Learning Resources for Teachers and Students
 | Basic and Detailed Anatomical Drawings of Cephalopods |
| Detailed Anatomical Drawings of Octopus |
| Detailed Anatomical Drawings of Cuttlefish (Sepia officinalis) |
| The Octopus and their Relatives- An introductory learning resource guide to Cephalopods |
Anatomy Drawings (On Line soon)
The Octopus and their Relatives-
An Introductory Learning Resource Guide to the Cephalopods.
This learning guide was developed by Helen Tozer, Aquatic Biologist, Steinhart Aquarium, San Francisco, who gratiously has allowed us to post this as a resource for teachers, students or any other cephalo-philes that might wish to use it.
Class Overview:
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Basic Anatomy and General Life History Notes
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Acknowledgements |
Summary
of the Class Cephalopoda
(or
what they all have in common)
1. Cephalopods are primarily designed to be open water hunters.
2. In the shelled cephalopods (Nautilus, Sepia and Spirula) the gas-filled chambers provide the animal with buoyancy.Changing the volume of fluid within the chambers regulates buoyancy.
3. Cephalopods swim by a water jet produced by the expulsion of water from the mantle cavity through the funnel.
4. Most living (extant) cephalopods contract the mantle wall to generate the water jet.They can do this because their shell is reduced and internal or lost completely, freeing the mantle wall for the pumping action.
5. Octopods have evolved a crawling benthic (bottom-dwelling) life-style.They use jet propulsion for long-distance swimming or escape.
6. Most cephalopods seize prey with a pair of prehensile tentacles and hold it with eight suckered arms.Octopus lack the pair of tentacles, Nautilus possess 38 non-suckered tentacles.
7. Prey is killed with a horny parrot-like beak and a pair of poison glands (modified salivary glands).The radula acts as a tongue.The digestive system is adapted to digest food rapidly.
8. Much of the anatomy and physiology of cephalopods is directly or indirectly related to their active life-style and high metabolic rate :
| Secondary folded gills |
| No gill cilia |
| Closed blood-vascular system |
| Accessory branchial hearts |
| Presence of hemocyanin |
| Highly developed eyes |
| Complex behavior and nervous system |
| Chromatophores |
| Ink glands |
In sexual reproduction the male uses a modified arm to transfer a spermatophore to the female.Before release, the eggs are fertilised in the oviduct or mantle cavity or in some cases from a spermatophore deposited by the male into a receptacle around the mouth of the female.The eggs are laid on substrate or scattered into the water.Development of the young is direct i.e. they hatch as miniature adults.
The Cephalopod Family Tree
Phylum : Mollusca
Class:Cephalopoda
| Subclass: Nautilodea– all possess an external shell, the living forms have slender,
suckerless tentacles, 2 pairs of gills and 2 sets of nephridia. All members of the class except for Nautilus
are extinct.
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| Subclass: Ammonoidea- all members of this subclass are extinct and known from the fossil record. | ||||||||||||||||||||||||||||
| Subclass: Coleoidea - shells are reduced, internal or absent. 8 to 10
appendages with suckers. One pair of gills and 1 pair of nephridia.
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Basic Anatomy and General Life History Notes
Please note that in the following paragraphs, words italicised are illustrated in the accompanying drawings which can be downloaded.
Molluscan
Diversity: Nautilus
The class Cephalopoda contains the squids, octopuses, nautiluses, and related
forms. The cephalopods have a highly developed head with large, well organized eyes.
The
chambered nautilus, because of its shell, is considered to be the most
primitive living cephalopod. The shell of the nautilus is partitioned
into chambers by the septa, which are made of the same material.
As the animal grows, it creates a new, larger chamber, and occupies only
the last largest body chamber in the shell.
The animal has a large number of tentacles (more than ninety!), topped by the leathery hood that is formed by two specially folded tentacles. The eyes of the nautilus, less well developed than the eyes of other cephalopods, lack a lens and operate somewhat like a pinhole camera.
