Invertebrate Anatomy OnLine

Busycon carica

and Buccinum undatum ©



Copyright 2003 by

Richard Fox

Lander University


            This is one of many exercises available from Invertebrate Anatomy OnLine , an Internet laboratory manual for courses in Invertebrate Zoology.   Additional exercises can be accessed by clicking on the links on the left.   A glossary and chapters on supplies and laboratory techniques are also available.   Terminology and phylogeny used in these exercises correspond to usage in the Invertebrate Zoology textbook by Ruppert, Fox, and Barnes (2004).   Hyphenated figure callouts refer to figures in the textbook.   Callouts that are not hyphenated refer to figures embedded in the exercise. The glossary includes terms from this textbook as well as the laboratory exercises.  


Mollusca P, Eumollusca, Conchifera, Ganglionura, Rhacopoda, Gastropoda C, Prosobranchia sC, Caenogastropoda O, Neogastropoda sO, Muricoidea SF, Melongenidae F and Buccinidae F(Fig 12-125)

Mollusca P

            Mollusca, the second largest metazoan taxon, consists of Aplacophora, Polyplacophora, Monoplacophora, Gastropoda, Cephalopoda, Bivalvia, and Scaphopoda.   The typical mollusc has a calcareous shell, muscular foot, head with mouth and sense organs, and a visceral mass containing most of the gut, the heart, gonads, and kidney.   Dorsally the body wall is the mantle and a fold of this body wall forms and encloses that all important molluscan chamber, the mantle cavity. The mantle cavity is filled with water or air and in it are located the gill(s), anus, nephridiopore(s) and gonopore(s).   The coelom is reduced to small spaces including the pericardial cavity containing the heart and the gonocoel containing the gonad.

            The well-developed hemal system consists of the heart and vessels leading to a spacious hemocoel in which most of the viscera are located.   The kidneys are large metanephridia.   The central nervous system is cephalized and tetraneurous.   There is a tendency to concentrate ganglia in the circumenteric nerve ring from which arise four major longitudinal nerve cords.

            Molluscs may be either gonochoric or hermaphroditic.   Spiral cleavage produces a veliger larva in many taxa unless it is suppressed in favor of direct development or another larva.  Molluscs arose in the sea and most remain there but molluscs have also colonized freshwater and terrestrial habitats.


            Eumollusca, the sister taxon of Aplacophora, includes all molluscs other than aplacophorans.   The eumolluscan gut has digestive ceca which are lacking in aplacophorans, the gut is coiled, and a complex radular musculature is present.


       Conchifera, the sister taxon of Polyplacophora, includes all Recent molluscs other than aplacophorans and chitons. The conchiferan shell consists of an outer proteinaceous periostracum underlain by calcareous layers and is a single piece (although in some it may appear to be divided into two valves). The mantle margins are divided into three folds.


            Most Recent molluscs are ganglioneurans, only the small taxa Aplacophora, Polyplacophora, and Monoplacophora are excluded. Neuron cell bodies are localized in ganglia.


            The mantle cavity is posterior in the ancestor although it may be secondarily moved to an anterior position by torsion. This taxon includes gastropods and cephalopods.

Gastropoda C

            Gastropoda is the largest molluscan taxon and is the sister group of Cephalopoda. Gastropods are united by descent from a torted ancestor although many exhibit various degrees of detorsion.   Many are coiled and asymmetrical but the ancestor was probably symmetrical.   Gastropods are relatively unspecialized molluscs known collectively as snails.   The univalve shell, present in the ancestral gastropod and in the majority of Recent species, is reduced or lost in many representatives.   The flat creeping foot was inherited from their eumolluscan ancestors but gastropods have developed a distinct head with an abundance of sophisticated sense organs. The originally posterior mantle cavity has become anterior as a consequence of torsion, although detorsion has reversed this condition in many.   Gastropods were originally gonochoric and most remain so but many derived taxa are hermaphroditic.   Most are marine but many taxa have invaded freshwater and the only terrestrial molluscs are gastropods.   Most have a single gill, atrium, and nephridium but the most primitive representatives have two of each.    Only one gonad, the right, is present. The ancestor probably had an operculum.   The nervous system is streptoneurous (twisted by torsion).

Prosobranchia sC

     Prosobranchia was once one of three great gastropod subclasses but it is no longer considered to be a monophyletic taxon, although the concept continues to be used as a pedagogical convenience. Prosobranchs are the gastropods most like the ancestral snails.   They are torted and most have a shell and are coiled and asymmetrical. The mantle cavity is anterior.   Most are gonochoric and most have an operculum.   Most have only one gill in the mantle cavity but some primitive taxa have two. The right atrium is lost in most. Prosobranchs are specialized for life in marine benthic habitats although representatives are also found in freshwater and on land.

Caenogastropoda O

                Caenogastropoda includes the two large and successful groups, mesogastropods and Neogastropoda. One gill, one nephridium, and one atrium are present.   The gill is monopectinate, with filaments on only one side of the central axis.   This new gill is less prone to fouling with sediment and silt and is probably largely responsible for the success of these snails as it allowed invasion of soft-bottom habitats.  

