Drawing: dorsal view of female Spirula spirula. Source: Chun, 1910
Origin: Publication: Chun, C. 1910. Die Cephalopoden. Oegopsida. Wissenschaftliche Ergebnisse der deutschen Tiefsee-Expedition auf dem Dampfer "Valdivia" 1898-1899, 18 (1). 1-401.

Source: https://commons.wikimedia.org/wiki/File:Spiruladraw.png

The ram's horn squid, little post horn squid or tail-light squid (Spirula spirula) is a species of deep-water squid-like cephalopod mollusk. It is a deep-ocean dweller. The shell of Spirula is extremely light in weight, very buoyant, and surprisingly durable; it very commonly floats ashore onto tropical beaches all over the world. This seashell is known to shell collectors as the ram's horn shell or simply as Spirula.