White-stripe Urchin Shrimp

Stegopontonia commensalis

Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Family: Palaemonidae
Genus: Stegopontonia
Species: Stegopontonia commensalis

The white-stripe urchin shrimp (Stegopontonia commensalis) is a long, needle-thin shrimp that lives along the spines of sea urchins, striped to match them. Its dark body has a pale stripe running from head to tail.

Reaching about 2-3 cm, it lies flat along a single spine of its host, usually a Diadema or Echinothrix urchin, and moves from spine to spine to stay hidden. It feeds on particles and tissue from the urchin's surface.

Long-spined urchins on reefs and sandy slopes in the Philippines often host this shrimp. Look carefully along the spines, without touching them, to find it.

Photo: 呂一起(Lyu yi-chi), CC BY 4.0, via iNaturalist