PAUL D STEWART / SCIENCE PHOTO LIBRARY PAUL D STEWART / SCIENCE PHOTO LIBRARY
Cephalopod (squid and allies) Spirula shell (spirula spirula) backlit and sectioned to show how the structure of partitions within the shell is reminiscent of the extinct ammonites and living nautiloids. Actually their closer relatives are the extinct belemites whose shell was represented by the chambered phragmocone. The shell, which is internall and hidden in the squid during life is a buoyancy organ in the shape of a planispiral. They live, bioluminesent, in the deep ocean between 100 to 1000 metres and have seldom been observed alive. Their shells are often washed up on shores in the tropical and subtropical waters of the Canary Islands and South Africa, but may be found as far away as new Zealand.
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