Cephalopods

The Intelligent Invertebrates

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Cephalopod Quick Facts Octopuses, squids, cuttlefish, and nautiluses are all

cephalopods.

Cephalopods are mollusks and are related to snails, slugs, clams, mussels, and oysters.

Cephalopods have lived in the Earth’s oceanic basins for more than 500 million years, and were dominant predators millions of years before fish appeared.

Nautiluses are the only cephalopod with external shells; squids and cuttlefish have internal shells; and octopuses have none at all.

Octopuses, squids, and cuttlefish have three hearts, and their blood is blue when exposed to air.

The nervous system of cephalopods is the most complex of the invertebrates and their brain is lo-cated in a capsule around their throats.

Octopuses have a toxin to neutralize their prey but only two types can kill humans with their toxin (some blue ring species and O. mototi).

REMEMBER

Prepared by Mike Mashburn, 2012

References Dr J.B. Wood’s Cephalopod Page: www.thecephalopodpage.org

The Octopus News Magazine Online: www.tonmo.com Laboratory of Robert Hanlon: www.mbl.edu/mrc/hanlon/

Unless otherwise noted all images in this publication were obtained from: http://commons.wikimedia.org

The second is the release of one or more com-pact, mucus-bound clouds close to the size of the cephalopod intended to confuse the preda-tor as to which is the real animal; this behavior may also be accompanied by the cephalopod changing color or “blanching.”

Cephalopods are fast-moving hunters that de-pend on vision to locate prey, detect predators, and communicate with one another. The cepha-lopod eye is probably the most sophisticated of all the inverte-brates and is as complex as the vertebrate eye; as such it is an often cited example of convergent evolution.

Like vertebrates, coleoid eyes contain an iris, pupil, and lens but not necessarily a cornea. Among coleoids squid have round pupils, while those of octopus are rectangular and the cuttlefish’s is W-shaped. The eyes of the nauti-loids are less sophisticated than other cephalo-pods; lacking a lens they have a small opening that acts like a “pin-hole” camera.

Somewhat paradoxically, the feature that makes the coleoids excellent visual communi-cators also makes them unchallenged masters of camouflage. They have the ability to rapidly and precisely vary the color, patterning and texture of their skin. This is possible through fine-motor control of projections on the skin called papillae, and pigment-containing and light-reflecting cells (chromatophores) located at, or directly under, the skin’s surface. This control is so precise that some squid have been observed “double signaling,” using half their body to communicate with an animal on that side while sending a completely different sig-nal to a receiver on the other side. 

Intelligence Cephalopods, and in particular octopuses, are generally considered to be the most intelligent of the invertebrates, but even so assessment of their intelligence remains controversial. What is clear is that cephalopods have the most complex brains of any invertebrate, enclosed in a carti-laginous brain capsule and surrounding the throat, it contains about 40 lobes and “up to” 300 million neurons (information processing nerve cells). However, cephalopod nervous sys-tems are not strongly centralized in the way that vertebrates’ are; for instance octopuses’ nervous systems have about 500 million neurons but two-thirds are located in the nerve cords of the arms and the arms exhibit significant autonomy even when disconnected from the brain.

Scientists studying octopuses have found indica-tions of intelligence in their ability to recognize shapes and patterns, to learn simple mazes, and to use landmarks for navigation while hunting. One study even appeared to document that octo-puses engage in play behavior when given an object to manipulate in an otherwise non-stimulating environment. In the wild octopuses have been observed to engage in planning and tool use in the collection, transport, and assem-bly of items like coconut and clam shells to cre-ate shelters.

Much work still needs to be accomplished to assess the degree and nature of cephalopod in-telligence, but it is apparent that these ancient and unique animals will continue to fascinate scientists and lay-persons alike for the foreseea-ble future.

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Phylum: Mollusca

Kingdom: Animalia Phylum: Mollusca Class: Cephalopoda Subclasses: Nautiloidea Ammonoidea Coleoidea

Scientific Classification

The Basics Cephalopods are exclusively marine animals represented by two extant subclasses, Nautiloi-dea and Coleoidea, and one extinct subclass, Ammonoidea. Extant subclasses contain about 800 species; Coleoidea includes the many spe-cies of octopus, squid, and cuttlefish; and Nau-tiloidea includes seven species of shelled Nau-tilus and Allonautilus.