Neogastropoda sO

     Neogastropods are the modern marine snails.   They have a well-developed, gill-like, bipectinate osphradium in contrast with the much simpler osphradium of mesogastropods. The rachiglossate radula has three teeth in each transverse row whereas that of mesogastropods has seven.   A gland and valve of Leiblein are present in the gut. Most are carnivores and all are marine. Neogastropoda includes many well-known gastropods such as the tulip snails, whelks, conchs, oyster drills, mud snails, olive snails, and cones.

Laboratory Specimens

            Busycon whelks are all large (22 cm) snails and are suitable subjects for the laboratory study of prosobranch anatomy although smaller species are more convenient.   Busycon species are found in shallow water along the east coast of North America from Massachusetts south to the Gulf of Mexico.   Most species are dextral.  

           These dissection instructions are written for the knobbed whelk, Busycon carica, which is a dextral (right handed) species.   If a sinistral species, such as Busycon contrarium, is dissected, then right-left spatial relationships will be reversed.

          Many species could be substituted for Busycon if desired.   Virtually any snail in Muricoidea can be used with this exercise.   The most likely alternative is Buccinum undatum(Buccinidae) and parenthetical notes indicate points in which these snails differ from Busycon.

            Buccinum undatum, the northern whelk, is a common snail of moderate size (8 cm) on the northeastern coast of North America and in northern Europe (Fig 12-46A).   Several other species occur in the Pacific northwest.  Buccinum undatum is commercially harvested for human consumption in Europe.  

            Other alternatives are Neptunea (neptune) in the northeast and northwest, Melongena corona (crown conch) in Florida and the Gulf of Mexico, Fasciolaria (tulip snail) in the southeast and Caribbean, and Thais(rock snail).   All are of moderate to large size and have similar anatomical features.   Similar, but smaller, snails in Nassariidae (Ilyanassa) and Muricidae (Nucella) may also be used.   A dissection guide for Ilyanassa obsoleta is available at by clicking on the link on the left .

            The exercise includes study of external and internal anatomy but some instructors may wish to shorten and simplify the experience by omitting the internal anatomy portion.   Much of gastropod anatomy is visible after the snail is extracted from the shell and its mantle cavity opened without further dissection.

            The instructions are written for living, relaxed specimens but can be used with preserved material as well.   Living specimens are far superior to preserved.   The colors of organs in living and preserved specimens are likely to differ and indications of color apply to living specimens unless otherwise noted. The Busycon dissection does not require a dissecting microscope.   


  Anesthetization and Relaxation

            Snails are notoriously difficult to anesthetize.   Upon detecting anesthetic in their environment, they immediately withdraw, close the operculum, and isolate themselves from the anesthetic.   Relaxation is important, however, as contracted animals are difficult to remove from their shells and difficult to dissect after removal. Special gradual relaxation techniques must be employed with most molluscs.

            Specimens should be relaxed by the teaching staff prior to the laboratory meeting. The snails should be placed in a container of seawater about 24-36 (36 hours for large specimens) hours before needed. The animals should be just covered by seawater so that the volume of seawater in minimized. Concentrated magnesium chloride (70 parts per thousand) is added dropwise to the seawater containing the animals.   Arrange a slow siphon or drip-string to drip 70 ‰ magnesium chloride slowly into the container.   Avoid disturbing the animals until it is time to use them. Animals disturbed during the process will often contract into the shell and refuse to re-extend.   Specimens should be completely relaxed and incapable of contraction.

External Anatomy

            The snail body consists of an anterior head, ventral foot, and posterior/dorsal visceral mass.   The visceral mass is coiled and extends deep into the furthest recesses of the secreted, external, calcareous shell.   The head and foot are bilaterally symmetrical.   The shell and visceral mass are asymmetrical and coiled.


     The shell of Busycon carica, the knobbed whelk, is heavy and ornamented with strong, blunt knobs, or spines, around the shoulders of the larger whorls (Fig 1).   (The sculpture of Buccinumconsists of low, rounded, longitudinal ridges.)   The shell is dextral and in Busycon may reach lengths of 22 cm.   (Buccinum reaches 8 cm.)

            The shell consists of a series of whorls wound around a hidden central axis, the columella (Fig 1, 12-27A,B).   The last whorl, called the body whorl, is the largest and contains the head, foot, much of the visceral mass, and the mantle cavity.   It opens to the exterior by the large aperture.   The smaller whorls stacked atop the body whorl contain the upper regions of visceral mass.   Together they form the spire.   The aperture is elongated anteriorly to form a siphonal canal (if long, as in Busycon), or siphonal notch (if short), in which the siphon is housed.  

            Most snails, Busycon carica and Buccinum included, are dextral, or right handed. If the shell is held upright, with the spire up and the aperture facing the observer, then the aperture is on the right side (Fig 1, 12-27A,B).   The opposite, much less common, condition is sinistral, in which the aperture is on the left of the central axis.   Busycon contrarium, the left-handed whelk, is one of the few sinistral snails.  

            The shell grows through the addition of new material around the edge of the aperture.   The body whorl is the youngest part of the shell.   The tiny whorl atop the spire is the oldest.   The protoconch, or the shell of the veliger larva, is originally located at the top of the spire but is delicate and does not persist into adulthood.