The funnel,
located below the tentacles, is an evolutionary development of the
ancient molluscan foot. The sac-like body contains the viscera and the gill chamber
(not shown), which opens to the outside via the funnel. The tail-liked
structure protruding from the rear dorsal area is the siphuncle, a
continuous cord of special secretory tissue which penetrates the chamber walls,
or septa, through the siphuncle openings.
There are only six known species of Nautilus, and most live in the deep waters of the tropics. Consequently, relatively little is known about the biology of these animals. It is known, however, that the nautilus has developed three modes of movement. By day, the nautilus remains on the bottom of the ocean, either resting with its tentacles retracted or holding onto the bottom by use of its tentacles. Once free of the bottom, the nautilus swims by a kind of jet propulsion, like all cephalopod molluscs. Water is forced out of the mantle cavity through the funnel by a retraction of the body into the shell and a contraction of the funnel musculature, propelling the nautilus backward.
At night, the Nautilus
rises to shallower waters by increasing its buoyancy. To achieve this,
gas is secreted into the shell chambers through the siphuncle, and
water is removed from these chambers. This lessens the weight of the
nautilus, and it floats upward. Once in shallow waters, the nautilus swims to
reefs or rocky areas to feed. Here its tentacles are used for movement
and to capture slow-moving fish and invertebrate prey. When increasing light
signals the approach of day, the gas in the chambers is reabsorbed and
replaced by water, and the nautilus sinks back into its deep water retreat.
Molluscan Diversity: Squids and Octopuses
The squid and the octopus are two highly developed members of the class Cephalopoda. While the chambered nautilus relies for buoyancy on the ancestral molluscan shell, the squid’s thin shell is located within the mantle and is useful only for muscle attachment; the octopus has lost its shell entirely.
The squid swims by forcing water out the funnel, in a jet propulsion fashion. This, with its tapered, streamlined body and the broad triangular fins used for stabilization, makes the squid a highly effective swimmer. Normally, the squid swims backward. Squids may also swim forward, by directing the funnel posteriorly, and are capable of hovering motionless in the water. Over short distances, squid are among the most rapid moving of all marine organisms. Large squids can attain speeds of 24-32 kilometers (15-20 miles) per hour.
The muscular mantle of the squid and the mantle cavity it houses are strengthened internally by plates of cartilage in the body wall and by the remnants of the shell (called the pen, not shown). The eight arms and two tentacles can be held motionless in front of the squid’s head to aid in streamlining. The funnel is both moveable and muscular, so that in swimming, the opening (lumen) can be constricted, thereby increasing the pressure of the water forced out of it by the contraction of the mantle cavity.
Its swimming ability, coupled with its image-forming eyes, gives the squid a tremendous advantage as a predator. It can swim into a school of fish and quickly capture one with its long sucker-tipped tentacles. The fish is dispatched with a bite behind the head from the beak of the squid-accompanied by an injection poison. The beak is located in the center of the circle of arms, protruding from the mouth; it cuts the prey into small pieces that are then carried into the mouth by the radula (not shown).
Located on the arms are stalked, adhesive disc, or suckers (see circled enlargement), which in some species are reinforced by horny rings or hooks. Contraction when the suckers creates suction when the suckers come in contact with something solid. The tentacles, twice as long as the arms, have suckers only on their flattened ends.
The octopus does not normally swim about in the water. It will swim, however, if threatened. It swims with its soft bag-liked body held in the direction of movement, and its head and eight arms trailing behind. The funnel is directed rearward and the and the octopus moves in typical cephalopod fashion, propelled by forcing a jet of water out the funnel. The octopus lacks the streamlining that makes the squid such a successful swimmer; it prefers to remain in contact with a solid structure, pulling itself along using the suckers on its arms.
