Arrow crab (Stenorhynchus seticornis) care guide

Group
Other invertebrates
Other names
Yellowline arrow crab, Caribbean arrow crab, Cancer seticornis
Family
Inachidae
Origin
Western Atlantic from North Carolina and Bermuda to Brazil, including the Caribbean; reefs at about 3–9 m and deeper
Water
saltwater
Maximum size
15 cm
Temperature
22–26°C
pH
8.1–8.4
Hardness
SG 1.020–1.025, dKH 8–12
Minimum tank
150 litres
Care level
beginner
Temperament
semi_aggressive
Reef safe
with_caution

Care

The arrow crab is a spider crab with a narrow, pointed triangular body (the "arrow"), up to about 6 cm long, and very long, thin legs spanning 10–15 cm or more. The body is golden, yellow or cream with brown, black or iridescent blue lines; the legs are reddish or yellow and the slender claws blue or violet. Females are often much smaller than males. Family placement varies between sources (Inachidae or Majidae). Set-up: a tank of 150 litres or more with rockwork it can climb. It is mostly nocturnal and territorial, and it decorates itself with small organisms for camouflage. Keep one per tank; two males will fight. Role: it is often bought to control bristle worms, and it will eat smaller ones. It also scavenges leftover food. It is not a gentle clean-up animal, though: it eats small feather duster worms, may attack shrimp (even banded coral shrimp) and small, slow fish, and if hungry may pick at mushrooms and polyps. In the wild it often lives among the tentacles of the Caribbean anemone Lebrunia danae and has been seen cleaning fish. Copper: copper-based medicines and some plant fertilisers are toxic to shrimp, snails and most invertebrates. Never dose copper in a tank holding this animal, and check fertiliser and medicine labels before use. Sources: LiveAquaria (liveaquaria.com/products/arrow-crab); Wikipedia (en.wikipedia.org/wiki/Stenorhynchusseticornis). Checked October 2026.

Diet

Opportunistic carnivore and scavenger. Takes small invertebrates such as bristle worms and feather dusters, plus frozen mysis, krill, chopped seafood, pellets and flake. Feed a few times a week so it is less likely to hunt tankmates or pick at polyps.

Breeding

The male passes a sperm packet to the female, who fertilises her eggs and carries them on her abdomen until they hatch as planktonic zoea larvae. Larger females carry more eggs. The larvae need plankton and marine water and are not raised in home aquariums.

Compatibility and tank mates

Fine with medium and large fish that will not eat it. Risky with shrimp, small crabs, feather dusters, small gobies and blennies and sleeping small fish. Usually leaves stony corals alone but may pick at mushrooms and polyps when hungry. Triggers, puffers and large wrasses may eat it.

Last updated 8 October 2026. Community-edited care guide on Aquatic-Auctions.

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