            The shell consists of an outer periostracum made of the protein conchiolin.   It is thin and inconspicuous in most species of Busycon and Buccinum (but is very thick and obvious inBusycon canaliculatum).   Under the periostracum is a layer of prismatic calcium carbonate followed by an innermost layer of lamellar, or nacreous calcium carbonate.  

Figure 1.   The shell of a knobbed whelk, Busycon carica, from Beaufort, North Carolina. A hole has been chiseled in the body whorl to reveal the columella and the attachment scar of the columellar muscle. Gastrop158L.gif

Figure 1

            The periostracum and prismatic layers are secreted by the free anterior edge of the mantle (mantle skirt) but the inner lamellar layers, which are in contact with the surface of the body, are secreted by the epidermis of that surface (mantle).


"     A snail is attached to its shell by a single columellar muscle that runs from the foot to an insertion high on the columella of the shell (Fig 1). This is the muscle used by the animal to withdraw its head and foot into the shell.   The columellar muscle is homologous to an ancestral pedal retractor muscle but only the right columellar muscle is present in adult snails.   The insertion is deep within the shell and is not visible or accessible in an intact snail. To remove the animal from the shell it is necessary that you separate the columellar muscle from the columella and then unwind the snail out of its shell but first you must gain access to the muscle.

            For large snails with heavy shells, like Busycon, a window must be chiseled in the shell to gain access to the muscle.   In smaller species with lighter shells the entire shell can be cracked and pieces.  

            For Busycon, orient the shell so its aperture is facing you and the spire is up (Fig 1).   Using a hammer, cold chisel, and safety glasses, chop a window high on the side of the body whorl immediately to the left of the top of the aperture.   Do not damage the soft tissues within.  

            With a scalpel, or a blunt probe, reach into the window and separate the glistening white columellar muscle from the shell.   Do this by scraping the muscle away from the shell.   Most of the muscle is best reached from above the body but you may have to cut some of the fibers from below the body as well.   Do not cut the body of the snail.   When you think you have detached all the muscle, exert a steady but gentle pull on the operculum and/or foot.   The animal should uncoil from the whorls of the shell and slide smoothly out of the aperture but DO NOT FORCE IT.   If it does not come out easily, look for parts of the muscle that you neglected to cut, sever them, and try again.   If you use force to remove the animal, the delicate visceral mass will tear apart.  Should this happen your study of snail anatomy will be made more difficult.  

            Buccinum and other small or thin-shelled species are best extracted by cracking the shell with a vise or C-clamp and then removing the shell carefully and in pieces from around the animal.   Place the snail in the vise and apply pressure around the aperture until the shell cracks.   You can hear and feel it crack.   Remove the shell from the vise and see if any pieces of it can be removed without damage to the soft anatomy.   If so, remove and discard them.   Put the shell back in the vise and apply pressure to an uncracked portion of the shell until it cracks.   Remove any loose pieces of shell as before.

            Never close the vise on soft parts or apply additional pressure after the shell cracks.   Pressure should be applied only to sound, uncracked parts of the shell.)

            Continue removing shell in this fashion until you have worked your way from the aperture to the insertion of the columellar muscle.   Use a scalpel to scrape the columellar muscle away from the columella. When you think you have detached all the muscle, exert a steady but gentle pull on the operculum and/or foot.   The visceral mass should uncoil from the whorls of the shell and slide smoothly out of the aperture but DO NOT FORCE IT.   If it does not come out easily, look for intact parts of the muscle you overlooked, detach or sever them, and try again.   Never use force to remove the animal as the visceral mass is delicate and will tear apart.   Should this happen your dissection will be made more difficult.


            Study the extracted and relaxed animal in a dissecting pan of isotonic magnesium chloride (if living) or tapwater if (preserved).   First find the large, tough, muscular foot, to which is attached the flat, brown, horny (proteinaceous) operculum (Fig 2, 12-45A).   The operculum is a door used to close the aperture when the head and foot are withdrawn into the shell (Fig 12-27C-F). The foot and operculum are ventral.   The sole of the foot is white but its sides are dark.   (The sole of the foot of Buccinum is brownish and its sides are mottled black and white.)   

            Find the white columellar muscle on the right, ventral side.   It arises from the posterior end of the foot (but not from the sole) and passes posteriorly.   The ventral skirt of the mantle margin passes over it.   This is the right columellar muscle.   There is no left.   Distinguish between the dark ventral foot and the lighter dorsal visceral mass.  


            Look at the end of the foot opposite the operculum to find the small head sitting atop the anterior end of the foot.   The head is dorsal and anterior.   Note that the head and foot are bilaterally symmetrical. The head bears two triangular, cephalic tentacles on its anterolateral margins (Fig 2).   Each tentacle bears a small dark eye on its lateral edge about 1/3 - 1/2 of the way back from the tip (Fig 2).  

            Orient the animal.   The foot is ventral, the head anterior, and the visceral mass dorsal.   Be sure you can recognize anterior, posterior, dorsal, ventral, right, and left before you continue.

Figure 2.   En face view of a male Buccinum undatum.   Redrawn from Cox (1960). Gastrop159La.gif

Figure 2

            Your specimen may, or may not, have a long, tubular, retractile proboscis extending from between the tentacles on the anterior-ventral surface of the head (Fig 2, 4, 12-45A).   The proboscis is eversible but is normally kept retracted inside the head (Fig 12-44).   If it is retracted, you will not see it now but will see instead a slit-shaped proboscis pore through which the proboscis can be everted.   The proboscis pore is located on the midline of the ventral surface of the head.   Sometimes snails evert the proboscis as they relax and the proboscis may be extended in your specimens.    

