Marine Science Chapters

6.2.1

Abalone Introduction

Abalone are found worldwide. They are a unique type of snail, classified in the class Gastropoda of the phylum Mollusca. This is where all the snails are grouped. Abalone are in the family Haliotidae and the genus Haliotis. ‘Haliotis’ means ‘sea ear’ – which refers to the flattened shape of the abalone shell. The common name, abalone, is probably from the Spanish term aulon or aulone.


Abalone shell outside
Abalone shell, outside view, showing open holes and spiral (apex at top right of shell).

Abalone shells are unique snail shells, having a single, flat shell with a wide opening for the body and a single row of holes along one side of the shell(the left side). The holes continue to be formed throughout the life of the abalone. As they grow, new holes are made and older holes are filled in. These holes are used in the respiration, sanitation, and reproduction of the abalone. The typical spiral part of the snail shell is reduced and very flat in the abalone (called the apex). It may even be hard to notice this spiral in older animals who may have other organisms growing on the shell or have had a lot of abrasion in this area.


Abalone shell inside
Abalone shell, inside view, showing open holes, muscle scar (center), and apex (right, under shelf of shell).

Abalone are permanently attached to their shell in the center at a location called the muscle attachment. Some species produce a scar here and others do not. The shell begins in the larval form and abalone can only add to an existing shell after their larval stage. If they are removed from their shell, without injury, they can remain alive but cannot make a new shell – nor can they reattach to their old shell if it has been removed. Abalone rely on their shells for protection, so an animal without a shell would be easily eaten by a predator in nature. Inside the shell, the location under the spiral is called the apex just as it is on the outside of the shell. It is under a small, hard shelf at the end of the shell. A portion of the abalone body rests in the apex but there is no substantial attachment here.


Abalone foot
Abalone foot against an aquarium glass. The abalone is being held by its shell, pressing the foot against the glass. You can see the edge of the lobed epipodium and epipodial tentacles along the edge of the foot.

The foot of the abalone takes up most of the space inside the abalone shell. It is a broad and flat strong muscle. This is what attaches the abalone to the environment (usually a rocky surface) and is how it crawls around in search of food. This muscular foot is what is the prized food item by humans. The strength of this foot is renowned - they are exceptionally hard to remove from wherever they are attached. Abalone hunters usually bring special tools (abalone irons) to help remove them.


Abalone iron
Abalone iron used to 'pop' abalone from their substrate and remove them from their shells. This model was a new design, by Bob Evans (Force Fin designer), and easily doubles as an ice cream scoop.

Abalone irons help to remove the abalone from its substrate and are also designed so that they do not cut the abalone's sensitive skin. When an abalone is relaxed it usually has its shell up, off the substrate so that the abalone iron can quickly be inserted and 'pop' the animal off of its attachment. It the abalone is disturbed then it will clamp down on the substrate and the abalone iron is no help. The rounded edges of abalone irons protect the abalone from cuts because abalone will bleed to death if they are cut. Abalone hunters may or may not keep every abalone they pop off the substrate so they are careful not to cut any of their prey.


Abalone epipodium and epipodial tentacles
Abalone epipodium (lobed) and epipodial tentacles.

An epipodium is found along the edge of the abalone foot. This is a ‘ruffle’ of tissue with sensory tentacles. The color and texture of the epipodium, along with the color of the epipodial tentacles, is one way to distinguish between the different species of abalone. The epipodium and epipodial tentacles are often sticking out all around the edge of the abalone shell in an animal that has not been disturbed. When an abalone is disturbed it will pull in its epipodium and epipodial tentacles using its strong foot to clamp its shell down. When it has pulled down like this it is nearly impossible to remove a large abalone from a rocky surface in the ocean – they are so incredibly strong.


Edge of inside of abalone shell showing mantle, epipodial tentacles, epipodium and foot
Edge of inside of abalone shell showing mantle, epipodial tentacles, epipodium and foot.

Abalone mantle pushed aside by forceps
Abalone mantle pushed aside by forceps.