Cephalopods are an an-cient class which appeared in the Earth’s ocean mil-lions of years before the bony fishes. The earliest cephalopods were primi-tive shelled nautiloids which evolved in the mid- to late-Cambrian period. Experiencing significant diversification during the Ordovician period, cepha-lopods became dominant in the Paleozoic and Mesozoic eras.

The fossil record contains about 17,000 species of cephalopods. Although their species’ diversity is greatly reduced in the modern era, cephalopods are currently found in all of the Earth’s oceanic basins from the tropics to the polar seas and occu-py all depths from the abyssal plain to the wave-swept intertidal zone.

As members of the phylum, Mollusca, the cepha-lopods are related to clams, mussels, slugs, snails and even worm-like, deep-sea Aplacophora. They share common molluscan anatomical features, although many of these are significantly modified and refined in cephalopods. A feature common to all mollusks is the mantle, the dorsal body wall which covers the visceral organs and often extends in the form of flaps. In cephalopods the mantle is quite muscular and serves as an organ of respiration and locomotion. Muscular contractions of the mantle cavity bring oxygenated water to the gills which can then be expelled with significant force through the funnel, giving the animals a sort of “jet propulsion.” The sudden burst of speed offered by “jetting” is use-ful in capturing prey or avoiding predators but is very energy intensive. So, most cephalopods rely primarily on their arms or fins for locomotion. The name cephalopod means “head foot” and in cephalopods the common molluscan “foot” has evolved into a number of appendages attached to the head and surrounding the mouth. Octopuses have four pairs of arms, while squid and cuttlefish typically have five pairs, with one pair, called ten-tacles, being elongated.

Anatomy

The arms of coleoids are generally equipped with suction cups along their entire length. The tentacles of squid and cuttlefish normally have suction cups only at the distal end, and in some squid these are accompanied by hooks. Nauti-loids have around 90 small appendages, re-ferred to as tentacles, which do not possess suckers but are sticky and partially retractable.

Cephalopods use their appendages to capture prey and maneuver it to their centrally-located mouth. All extant cephalopods have mouths equipped with a two-part beak, composed pri-marily of chitin, which they use to take bites of their prey as they hold it with their arms. Be-cause they are virtually indigestible, beaks are often the only identifiable cephalopod remains found in the stomachs of predatory species such as sperm whales.

Many mollusks have an external shell which shields their mantle, but among cephalo-pods only the nau-tiloids possess such a shell. In cole-oids the shell is internal, often greatly reduced and in some cases entirely absent. Notable examples of internal shells include the “ram’s horn shell” of Spirula spirula, the squid’s “pen,” and the cuttlefish’s cuttlebone, com-monly sold as a source of calcium for caged birds and reptiles. 

Cephalopods are the only mollusks to pos-sess a closed circulatory system. To carry oxygen in their blood cephalopods use cop-per-based hemocyanin, which makes their blood blue when exposed to air. Coleoids have paired branchial hearts that pump blood through their gills and a single systemic heart that transports blood to the other organs of the body. Each branchial heart is directly connected to a pericardial gland. The action of the branchial hearts is necessary for the production of primary urine in these glands via pressure filtration.

All coleoids, except for species of the subor-der Cirrina, are able to release clouds of ink to escape pursuit. The ink, primarily com-posed of melanin, is produced in a muscular sac which developed from the hind-gut and opens into the anus. Due to the ink sac’s proximity to the base of the funnel, ink can be dispersed by ejected water as the cephalo-pod uses their “jet propulsion.”

Two distinct uses of ink have been observed. The first is a simple release of a large, diffuse cloud of ink that serves as a “smokescreen” to obscure the predator’s view of the cepha-lopod while it jets rapidly away.

Colossal Squid Beak Mesonychoteuthis hamiltoni