Examine the proboscis if it is everted.   The mouth is located at the tip of the proboscis (Fig 2, 12-45A).   If the proboscis is not everted, reach into the proboscis pore with a forceps, grasp the proboscis, and pull it gently out of the pore.   If it does not come readily, do not force it.   The animal must be fully relaxed or you will not be able to evert it.   If you were successful, find the mouthat the tip of the proboscis.  

            Look at the right side of the head for a long, tapered, straplike penis beside the right tentacle (Fig 2, 12-45D).   If it is present, your specimen is a male.  

Visceral Mass

            Look now at the posterior dorsal part of the body.   The soft, mostly brownish or greenish, posterior end of the animal is the visceral mass (Figs 3, 4, 12-45B).   It is coiled and asymmetric. The greenish brown tissue is the digestive cecum (Figs 3, 4, 12-45).   The dorsal epithelium of the visceral mass is the mantle.   The anterior half of its dorsal surface is covered by the mantle cavity just posterior to the head. The mantle cavity is a deep pocket formed by a fold of the mantle.

Figure 3.   View of the left side of a female Buccinum undatum drawn as if with a transparent shell.   Redrawn from Cox (1960).   Gastrop160La.gif

Figure 3

            Note that the visceral mass is coiled and consists of several whorls.   The visceral mass is the coiled portion of the body that sits dorsal to the foot and extends up unto the highest, smallest whorls of the spire.

            Most of the visceral mass is occupied by the dark, greenish, brownish, or black, lobulated digestive cecum.   Near the apex, however, there is a gonad (Figs 3, 4, 12-45C,D), usually of contrasting color, embedded in the tissue of the digestive cecum and visible on the surface.

            >1a. Snails are frequently parasitized by larval stages of trematode flatworms (flukes).   Look through the thin body wall into the visceral mass for short, worm-like, rod-shapedsporocysts or rediae which may be present (Fig 10-35).   If you find some, make a small break in the body wall and remove a few larvae to a microscope slide.   Make a wet mount and examine them with the compound microscope.   Note the next generation of larvae (clonally produced) inside the redia.   These are cercariae.   Try to rupture one of the rediae and release the cercariae contained inside.   Each of these cercariae is capable of infecting another host. <

            On the right dorsal side of the visceral mass, between the base of the visceral mass and the posterior end of the mantle cavity, is the large, pale brown nephridium (or kidney) (Fig 4, 12-14B, 12-45C) .   It is homologous to the left nephridium of the ancestral gastropod, even though it is on the right.   It is divided into two parts, both of which are clearly visible through the body wall.

Figure 4.   Dorsal view of a male Buccinum undatum.   The mantle cavity has been opened with a mid-dorsal incision through the hypobranchial gland.   Redrawn from Cox (1960). Gastrop161La.gif

Figure 4

            On the dorsal surface of the visceral mass look for a small, translucent, pinkish area between the kidney and the posterior end of the gill.   (It is creamy-white in Buccinum and on the left.)  This is the heart in the pericardial cavity surrounded by the membranous pericardium (Fig 4, 12-45B).              

            Embedded in the dorsal surface of the digestive cecum is the translucent, elongated stomach with a conspicuous, branching, white artery coursing over its surface (Fig 12-45B,C).  (Only a little of the stomach is visible in Buccinum.   It is pale and on the left, posterior to the nephridium.)

            In reproductive females, a large, creamy-white egg capsule gland (or nidamental gland, or shell gland) can be seen through the body wall just anterior to the kidney on the right side (Fig 12-45C,12-56A).   It occupies most of the anterior lateral wall of the visceral mass ventral to the mantle cavity.


            In molluscs the dorsal and lateral body wall is known as the mantle.   A large fold of the mantle forms a deep recess, the mantle cavity, posterior to the head and dorsal to the anterior visceral mass. In life the mantle cavity opens to the exterior via a large aperture and seawater circulates freely through it. This, the only opening to the mantle cavity, lies above the head and is bordered by the mantle skirt (Fig 3) (= mantle flap or mantle collar) which is the anterior edge of the fold of mantle that forms the cavity.   Before extraction, the skirt lined the lip of the aperture.  Gently slip a blunt probe into the aperture to demonstrate the depth of the mantle cavity.

            Notice that the left anterior margin of the mantle skirt is extended to form a gutter-like siphon (Fig 2, 12-14A,B).   In life, the siphon forms a tube which is extended along the siphonal canal of the shell and out the end of it.   It is used as an inhalant canal to bring fresh seawater into the mantle cavity for sensory evaluation by the osphradium, gas exchange by the gill, and evacuation of wastes from the anus and kidney.   The highly mobile siphon moves continuously to sample the water ahead as the snail moves.

Mantle Cavity

            Most of the organs in the mantle cavity are visible through its roof or through the anterior opening.   Looking through the roof of the mantle cavity one can easily see the slender, dark, elliptical, reddish osphradium (Fig 3, 4) on the far left and the much larger, paler, elliptical, brown gill also on the left but nearer the midline.  

