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.

Here’s a video link to tell you more about the Ram’s Horn 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:

Australian museum


[Sadie Mills, NIWA]

Have you ever seen these white spirally shells washed up on your local beach?
Have you ever wondered what animal makes these shells or even if there is something living inside? The purple shells belong to Janthina sp., a hermaphroditic snail that spends its whole life floating around on the sea surface on a bubble raft of its own making, eating jellyfish! (

[Owen Anderson, NIWA Vulnerable Deep Sea Communities]

The white spiralling shell is actually the internal shell of the Ram’s Horn Squid, scientific name Spirula spirula. You can just see the edge of the shell poking out of the mantle wall. The animal pictured is an adult, these animals rarely get bigger than 45 mm mantle length and only live for a year and a half. You can see its live colouration here. We collected this specimen on our recent Bay of Plenty voyage.

[Sadie Mills, NIWA Vulnerable Deep Sea Communities]

The internal shell, just about seen here poking out on either side of the mantle, is actually a buoyancy organ. It helps the animal to orient its head downwards and keep the body vertical.

[Sadie Mills, NIWA]

The buoyant shells wash up on beaches all over the world, but the squid itself is rarely seen. The shell is made up of a series of separate chambers. These are gas filled and the amount in each chamber can be varied allowing the squid to rise or descend through the water column – check out more about its diel vertical migration pattern from the depths during the day to the shallows during the night on Wikipedia.
Ram's Horn Squid (Spirula spirula) Shell. [Sadie Mills, NIWA]