Arrow Crab

Quick facts

Handling caution: Sharp, pointed claws can pinch; not venomous

Identity

Also known as

Yellowline Arrow Crab; Spider Crab

Synonyms

Stenorhynchus sagittarius

Environment

Saltwater

Native to

Western Atlantic, Caribbean Sea, Gulf of Mexico, Bermuda, Brazil

Habitat

Shallow coral reefs, rocky crevices, tide pools, and sand flats at depths of about 3-30 m, often sheltering near sea urchins or anemone tentacles.

Sourcing

Wild-caught

Conservation

Not Evaluated

Care

Care level

Easy

Temperament

Semi-Aggressive

Adult size

2 – 6 in (5.1 – 15 cm)

Lifespan

2 – 5 yrs

Min tank

30 gal (114 L)

Growth rate

Slow

Placement

Rock & glass

Water

Temperature

72 – 78 °F (22 – 26 °C)

pH

8.1 – 8.4

dKH

8 – 12 dKH

Salinity

1.023 – 1.025 SG

Flow

Moderate

Behavior & compatibility

Social

Solitary

Aggression to own kind

High

Active

Night

Reef safe

With caution

Invert safe

With caution

Shrimp safe

With caution

Clean-up role

Pest control, Detritus, Leftover food

Population boom risk

Low

Feeding & breeding

Diet

Carnivore

Foods

Frozen, Live, Freeze-dried, Pellets, Flakes

Breeding type

Direct development

Breeding difficulty

Not bred in captivity

Sexing

Females are noticeably smaller than males and may carry visible egg masses under the abdomen when berried; otherwise sexes look similar.

Target feeding

Beneficial

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Care guide

Overview

Arrow crabs are long-legged spider crabs whose slender, triangular body and stilt-like walking legs give them their name and a cream, brown, and yellow-striped coloring. It stays wedged in rock crevices by day, emerging at night to scavenge, and molts periodically, requiring stable water chemistry and abundant hiding spots. Keep singly, as males fight, and feed regularly to curb any pecking at small tankmates or coral polyps.

Care

A long-legged spider crab that spends daylight hours wedged into rock crevices and becomes active after lights out. It needs mature live rock riddled with caves and overhangs, both for daytime shelter and as a refuge during molting, when it is soft and defenseless. Stable water chemistry matters more than exact numbers; sudden swings in salinity or pH stress this species more than slow drift.

Feeding

Naturally an opportunistic scavenger and predator, picking apart bristleworms, feather duster worms, and small invertebrates it can catch. In captivity it readily takes meaty frozen foods like mysis, shrimp, and clam, along with sinking pellets, and will scavenge uneaten fish food from the substrate. Feed several times a week; a hungry arrow crab is far more likely to turn on tankmates or peck at coral polyps.

Tank mates

Best paired with fish too large or fast to be caught, since slow-moving or small fish and shrimp can become prey. Two males housed together will fight, often fatally, so keep only one per tank unless the aquarium is very large with abundant hiding spots. It is generally left alone by larger reef fish and can coexist with most corals if well fed, though a starved individual may pick at polyps.

Breeding

Females carry fertilized eggs attached to the underside of the abdomen until they hatch into free-swimming larvae after roughly two weeks. The planktonic larvae require open-ocean rearing conditions that are impractical to replicate in a home aquarium, so captive breeding is essentially unheard of. Specimens in the trade are collected from the wild rather than tank-raised.

Health

Molting is the main period of vulnerability, since the crab is briefly soft-shelled and an easy target for tankmates; leaving the shed exoskeleton in the tank lets it reclaim minerals by eating it. Copper-based medications are lethal and must never be dosed in a system housing this crab. Poor water quality or high nitrate and phosphate levels can interfere with successful molting.

Sources

1. Arrow Crab (Stenorhynchus seticornis) Aquarium Care | Atlarium
2. A Guide To Arrow Crab Care
3. Arrow crab: aquarium care, feeding, compatibility & facts
4. Arrow Crab: Saltwater Aquarium Invertebrates – LiveAquaria