            A large, but inconspicuous, wide, brownish, diffuse hypobranchial gland is located to the right of the gill (Fig 4).   It is actually larger than the gill but cannot be seen to advantage from your present viewpoint.   It is a mucus-producing gland.  

            The rectum lies to the right of the hypobranchial gland (Fig 4).   The rectum and hypobranchial gland may be difficult to see at this time.   (In Buccinum a bit of it shows along the right lateral edge of the hypobranchial gland as a dark brown stripe).

            Lift the anterior dorsal margin of the mantle and look through the opening at the mantle cavity roof and relocate the organs you just found.   On the far left is the narrow, bipectinate and gill-like osphradium situated at the base of the siphon (Fig 3).   The osphradium is a sense organ that monitors the quality of the water entering the mantle cavity from the siphon.   It is chemosensory and is also sensitive to silt.  

            Medial to the osphradium is the much larger, similarly shaped, monopectinate gill. The gill and osphradium are oriented with their long axes parallel to that of the animal but are both displaced to the left of the midline.

            The hypobranchial gland is also large but is paler than the gill.   It is oriented with its long axis canted slightly across the midline to the right side of the roof of the mantle cavity (Fig 3).  

            On the right border of the hypobranchial gland you will see the conspicuous anal papilla, at the tip of which is the anus (Fig 4, 12-45B).   Insert a teasing needle into the anus to demonstrate its presence.   The small diameter anal papilla is the terminus of the much wider rectum that courses obliquely across the posterior roof of the mantle cavity but remains near the midline.

"     Open the mantle cavity with a median, longitudinal incision through its roof (Fig 4).   Use scissors to cut posteriorly from the anterior margin of the roof between the gill and the hypobranchial gland.   Extend this cut posteriorly until you reach the kidney.   Do not cut into the kidney, or into any of the organs of the roof of the mantle.   Deflect the right and left sides of the roof and examine their inner surfaces.

            Relocate and reexamine (for the third time) the osphradium, gill, hypobranchial gland, rectum, anal papilla, and anus.   Note the large diameter of the rectum as compared with the anal papilla.   The mantle cavity may contain an abundance of mucus from the hypobranchial gland.   Notice the large size of the gland and see if you can trace the mucus, if there is any, to it.   Flush the mucus and debris from the mantle cavity with jets of water from a pipet.   Note the lamellae that enhance the surface area of the hypobranchial gland.  

            Note the construction of the gill.   It is monopectinate with one row of fine gill filaments (Fig 4).   The filaments are attached along the long left margin of the gill.   This is the axis of the gill.  

            Blood in the gill is drained away by the efferent branchial artery (Fig 4) that runs along the axis.   The more primitive bipectinate gills of patellogastropods and vetigastropods (e.g.Pectura or Diodora) have two rows of filaments along a central axis.   Look at the surface of the gill with a hand lens or dissecting microscope and note how the gill increases the surface area available for gas exchange.  

            Look inside the mantle cavity on the surface of the anterior part of the kidney for the large slit-shaped nephridiopore (Fig 4).   It is at the far posterior end of the mantle cavity.   Note that it, like the anus, is downstream from the gill.   Review the flow of water through the mantle cavity and list, in order, the structures passed by the water after it enters the inhalant siphon.  

Internal Anatomy

Reproductive System

            Busycon and Buccinum, like most prosobranchs, are gonochoric. The single gonad is located at the apex of the visceral mass (Fig 3, 4, 12-56).   The gonad lies in a coelomic space, the gonocoel, and connects with the exterior via a long gonoduct running along the right side of the body to open into the right side of the mantle cavity.  

            Fertilization is internal, with copulation, and the gonoduct is complicated.   It is composed of three sections derived from, in order from proximal to distal: the old coelomoduct of the gonocoel, part of the right nephridium and its duct, and modified areas of the mantle epithelium.   The gonoduct occupies a superficial position on the right side of the body and no dissection is needed to expose it.  


            The testis in the upper visceral mass opens into a highly convoluted vas deferens on the right side of the visceral mass (Fig 4, 12-56B).   The proximal, and most convoluted, region is sometimes called the seminal vesicle.   It becomes less convoluted and runs into the enormousprostate gland on the right side.   The gonoduct exits the prostate and continues anteriorly across the floor of the mantle cavity into the shaft of the penis (Fig 4).   It ends at the male gonopore at the tip of the penis.


            The ovary in the visceral mass opens into a slender, relatively straight oviduct that runs along the right side of the upper visceral mass (Fig 12-56A).   (The ovary of Buccinum is reddish brown).   The oviduct may be difficult to see unless it has eggs in it.   When it reaches the anterior half of the visceral mass ventral to the mantle cavity it expands into the albumen gland (creamy white in Buccinum).   A channel runs anteriorly from the albumen gland along the floor of the adjacent egg capsule gland.   This gland can be enormous.   A small seminal receptacle (or sperm ingesting gland) opens into the channel between the albumen gland and the egg capsule gland.   Anterior to the egg capsule gland a short, thick duct runs to the female gonopore on the floor of the right side of the mantle cavity.   The expanded portion of the gonoduct between the egg capsule gland and the gonopore is the copulatory bursa (or vestibule, Fig 12-56A).  