In most adult octopus species there are about 240 suckers on each arm, usually arranged in double rows. The suckers lack the stalk, the horny rims and the hooks possessed by the squid. Octopus suckers vary in size from a few millimeters to 7 centimeters in diameter. A sucker 2 centimeters in diameter requires a pull of six ounces to break its hold, so one can imagine the strength it would take to break a hold of two thousand suckers!
The octopus generally is a solitary dweller and seeks shelter or a permanent den in a cave or under rocks.
The Squid Dissection
There are two downloadable dissection drawings that go with this dissection guide. Everybody needs clean hands for this because we are going to eat the squid at the end of the class!
What you need:
2 paper plates 1 pair of dissection scissors 4 toothpicks
1 handlens 1 scrap of paper Squid diagrams
1-2 squid Pen or pencil
External anatomy:
Place the squid right side up on the plate. Look for the structures outlined below on your squid. So you don’t forget what everything is, mark down the structures on your diagram.
1.
Arms and tentacles.
Are they the same size? Do
they look alike? How many of each? Look at the suckers with the
handlens. Notice all the small
teeth in a ring around the suckers, they are used to holding fast to their prey.
Squid capture their prey with the tentacles and bring it in to the arms
to be held until the prey stops struggling.
2.
Beak. Look inside the
circle of the arms and tentacles. The
small black dot is the beak. Use
the toothpicks to push the tissue back from around it.
Can you see the 2 halves? It
looks like a parrot beak, and is very powerful.
It is used to tear pieces from the prey.
If you are careful you can use your fingers to gentle squeeze the beak
from the surrounding tissue (buccal mass). You might be able to see the radula,
which is the file-like tongue used to shred the pieces of food before they are
swallowed. When you remove the
buccal mass you may see a long tube attached to it.
This is the esophagus, the food passes
down the esophagus to the stomach at the other end.
3.
Eyes. Theses are much like our own, but the lens is shaped like a
football (ours is round). If you
carefully snip open the eye you can remove the hard lens with you fingers.
Squid can tell the difference between light and dark, blue and yellow and
forms a complete image of whatever it is looking at.
4.
The main part of the body containing all the organs is called the mantle.
The mantle is covered in pigment cells called chromatophores.
These cells are surrounded by muscle and are under nervous control.
The squid can change color rapidly and use this to camouflage themselves,
attract mates, and to communicate with each other.
5.
The squid has two fins, on the
mantle near the pointed end of its body. The
fins are used as stabilizers and to propel the squid with dainty motions at
relatively slow speeds and to guide sudden turns.
6.
The siphon is a short tube with
one opening near the eyes and the other end just under the mantle collar.
The siphon works to propel the squid through the water in the opposite
direction to which the siphon is pointing, much like jet propulsion.
To use this jet propulsion the squid takes in a large volume of water
through the large opening in the mantle and then closes off the opening. The
only way the water can escape is through the much smaller siphon. The mantle
muscles contract and the water comes out with enough force to propel the squid
through the water at about 20 miles per hour!
Internal Anatomy:
1.
Cut open the mantle of the squid directly down the midline
starting at the mantle opening called the collar,
next to the siphon and continuing down the length of the body to the tip.
Spread back the sides of the mantle to expose the internal organs.
2.
Is your squid male or female?
The gonads are located from near the tip
of the body to about the midpoint of the mantle.
In females, the ovaries containing the eggs are light yellow in color; they look and feel like Jell-O. Females also have a pair of egg shell glands called nidamental glands; they are the large, oval, white organs located at about the midpoint of the mantle cavity. Females also have an accessory nidamental gland located near the top of the main glands. They are close to the ink sac and pinkish in color, do not confuse them with the heart.
In males, the sperm is white in color and more watery than the eggs. The sperm pass through the small coiled tube called the vas deferens and into the spermatophoric gland which looks like a small sac with many intertwining circles within it. This gland adds substances to the sperm to make it into a sperm packet (spermatophore).
