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CHAPTER XI
Squid,
Octopus and Cuttlefish
Class CEPHALOPODA
Subclass TETRABRANCHIA
This subclass, which includes the Chambered Nautilus and about 5000
species of fossil and extinct Ammonites, is not represented in American
waters. The living species of Nautilus from the Indo-Pacific are character-
ized by a large, chambered, external shell, by two. pairs of gills, and by their
numerous suckerless arms.
Subclass DIBRANCHIA
All of the living cephalopods with the exception of Nautilus belong to
this subclass which is characterized by animals that have one pair of gills, 8
or 10 arms which bear rows of suckers, and whose shell is internal or en-
tirely absent.
Order DECAPODA
(Spirula and Squid)
With 10 arms, 2 of which are the long tentacular arms; body long and
cylinder-shaped. An internal shell is present in most cases, and nmv be cal-
careous (the cuttlebone) or thin and horny (squid pen). The small suckers
on the arms are usually set on small stalks or peduncles and their apertures
are armed with horny rings or hooks.
Fajnily SPIRULIDAE
Genus Spirula Lamarck 1799
Spirula spirula Linne Common Spirula
Cape Cod to the West Indies. Worldwide.
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Figure 98