            On the sole of the foot you will find a short, but conspicuous, transverse slit located on the midline just anterior to the center of the foot.   (It is farther anterior in Buccinum).   This is the opening of a pocket, the pedal gland, which is also part of the female reproductive system .

            Eggs are produced by the ovary and move through the posterior oviduct to the albumen gland where they receive a coating of albumen.   They pass through the egg capsule gland where clusters of several eggs are together invested with a soft, malleable, protein coating that will harden to become the egg capsule.   This clutch of eggs, with its protein sheath, moves through the distal oviduct to the female gonopore and then into the pedal gland where the still soft protein is molded into a species-specific shape and attached to an appropriate substratum before it hardens. The eggs develop in the egg capsule and then escape as veliger larvae or juvenile snails.

            Busycon females secrete a very large (up to 100 cm in length), distinctive egg case (Fig 12-57A). It is a chain of about 100 proteinaceous egg capsules, each with an average of 40 eggs.   Each capsule is a flat, hollow disc about 2.5 cm in diameter and 4-8 mm thick.   The capsules are held together in a helical column by a longitudinal protein cord (Fig 12-57A). One end of the egg case is composed of sterile capsules and is buried in the sand to serve as an anchor.   The free end of the cord, with fertile capsules, lies on the surface of the sand. Development is direct and occurs in the egg capsule. Tiny, shelled, crawling juveniles about four millimeters in length exit a pore in the side of their disc and adopt an independent life. There is no veliger larva.       

Hemal System

            Relocate the translucent, membranous pericardium surrounding the pericardial cavity on the surface of the visceral mass immediately posterior to the gill (Fig 4, 12-45A,B).   Open the pericardium and find the heart inside it.   The heart consists of a ventricle and a single atrium, which is the left atrium.  The atrium is anterior to the larger ventricle.   (Buccinum:   The ventricle is a conspicuous, opaque, spherical, creamy-white structure filling most of the pericardial cavity.   The atrium, which cannot be seen until the pericardium is removed, is a thin-walled, transparent sac on the anterior wall of the ventricle.)   The efferent branchial vessel running along the left margin (axis) of the gill drains directly into the atrium and is the only source of blood for the heart.

"     With fine scissors open the atrium to find the opening of the efferent branchial vessel on its anterior wall.   The atrioventricular aperture leading from the atrium to the ventricle is on the posterior wall of the atrium.

            Look into the pericardial cavity at the ventral, medial corner of the ventricle.   This is the point of exit of the aorta, which is the only outflow of blood from the heart.   The aorta penetrates the pericardium and immediately divides into an anterior aorta (= cephalic aorta) to the anterior body and a posterior aorta (= visceral aorta) to the posterior body.

            Blood exits the ventricle via the aortae to the hemocoels where materials (wastes, nutriment, gasses, hormones, etc.) are exchanged with the tissues (Fig 12-54-2).   Blood in the hemocoel flows over the kidney and enters the afferent branchial vessel to the gill.   Following oxygenation in the gill the blood travels via the efferent branchial vessel to the atrium and thence to the ventricle.

Excretory System

            The excretory system consists of the single, large, brown left nephridium which you saw on the right side of the visceral mass (Fig 4).   The nephridium is divided into two parts.   Earlier you saw its nephridiopore opening into the posterior mantle cavity (Fig 4).   A renopericardial canal connects the pericardial cavity with the interior of the nephridium. An ultrafiltrate of the blood is produced in the pericardial cavity from which it flows through the renopericardial canal to the nephridium for modification (Fig 12-52).   The final urine is released from the nephridiopore into the posterior mantle cavity.

Digestive System

            If you have not already done so, reach into the proboscis pore with a forceps, grasp the proboscis and pull it out as far as it will come in response to gentle pressure.   Find the mouth at the distal end of the proboscis (Fig 2, 12-45B).  

"     Carefully open the proboscis with a shallow, middorsal, longitudinal incision made with fine scissors.   Begin at the mouth and cut posteriorly on the dorsal midline with the scissors but cut through the dorsal wall of the proboscis only.   Do not open the lumen of the gut tube in the interior of the proboscis.   The tubular gut lies immediately beneath the dorsal surface and adheres tightly to it.   It should not be cut yet.  

            Extend the incision posteriorly, through the head, to the proximal end of the proboscis.   This will be at the level of the posterior edge of the head and to reach it you will have to bisect the head.  

            Tease away the connective tissue as necessary and deflect the cut edges of the proboscis wall to study the structures inside.   Here you will see a complicated association of organs and structures, including the anterior gut, radula, odontophore, and a complex of specialized muscles that operate the radula and odontophore.   The odontophore and radula muscles are red in living animals due to the presence of myoglobin.   Be careful that you do not destroy the muscles.   Notice the large longitudinal proboscis retractor muscles originating at the base of the proboscis.

"     Open the anterior gut with a middorsal incision made with fine scissors inserted into the mouth.   The mouth opens into the buccal cavity in the anterior proboscis. The muscular posterior region of the buccal cavity is sometimes referred to as the pharynx.  

