INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM MULTICELLULAR ANIMALS (METAZOA)

SUBKINGDOM EUMETAZOA

SECTION TRIPLOBLASTICA, OR BILATERIA

SUBSECTION SPIRALIA

PHYLUM MOLLUSCA

CLASS CEPHALOPODA

SUBCLASS NAUTILOIDEA

Nautiloids are a group of cephaloids characterized by an external multichambered shell, two pairs of gills, four atria, four Kidneys, and A large number of tentacles lacking suckers. The Nervous system is arch-like and nonganglionated, and the eyes are of simple Structure.

In the modern cephalopod fauna, the subclass is represented by a single genus, Nautilus, comprising six species, although numerous genera and species of extinct nautiloids are known. The best-known species, Nautilus pompilius (Fig. 245, a), inhabits the tropical Regions of the Indian and Pacific Oceans.

Nautiluses are slow-moving animals that inhabit primarily the Water Column at depths down to 500–700 m, though they can also ascend to surface layers. They hunt at night for small crustaceans and other sluggish prey, but also readily scavenge. For reproduction, they aggregate in the shallow waters of coral islands, where females lay very large eggs (up to 4 cm), attaching them singly to submerged objects. The eggs hatch into miniature nautiluses with a well-developed shell already possessing several chambers. The shell grows along its free margin by forming new chambers, into which the mollusk's body successively moves.