A thin mantle hangs from the edge of the muscle attachment over the body. This mantle is right next to the shell and the surface touching the shell has glands that secrete the shell material, continually adding layers to the shell. As the abalone grows it is the edge of the mantle that adds new shell to the outer rim of the shell (increasing the diameter of the shell) and new layers to the inside (increasing the thickness of the shell). If disturbed the mantle can shrink up next to the attachment of the muscle to the shell.


Abalone body removed from shell
Red abalone body removed from shell by carefully scraping the muscle attachment from the shell. A muscle scar is left on red abalone species in this area of muscle attachment.

Abalone organs identified
Abalone organs identified.

The organs of the abalone are in a circle surrounding the muscular foot. These are organs of the digestive, respiratory, circulatory and reproductive systems. The head and mouth of the abalone is right near the most recently formed open hole on the shell. The digestive tract bends to the left (when viewed from the top), back to the apex (under the spiral) where it turns and comes back along the left side ending in the anus. The anus is right under the last open hole and at the end of a slit in the mantle on the left side of the animal.


Abalone head with central mouth, flanked by a pair of oral tentacles and a pair of eyes
Abalone head with central mouth, flanked by a pair of oral tentacles and a pair of eyes.

Abalone heads have a mouth, pair of oral tentacles, pair of eyes, and an internal radula. The oral tentacles can be extended out, under the shell to sense the surrounding area. The eyes of the abalone are sensitive to light. The mouth of the abalone is pressed down on its food (algae) when feeding, and the radula is used to scrape pieces of the food. All abalone are herbivores, feeding primarily on various species of marine algae.


Abalone radula
Abalone radula from a four inch maricultured abalone. Note the brown area that is the area in use (stained by brown algae).

Abalone radula close up Abalone radula microscopic view
Abalone radula close up (left) showing rows of sharp teeth. Microscopic view of abaone radular teeth (right).

Abalone radula and odontophore
Abalone radula and odontophore. The odontophore is what presses the radula against the food while the animal is eating. It is made of cartilage.

The radula is like a mini chain saw with a constant sharpening mechanism. Radulae are a characteristic of many mollusks. These unique organs are flexible bands with rows of sharp hooked teeth. A hard material is located under the radula and is used to press the radular teeth against the food. As radular teeth become broken this outer area of the radula is shed and new (sharp) teeth are moved up. The mollusks continue to form new radular teeth their entire life. The part of the radula in the abalone that is used is often stained due to the pigments in their preferred algal food. The hard material used to press the radula in the abalone is called the odontophore and is a pair of cartilaginous-like structures operated by red muscle.


Abalone reproductive organ (greenish)
Abalone reproductive organ (greenish) is seen on the right side of the abalone . The foot and epipodium of the abalone is on the hand under the animal, it is stretching out so you can see the foot muscle and how it goes up and attaches to the center of the shell. The thin mantle is visible under the shell with the greenish reproductive organ in a pocket of the mantle. The animal is a female (males have a beige reproductive organ). The head of the animal is visible on the right just under the thumb with an eye raised up.

Abalone reproductive organs are on their right side. These are large, horned-shaped organs located on the side of the animal opposite from the open holes. The organ is located in a pocket of the mantle and gets larger and swollen just before spawning. Abalone females produce green eggs and their reproductive organ is a greenish color. Abalone males produce beige sperm and their reproductive organ is beige in color. Abalone never mate, they are all broadcast spawners. The eggs and sperm leave the reproductive organ and travel through a small duct to the area, near the anus, where they are released just under the open holes of the shell.


Abalone apex is at the back of the body, opposite the head
Abalone apex is at the back of the body, opposite the head. This is really just part of the body but it protrudes as a small knob that fits up under the spiral part of the shell. Below it is the heart with the clear abalone blood.

An apex is at the back of the abalone’s body. This is an area that may be composed of reproductive products as well as digesting algae. If the area is brown then it is the digesting algae. This lump of tissue rests just under the apex of the shell. Both the body area and the shell area are called ‘apex.’ When removing an animal with all of its body parts intact one needs to be a little careful to run a finger around the shelf of shell in this area to be sure not to tear the body apex.