            The radular sac is a deep pouch on the posterior wall of the buccal cavity.   The anterior tip of the radula protrudes out of the sac into the buccal cavity.   The two edges of the radula are rolled dorsally and are separated by a mid-dorsal, longitudinal groove.   Push the edges apart and look at the radula with a hand lens or dissecting microscope.   Note its teeth.   During feeding the radula is extended from the mouth.   The radula is supported by the odontophore and when in operation the curled sides of the radula are flattened over the odontophore.

            The long, flat, white, narrow esophagus extends posteriorly from the buccal cavity. It is a very long tube passing through most of the length of the proboscis, under the floor of the mantle cavity, and deep into the visceral mass where it joins the stomach (Fig 12-45B).   In the anterior proboscis, ventral to the anterior end of the esophagus, is the conspicuous, red, muscularradular mass, which contains the radula, the odontophore, and a complex of myoglobin-rich muscles.   The odontophore is composed of a material, chondroid, that resembles vertebrate cartilage histologically but differs from it chemically.  

            The odontophore is composed of two parts, called bolsters, which are fused anteriorly but are widely divergent posteriorly.   The odontophore is shaped like a long narrow wishbone (furcula) from a chicken or turkey.   The two bolsters are located ventrally within the radular mass and the divergent posterior ends are easily seen.   The stiff chondroid bolsters can be felt with a forceps by squeezing the ventral edges of the muscle mass.

            Numerous extrinsic and intrinsic muscles, including radular protractors and retractors and odontophore protractors and retractors, make up the red muscle mass.   Try to determine the functions of some of the muscles.   Look for muscles you think may be protractors and retractors of the radula and odontophore.   Look for proboscis retractors.

            Look for the posterior end of the radula between the two divergent horns of the bolsters at the posterior end of the mass.   It is enclosed in the posterior end of the membranousradular sac.   The radula and sac form a pale, median cylinder lying dorsally between the two sides of the muscle mass.   Anteriorly it is covered by a thin sheet of muscle and is not visible without cutting the muscle.  

      >1a. While watching the anterior tip of the radula under magnification, pull gently back and forth on the posterior end of the radular sac.   Watch the radular teeth turn out into their feeding position and then roll back in. <

            Look again at the esophagus, which should be now exposed for the entire length of the proboscis.  

"     Extend the existing mid-dorsal incision posteriorly (shallowly) along the floor of the mantle cavity to the posterior end of the cavity beside the posterior tip of the gill.  

            Follow the esophagus posteriorly into the floor of the mantle cavity by cutting through the muscles (white, not red) and connective tissue in this area.   Just posterior to head and the base of the proboscis, the esophagus turns sharply ventrally into the spacious hemocoel (Fig 12-45B, 12-54A).  

            Cut the strands of white muscle on both sides of the esophagus and hemocoel to improve your access to the viscera in the hemocoel.   On its floor are located a large white ribbon, which is the anterior aorta, and a long, thin, brownish organ called Leiblein's gland, which produces hydrolytic enzymes.  

            Continue tracing the esophagus as it extends ventrally along the anterior wall of the hemocoel to the ventral floor of the hemocoel.   It is oriented vertically in this region.  

            Laterally, on the anterior wall of the hemocoel, is a pair of large salivary glands.   They are pale yellow or creamy white and they connect, via long ducts, to the esophagus in the vicinity of the nerve ring (Fig 12-54A).   (In Buccinum these ducts run the entire length of the esophagus to empty into the buccal cavity.   They lie on either side of the esophagus and are convoluted.)  

            There is a salivary gland on either side of the vertical portion of the esophagus.   The right salivary gland is closer to the esophagus than is the left.   At this point the esophagus is encircled by the circumesophageal nerve ring, or brain.   The nerve ring is purplish red due to the neuroglobin contained in the nerve tissue (yellow or orange in Buccinum).   The nerve ring is hidden by the salivary glands.   Be careful that you do not damage the ring or the numerous brownish nerves associated with it.   You will return to study the nerve ring later.

            The esophagus passes through the nerve ring and immediately undergoes its second change in direction to end its downward journey and turn posteriorly again (Fig 12-45B).   It now passes horizontally over the floor of the hemocoel.   It also swings over to the left side and no longer lies on the midline.  

            The anterior aorta also lies in this region and may be confused with the esophagus.   The aorta more or less parallels the esophagus but crosses dorsally over the esophagus just posterior to the nerve ring.   It branches posterior to the nerve ring, something the esophagus does not do, of course.   (In Buccinum the aorta is smaller than the esophagus).   The only way to be sure which is which is to trace them to their origins or find the branching point of the aorta.  

            Just posterior to the nerve ring, the esophagus receives a duct from the long, thin Leiblein's gland.   This gland resembles the esophagus and aorta, to further complicate matters.   The gland is attached to the esophagus immediately posterior to the nerve ring and is a long, narrow tube, slightly darker than the aorta or the esophagus.   Leiblein's gland extends to the posterior end of the hemocoel below the mantle cavity.

            Trace the esophagus posteriorly along the floor of the hemocoel being very careful of the aorta which covers it.   The floor of the mantle cavity narrows to a point posteriorly and the esophagus, aorta, and Leiblein's gland converge on this point.   Look a little to the right of this point, on the floor of the mantle cavity, for the two pink visceral ganglia lying beside each other (yellowish in Buccinum).

