"The Paper-nautilus, or Argonaut, [floats] gracefully on the surface of the sea, trimming its tiny sail to the breeze, just sufficient to ruffle the surface of the waves, it looks like an exquisite living shallop."

Argonauto Argo (Linnaeus)

"The Paper-nautilus, or Argonaut, [floats] gracefully on the surface of the sea, trimming its tiny sail…

"The argonaut can blush, turn pale, and show through its transparent shell its body changing in sudden shades."

Argonauta Papyracea in its Shell

"The argonaut can blush, turn pale, and show through its transparent shell its body changing in sudden…

"The principal apparatus of progression of the animal is the funnel with which it is furnished, in common with all Cephalopods, and which is very long in the argonaut. Aided by this apparatus, it ejects water after it has served the purpose of respiration, and in doing so, projects itself through the water."

Argonauta Papyracea Swimming

"The principal apparatus of progression of the animal is the funnel with which it is furnished, in common…

"In one genera [of the <em>Octopodidae</em> family] the arms are completely united in their whole extent by a thin membrane."

Cirrhoteuthis Mulleri (Eschricht)

"In one genera [of the Octopodidae family] the arms are completely united in their whole extent…

Compound coral head with polyps partly expanded and partly contracted. The expanded polyps show the tentacles which surround the mouth; the contracted polyps show the polygonal outline from crowding.

Coral Head

Compound coral head with polyps partly expanded and partly contracted. The expanded polyps show the…

A compound coral head with crowded prismatic corallites. The specimen represents a worn pebble, formerly a part of a larger head.

Coral Head

A compound coral head with crowded prismatic corallites. The specimen represents a worn pebble, formerly…

"Hydractina Echinata. c, the canosarc, forming an incrustation over the object on which it lives; n, nutritive polyps; r, reproductive polyps, bearing buds in which are ova; t, tentacles." &mdash; Galloway

Hydractina Echinata

"Hydractina Echinata. c, the canosarc, forming an incrustation over the object on which it lives; n,…

"Side view of <em>Amphioxus</em>: fs, fin supports; nc, notochord; ot, oral tentacles."&mdash;Finley, 1917

Side view of lancelet

"Side view of Amphioxus: fs, fin supports; nc, notochord; ot, oral tentacles."—Finley,…

Chambered nautilus, showing chambers with soft body in outer chamber. It is closely related to the squids and cuttlefishes, but has the body enclosed in a flat-spiral shell.

Nautilus

Chambered nautilus, showing chambers with soft body in outer chamber. It is closely related to the squids…

As the name indicates, the octopus has eight arms instead of ten, as in the squids and cuttles.

Octopus

As the name indicates, the octopus has eight arms instead of ten, as in the squids and cuttles.

"The Devil-fish (Octopus). A, at rest; B, swimming. a, arms, with suckers on the inner aspect; e, eye; s, siphon or funnel." -Galloway, 1915

Octopus

"The Devil-fish (Octopus). A, at rest; B, swimming. a, arms, with suckers on the inner aspect; e, eye;…

"A very ugly-looking creature, which belongs to the <em>Octopodidae</em> family, is the Octopus."

Octopus Brevipes (d'Orbigny)

"A very ugly-looking creature, which belongs to the Octopodidae family, is the Octopus."

"A very ugly-looking creature, which belongs to the <em>Octopodidae</em> family, is the Octopus."

Octopus Horridus (d'Orbigny)

"A very ugly-looking creature, which belongs to the Octopodidae family, is the Octopus."

"A very ugly-looking creature, which belongs to the <em>Octopodidae</em> family, is the Octopus."

Octopus Macropus (Risso)

"A very ugly-looking creature, which belongs to the Octopodidae family, is the Octopus."

"A very ugly-looking creature, which belongs to the <em>Octopodidae</em> family, is the Octopus."

Octopus Vulgaris (Lamarck)

"A very ugly-looking creature, which belongs to the Octopodidae family, is the Octopus."

This creature, belonging to the <em>Octopodidae</em> family, "changes its color under any exertion, so that the animal at rest and in motion are two different beings."

Pinnoctopus Cordiiformis (Q. & G.)

This creature, belonging to the Octopodidae family, "changes its color under any exertion,…

Vertical section through a polyp. Mouth surrounded by tentacles and beneath it the "stomatodaeum."

Vertical Section Through a Polyp

Vertical section through a polyp. Mouth surrounded by tentacles and beneath it the "stomatodaeum."

The squid is the best example of the cephalopod group. It is abundant along the Atlantic coast. Squids swim in schools and feed on young herring and mackerel.

Squid

The squid is the best example of the cephalopod group. It is abundant along the Atlantic coast. Squids…

"Diagrammtic longitudinal section of an Anthozoan zooid. m, Mesentery; t, Tentacles; st, Stomodaeum; sc, Sulcus; r, Rotteken's muscle; s, stoma; lm, Longitudinal muscle; d, diagonal muscle; go, gonads." &mdash;Encyclopedia Britannica, 1910

Anthozoan Zooid

"Diagrammtic longitudinal section of an Anthozoan zooid. m, Mesentery; t, Tentacles; st, Stomodaeum;…