Abalone heart
Abalone heart filled with clear blood. It contracts periodically to pump the blood to the animals tissues.

Abalone have clear blood, pumped by muscular contractions of the heart. Abalone have a rather simple circulatory system. The blood of the abalone circulates through the body and gills. In the body oxygen is taken from the blood by the cells and carbon dioxide given off from the cells to the blood. In the gills carbon dioxide is released from the blood to the water and oxygen is taken in from the water to the blood. Abalone are unable to clot their blood if they are cut. This means that if they get cut in nature or if an abalone diver accidentally cuts them they will bleed to death. Most abalone divers do not pluck an abalone from the rocks unless they are sure they will be taking it and they use a blunt abalone iron to remove the animal so as not to cut the abalone.


Abalone gills
Abalone gills are located right under the open holes of the shell.

Abalone gills are located just behind the head, on the left side of the body, where the holes in the shell are located. In this area there is a slit in the mantle that provides an opening directly under all the open holes in the shell. The body tissue in this area is covered with cilia that beat in a certain direction to create a constant water flow in, under the shell, by the head, then to the left side of the abalone over its gills, past the anus and out the open holes. This constant slow respiratory current not only provides clean oxygenated water for the gills of the abalone but it keeps this area clean by removing the wastes from the anus promptly. When abalone are reproducing their reproductive gametes (eggs or sperm) are released here as well and washed out through the holes in the shell by this respiratory current.


Abalone anus
Abalone anus is located at the far end of the slit in mantle (that exposes the gills).

The anus of the abalone is directly under the last open hole of the shell. Water circulating over the gills of the abalone leaves as a gentle upward current out of the open holes, taking with it the fecal material from the abalone.


Cleaning a shelled abalone at the beginning Cleaning a shelled abalone near the end
Cleaning a shelled abalone at the beginning (left). Cleaning a shelled abalone near the end (right) where the guts are only attached by a small area near the head.

The abalone’s organs are easily discarded, once the shell has been removed, by a tiny cut next to the muscle attachment. This reveals that the majority of the body of the abalone is its muscular foot and that this foot is solid muscle without any organs. All of the foot is edible. A v-shaped cut to remove the head (and radula) is all that is needed.


Abalone cleaned of its guts Abalone cleaned of its guts and epipodium
Abalone cleaned of its guts (left). Abalone cleaned of its guts and epipodium (right).

Most people prefer to remove the epipodium and bottom of the foot before preparing abalone. The traditional way is to trim the abalone to remove the epipodium and bottom foot layer then slice the muscle into ‘steaks.’ The steaks are very tough (like the heel of a shoe) at this point.


Sliced abalonesteaks before pounding Pounding an abalone steak
Sliced abalone steaks before pounding (left). Pounding an abalone steak (right).

Abalone steaks must be pounded to tenderize them. After pounding the abalone muscle gives up its toughness and the steak is then ready to be cooked. A traditional abalone steak is prepared by dusting the pounded abalone with flour or breadcrumbs and frying it quickly in oil or butter. Thirty seconds on each side is all that is necessary and the abalone steak is ready. The taste is similar to mild clam or chicken but has its own unique abalone flavor.


Floured abalone steak Cooking abalone steak
Floured abalone steaks before cooking (left). Cooking a traditional abalone steak (right).

Abalone steaks ready to eat Abalone ceviche
Abalone steaks ready to eat (left). Abalone ceviche (right).

Abalone can be prepared in many different ways. Traditional fried abalone steaks can be eaten plain or with a variety of condiments or sauces. Abalone can be served raw in ceviche (also called seviche or cebiche) by soaking the abalone overnight in lemon juice and adding vegetables to it in a marinade. Abalone chowder can be made in a similar fashion to clam chowder and often uses pieces of the epipodium as well as the bottom of the foot (all are edible). Today abalone is a delicacy, in the United States, often commanding 30 to 70 dollars a pound (for the trimmed, sliced and pounded steaks) before cooking.



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(Revised 12 November 2003)
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