Frilly arrow crab

The Frilly Arrow Crab (Stenorhynchus seticornis, also called spiny or decorator arrow crab) is a striking, long-legged crustacean from the Caribbean and Western Atlantic. Identified by its triangular body, elongated rostrum, and spiky “frilly” carapace, this nocturnal invert prowls reef crevices hunting bristle worms, small worms, leftover meaty foods, and detritus. In captivity, it thrives in a reef or FOWLR aquarium of 20–30+ gallons with stable parameters (SG 1.024–1.026, pH 8.1–8.4, 76–80°F), moderate flow, and lots of rockwork. Provide iodine-rich, high-quality water to support molting, and avoid copper-based medications.

Behavior is semi-aggressive/predatory: while helpful at controlling bristle worms, a frilly arrow crab may harass small shrimp (sexy, anemone, juvenile cleaners) or very tiny fish, especially if underfed. Feed mysis, chopped shrimp, clam, and pellets several times per week to reduce opportunistic hunting. Keep one per tank unless it’s a known mated pair; males can fight. SEO keywords: frilly arrow crab care, Stenorhynchus seticornis, arrow crab reef safe, bristle worm control, arrow crab diet, arrow crab molting, reef invertebrate compatibility, Caribbean reef invert, nano reef clean-up crew, FOWLR invertebrates.