Castro−Huber: Marine Biology, Fourth EditionII. Life in the Marine Environment7. Marine Animals without a Backbone
© The McGraw−Hill Companies, 2003
Squids (
Loligo;
Fig. 7.25
b
) are bet-ter adapted for swimming than are oc-topuses. The body is elongate andcovered by the mantle, which also,forms two triangular fins. Squids can re-main motionless in one place or movebackward or forward just by changingthe direction of the siphon. Eight armsand two tentacles, all with suckers, cir-cle the mouth. The tentacles are longand retractable and have suckers only atthe broadened tips. They can be swiftly shot out to catch prey. The shell is re-duced to a chitinous
pen
that is embed-ded in the upper surface of the mantle. Adult size varies from tiny individualsof a few centimeters in length to 20 m(66 ft) in the giant squid (
Architeuthis
),the largest living invertebrate. The giantsquid is a deep-water species knownmostly from specimens that have been washed ashore or found in the stomachs