2. The stomach is an oval structure (sometimes difficult to find) about ½ inch long hooked to the side and near the top portion of the caecum. The caecum is located next to the gonads and both are about the same size and shape. The stomach is the major site for digestion and the caecum increases the surface area available for digestion.
3. The siphon can be pointed in different directions by the siphon retractor muscles. These muscles can be found up near the siphon and feel like strong tendons. These muscles are on each side of the diffuse, yellowish liver, which provides digestive enzymes to the stomach and caecum.
4. The ink sac is located on the rectum and looks much like a small silver fish or thin black line depending on how full the sac is. Very carefully, snip the sac at both ends and place it on the plate. Dip the tip of one of your cocktail sticks into the ink sac and try writing your name on the scrap paper. The ink is the pigment melanin which artists call sepia ink.
5. The gills are 2 white feathery structures found within the mantle cavity. At the base of each gill is a branchial heart (also called the gill heart) which pumps blood from the body up to the gills to be oxygenated. (These are the auricles). Each of these hearts is quite small and slightly yellowish in color. Squid actually have 3 hearts! The third heart is larger and located between the two branchial hearts. This is called the systemic heart and pumps oxygenated blood from the gills to the rest of the body. (This is the ventricle).
6. The squid is supported as it speeds through the water by a chitinous structure called a pen. This structure is the remnant shell. To locate the pen, lift up the head and place it down over the top of the organs of the body. Underneath where the head was lying on the plate, you will now notice a pointed area touching the plate right along the midline of the body. This is the tip of the pen. Grasp this tip and start to pull until the pen comes free of the mantle. The pen is as long as the length of the mantle and shaped like a transparent feather. You can dip this into the ink sac and right your name too!
1. Grasp the squid’s head in one hand and pull it down over the body towards the pointed end. This should pull most of the internal organs off in one piece. Remove the gills separately.
2. Now turn the mantle over and peel off all the colored skin. You should now be left with cleaned white mantle.
3. The arms and tentacles are also eaten and are cut off between the mouth area and the eyes keeping all of the tentacle-arms joined in one large ring. Discard all the internal organs.
4. Place the cleaned squid on the clean paper plate and take it down to “chef’s corner”.
5. Wash up ready to eat!
WOW!
Did you know that…?
(Or
cool facts on cephalopods to impress your friends with)
Nautilus:
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They are the most primitive living members of the cephalopods. |
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They are the only living cephalopods with large external shells. |
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Nautilus use jet propulsion to move around and adjust fluid levels in the chambers of their shells to change their buoyancy. |
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Nautilus has only been commonly seen in the last 20 years via exhibits in public aquaria. |
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There are 5 species still living (extant). |
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Their range is limited to the Pacific Ocean, where they are found at depths of approximately 300 to 1200 feet, at the base of steep reef faces. |
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Nautiluses have a huge daily migration moving from 1200 feet to 275 feet and back again. They withstand a temperature change of 30oF during their migration – at 1200 feet the temperature is about 40oF, at 275-300 feet the temperature is about 70oF. |
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They eat quite a varied diet from crustaceans such as small crabs and shrimp that they hunt, to dead fish from the reef which they scavenge. |
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They lay eggs with thick shells and attach them to the reef face. The Steinhart animals have laid eggs too, and we are presently trying to hatch and raise them. |
Squid:
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Squid are the most plentiful of all the cephalopods, often occurring in schools of many thousands. |
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Squid were known to Aristotle and were found in drawings as long as 4000 years ago. |
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They have been described in sailor’s yarns and legends as sea monsters or the ”Kraken”. |
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In “20,000 Leagues Under The Sea”, by Jules Verne the submarine The Nautilus was attacked by a giant squid. |
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The largest living cephalopod is the Giant Squid (Architeuthis). They have been found washed up on beaches and in the stomachs of Sperm whales, but have never been seen alive. In 1933 one washed up on a beach in New Zealand that was over 69 feet long with eyes 16 inches in diameter! That was probably a small one. These squid live at depths of 1000 to 3000 feet. |
