CHAPTER XVI.
CEPHALOPODOUS MOLLUSCA.
"Monstrum horrendum, informe, ingens." Virgil.
The highest class of Molluscs is the Cephalopoda, which has been divided by Professor Owen into two Orders, Tetrabranchiata, or animals having four branchiæ, and the Dibranchiata, having two branchiæ. The first Family of the Tetrabranchiata, having the Ammonitidæ, contains the fossil Turrilites and Ammonites. The second Family, Orthoceratidæ, contains the fossil Gomphoceras and Orthoceras. The third Family, Nautilidæ, contains Nautilus.
The name Cephalopoda, as already stated, is taken from the position of the feet, which are inserted in the anterior part of the head: in Greek κεφαλὴ, head, and ποῦς-ποδὸς, foot.
The Cephalopodous Molluscs are indeed highly organised for Molluscs, for they possess in a high degree the sense of sight, hearing, and touch. They appear with the earlier animals which present themselves on the earth, and they are numerous even now, although they are far from playing the important part assigned to them in the early ages of organic life upon our planet. The Ammonites and Belemnites existed by thousands among the beings which peopled the seas during the secondary epoch in the history of the globe.
This great class is otherwise divided into two orders: Tentaculiferous Cephalopods, those furnished with strong fleshy tentacula, and Acetabuliferous, or sucker-bearing.
Tentaculiferous Cephalopods.