grows, it becomes a more capable hunter. It will then catch and eat small, slow fish, ornamental shrimp, snails and feather duster worms if it can reach them.

That habit gives it a reef safe with caution rating in a reef with delicate tank mates. Keep one per tank, since it can be territorial toward its own kind and other crabs.

Good to know

Stenorhynchus seticornis is a spider crab in the family Inachidae, named for its long, pointed, forward-tapering snout. The triangular carapace reaches about 6 cm, and the long, thin walking legs spread much wider. Its body is pale tan to yellow, with fine red-brown stripes running down the legs. Like several spider crabs, it can decorate itself with bits of algae or debris for camouflage.

In the wild

The arrow crab is found throughout the western Atlantic, from North Carolina and Bermuda south to Brazil, including the Caribbean Sea. It lives on coral reefs and rubble from the shallows down to around 10 meters. It is nocturnal and shelters by day in small caves and crevices. At night it comes out to hunt across the rockwork on its long, spindly legs.

Common questions

What size tank does an arrow crab need?

An arrow crab needs at least 30 gal (115 L). It spends most of its time in the bottom.

What temperature and pH does an arrow crab need?

An arrow crab is comfortable at 72–79°F (22–26°C) with a pH of 8.1–8.4.

What does an arrow crab eat?

An arrow crab hunts bristleworms, pulling them from crevices and stripping off the bristles before eating them. A grown one will also catch small, slow fish, ornamental shrimp, snails and feather duster worms.

How big does an arrow crab get?

An adult arrow crab reaches about 3.9 in (10 cm).

Related species