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The most ferocious squid is probably the Humboldt Squid which lives off the coast of South America and reaches a length of 12 feet and weighs about 300 lbs. They travel in schools and attack their prey en masse. They have even attacked scuba divers. |
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Squid are all pelagic i.e.; they spend their lives in the water column. |
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They are the fastest of all invertebrates, moving at speeds of up to 20 m.p.h. When they swim they go backwards. |
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Squid can probably see finer detail than us and can distinguish polarized light. |
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They can communicate with each other using sign language and rapid color changes. Their “language” consists of many thousands of combined color variations and patterns, humans with an extensive vocabulary use only about 2000 words! |
Cuttlefish:
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Cuttlefish like their squid cousins spend most of their time in the water column. |
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They are commonly found around the European coasts and off the coast of Japan. |
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They have an internal reduced shell that is quite dense and helps to stabilize the animal as it swims. It is called the cuttlebone and is often sold in pet stores as a treat for birds. |
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Cuttlefish tentacles can shoot out over 1½ feet to catch their prey. |
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Cuttlefish range in size from 1 to 12 inches. (Except for Sepia apama an Australian species which reaches 3 feet in length!) |
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Like octopus, cuttlefish can change the texture of their skin to blend in with their surroundings. |
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Researchers have identified over 50 color patterns or “words” that cuttlefish commonly use to communicate with each other. |
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Cuttlefish are often cannibals especially around mating season. |
Octopus:
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Octopuses are the most intelligent of all cephalopods. They have some ability to learn and devise solutions to simple problems. |
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They range in size from ½ inch in diameter (Californian Octopus) up to 20 feet across (Giant Pacific Octopus). |
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All octopods are venomous, they capture prey with their arms, bringing it up to the webbed area where the arms join the mantle, and bite it with their powerful beaks, injecting a neurotoxic venom into the bite. The venom varies in potency from species to species. The most powerful venom found in octopods so far is that of the Blue-ringed Octopuses (Hapalochlaena spp.). Some of which can kill a human in a few minutes. |
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Most species of octopus are benthic i.e., bottom dwelling. They crawl along the ocean floor using their sensitive arms and suckers to find food. Often octopus will locate and capture prey, paralyze it with their venom, tuck it up inside their arms and carry it back to a den to consume it in privacy and comfort. |
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Dens are also used by the females of many species to brood their eggs. They deposit them on the roof or sidewalls of the den where they can guard and care for them. Usually about the time the eggs are due to hatch, the female will die, having starved herself to death to care for her eggs. |
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Octopuses in captivity are incredible Houdini’s. Even the Giant Pacific Octopuses can escape from through incredibly tiny holes. This is because they have no bones or shell to make them rigid. The only solid part of their bodies is the beak. If a hole is small enough for the beak to fit through than the rest of the animal can follow! |
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Octopus suckers are incredibly sensitive functioning as a nose and fingertips! They are very delicately controlled and each sucker can be moved individually, no wonder octopuses have such large brains. In large species such as the Giant Pacific Octopus, each arm can have up to 280 suckers. |
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Just for kicks below is a glossary of the word octopus in a few different languages! |
French = pulpe
Spanish = pulpo
German = Tintenfisch
Czech = chobotnice (pronounced KHO-boat-neats-eh)
Slovene = hobotnica
Classical Greek = polypous (paw-LOOP-oos)
Japanese = tako: yudedako (boiled octopus)
Finnish = meritursas, tursas; mustekala (also means cuttlefish
and squid)
Hungarian = polip
Swahili = pweza mkubwa.
Useful Information Sources:
Internet:
Cephalopods at the National Museum of Natural History
Incredible Suckers by The Nature Series/BBC ISBN EBC0107
Acknowledgements:
Harper & Row publishers – for allowing us to use excerpts from The Marine Biology Coloring Book.