Stenorhynchus seticornis

Distinguished from other arrow crabs by the combination of triangular body, long serrate rostrum, and violet-tipped claws. The variable coloration with iridescent-blue lines and specific association with anemones aids field identification. Similar decorator crabs lack the extreme rostrum elongation.

Body triangular in shape with a rostrum extended into a long point bearing serrate edges. Legs long and slender, spanning up to 10 cm. Carapace length up to 6 cm. Coloration variable: body golden, yellow, or cream with brown, black, or iridescent-blue lines; legs reddish or yellow; claws blue or violet, often with violet tips.

Shallow subtidal environments on rock bottoms, coral reefs, calcareous algae, and soft sediments including shelly gravel and sand. Depth range 3–9 m. Frequently found among the pseudotentacles of the sea anemone Lebrunia danae, often in groups of 1–6 individuals.

Western Atlantic Ocean from North Carolina and Bermuda to Brazil, including the Caribbean Sea. Restricted to the Occidental Atlantic.

Breeding period regulated by seasonal water temperature and sunlight duration; exact timing varies with latitude.

Small feather duster worms and other coral reef invertebrates.

• Lebrunia danae - commensalFrequently inhabits anemone pseudotentacles; groups of 1–6 individuals observed in south-eastern Brazil

Eggs fertilized using spermatophore deposited by male; carried on female pleopods until hatching into zoea larvae. Larvae swim to surface, feed on plankton, and undergo serial molts before metamorphosis to adult form. Larval morphology differs between shallow and deep water in maxilla endopodite setation.

Nocturnal and territorial; displays negative phototaxis, changing location between day and night. Decorates body with attached materials for camouflage or aposematic defense. Has been observed engaging in cleaning symbiosis with reef fish, moray eels, and squirrelfish in Brazilian waters.

Predator of small invertebrates on coral reefs; serves as prey for moray eels and squirrelfish. Cleaning symbiosis with fish may provide mutualistic benefits.

Commonly kept in reef aquariums to control bristle worm populations.

• Inachus phalangiumSimilar sperm morphology with five lateral arms on spermatozoa; distinguished by body shape and habitat
• Other decorator crabs (Majoidea)Share decorating behavior but lack the elongated serrate rostrum and triangular body profile of S. seticornis

• marine
• nocturnal
• coral reef
• commensal
• aquarium trade
• western Atlantic

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life