Critter of the week: Spirula spirula
The Ram’s Horn squid (Spirula spirula) is a mesopelagic species, meaning that it lives in the mid-water column. It typically lives in dark depths of 500-1000 m in the day and migrates up to the shallows of 300 m at night, part of its diel vertical migration pattern (one of the largest daily mass migrations in the world.)
Spirula specimens have been collected from tropical and subtropical waters worldwide, and we have collected live specimens from the Challenger Plateau, east of New Zealand and just recently from the outer Bay of Plenty. As the shells are very buoyant they wash up on beaches all over the world!
This species was described by Carl Linnaeus, the father of modern taxonomy, way back in 1758. He originally named it Nautilus spirula, but it has since been transferred to the genus Spirula. Spirula shares similarities with the Nautilus, Cuttlefish and the extinct ammonites and belemnites as they all have a multi-chambered shell, rather than a pen like other types of squid.
Wikipedia goes into lots of detail about this species and our friends at the Australian Museum have produced a page with some information about them too: