Normalmente vive all'interno delle oloturie ove si rifugia infilandosi di coda nell'orifizio anale

Tassonomia:

Domain: Eukaryota - Whittaker & Margulis,1978 - eukaryotes
Kingdom: Animalia - C. Linnaeus, 1758 - animals
Subkingdom: Bilateria - (Hatschek, 1888) Cavalier-Smith, 1983
Branch: Deuterostomia - Grobben, 1908
Infrakingdom: Chordonia - (Haeckel, 1874) Cavalier-Smith, 1998
Phylum: Chordata - Bateson, 1885 - Chordates
Subphylum: Vertebrata - Cuvier, 1812 - Vertebrates
Infraphylum: Gnathostomata - auct. - Jawed Vertebrates
Superclass: Osteichthyes - Huxley, 1880 - Bony Fishes
Class: Osteichthyes - Huxley, 1880 - Bony Fishes
Subclass: Actinopterygii - Ray-Finned Fishes
Infraclass: Actinopteri
Cohort: Clupeocephala
Superorder: Paracanthopterygii
Order: Ophidiiformes - Cusk Eels
Family: Carapidae - Pearlfishes
Subfamily: Carapinae
Genus: Carapus - Rafinesque, 1810
Specific name: acus - (Brünnich, 1768)
Scientific name: - Carapus acus (Brünnich, 1768)