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Side view of a Spirula shell -
| Spirula Temporal range:
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|---|---|
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| Dorsal view of female | |
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| Ventral view of female (chromatophores of mantle missing) | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Cephalopoda |
| Order: | Spirulida |
| Family: | Spirulidae Owen, 1836 |
| Genus: | Spirula Lamarck, 1799 |
| Species: | S. spirula
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| Binomial name | |
| Spirula spirula | |
| Synonyms | |
Spirula spirula is a species of deep-water squid-like cephalopod mollusk. It is the only extant member of the genus Spirula, the family Spirulidae, and the order Spirulida. Because of the shape of its internal shell, it is commonly known as the ram's horn squid[3] or the little post horn squid. Because the live animal has a light-emitting organ, it is also sometimes known as the tail-light squid.
Live specimens of this cephalopod are very rarely seen because it is a deep-ocean dweller. The small internal shell of the species is, however, quite a familiar object to many beachcombers. The shell of Spirula is extremely light in weight, very buoyant, and surprisingly durable; it very commonly floats ashore onto tropical beaches (and sometimes even temperate beaches) all over the world. This seashell is known to shell collectors as the ram's horn shell or simply as Spirula.
- ^ Hayward, B.W. (1977). "Spirula (Sepioidea: Cephalopoda) from the Lower Miocene of Kaipara Harbour, New Zealand (note)" (PDF). New Zealand Journal of Geology and Geophysics. 19: 145–147. doi:10.1080/00288306.1976.10423557.
- ^ Barratt, I. & Allcock, L. (2012). Spirula spirula. The IUCN Red List of Threatened Species. Version 2014.2.
- ^ Norman, M. 2000. Cephalopods: A World Guide. Hackenheim, ConchBooks.