"     Cut through the necessary tissue to trace the esophagus out of the hemocoel and into the visceral mass posteroventral to the pericardial cavity. The esophagus is easiest to trace by opening it and following its lumen. (Buccinum:  Where the esophagus leaves the hemocoel it changes from white to pink, increases in diameter, becomes thick-walled and muscular, and bears a small diverticulum.)

            The esophagus runs ventral to the heart along the left side of the digestive cecum to join the posterior end of the stomach.   This terminal portion of the esophagus is pink and lies partly exposed on the surface of the visceral mass. A branch of the posterior aorta may be seen on its surface.  

            The stomach is embedded in the left side of the digestive cecum a short distance posterior to the heart (Fig 12-45B).   A conspicuous branch of the posterior aorta courses over its surface.   The stomach is transparent and darker brown than the greenish digestive cecum which surrounds it.   (Buccinum: the stomach is pale whitish and the digestive cecum is brown).   The stomach is elongate.   Near its posterior ventral extremity it receives the pink esophagus that runs posteriorly from the region of the heart.

            Follow the stomach anteriorly, back towards the heart, from the point of entrance of the esophagus near its posterior end.   The stomach narrows as it approaches the anterior end of the visceral mass and there becomes the intestine.   The walls of the stomach receive the ducts from the digestive cecum.

            The short intestine curves across the rounded, anterior end of the digestive cecum, along the border of the kidney, to enter the roof of the mantle cavity (Fig 12-45B).   Here the gut, now the rectum, passes lateral to the hypobranchial gland and is covered (when viewed from the outside) by the egg capsule gland of the female (Fig 4, 12-45B).   The rectum terminates at theanus atop the anal papilla (Fig 4).

Nervous System

            Busycon has a highly cephalized nervous system with all the typical molluscan ganglia, except the visceral, participating in the circumesophageal nerve ring around the midregion of the esophagus (Fig   12-54A, 12-53, 12-45B, 12-17B).   The visceral ganglia, which are more posterior, are not associated with the ring.

            " Remove the salivary glands, clear the white muscle and connective tissue away from the pink or yellow (in life) nervous system, and look at the nerve ring under magnification.  The color of the ganglia is due to the presence of neuroglobin in the tissue.

            Lying dorsolaterally on the top and sides of the esophagus are the two large cerebral ganglia (Fig 5, 12-54A).   The two cerebral ganglia are connected by a short broad cerebral commissure across the midline.   The cerebral ganglia and cerebral commissure form the top of the nerve ring.    

"   Cut the commissure and deflect it and the two cerebral ganglia.   Cut the esophagus anterior to the ring and deflect it posteriorly.   Remove the connective tissue investing the ganglia of the nerve ring so you can see the ring and its ganglia clearly.

            The two fused pedal ganglia are ventral to the esophagus and form the ventral portion of the ring (Fig 5, 12-54A, 12-53).   They are connected to each other across the midline by thepedal commissure and to the cerebral ganglia by cerebro-pedal connectives around the sides of the esophagus.   These ganglia and their connectives and commissures form thecircumesophageal nerve ring.  

            List in order, beginning with the right cerebral ganglion and proceeding clockwise, the components of the nerve ring. There is a second nerve ring posterior to the first.   It also involves the cerebral ganglia dorsally but ventrally includes the two pleural ganglia (Fig 5, 12-53).

            The two visceral ganglia, which you found earlier, lie close together in the thin tissue connecting the posterior wall of the hemocoel with the visceral mass (12-53).   They are adjacent to and to the right of the esophagus in this region.   The visceral ganglia are joined to the nerve ring by the longitudinal visceral nerves from the pleural ganglia.   The esophageal ganglia are located on the visceral nerves.

            The two esophageal ganglia (= parietal ganglia or intestinal ganglia) remain associated with the visceral nerves as they are in the ancestral gastropods (Fig 12-17B) but have moved much closer to the nerve ring in neogastropods (Fig 5). The left esophageal ganglion (= subesophageal ganglion) is embedded in the ring (Fig 5).   The right esophageal ganglion (= supraesophageal ganglion) is attached to the right pleural ganglion a little outside the ring (Fig 5).   The right and left visceral nerves extend from the esophageal ganglia to the visceral ganglion.

            The visceral nerves extend posteriorly from the right and left esophageal ganglia posteriorly to the visceral ganglia to form the asymmetrical visceral loop.   The asymmetry of this loop is due to torsion.   The right and left esophageal ganglia of the untorted and symmetrical ancestral mollusc end up on sides opposite their original positions.

Figure 5.   Dorsal view of the nerve ring of Buccinum undatum.   The cerebral commissure has been cut and its ends deflected to opposite sides of the drawing. Gastrop162L.gif

Figure 5

               Nerves from these many ganglia innervate the body.   In general, the nerves of the cerebral ganglia are sensory from the sense organs of the head.   The pedal ganglia send motor nerves to the foot musculature and the pleural ganglia serve the siphon and other parts of the mantle.   The esophageal ganglia serve the mantle skirt, gill and osphradium. The buccal ganglia send motor nerves to the muscles of the buccal mass. The visceral ganglia have visceral sensory and motor input and output vis a vis the viscera.


            Abbott DP .   1987.   Observing Marine Invertebrates.   Stanford University Press, Palo Alto.   380 p.   (Nucella emarginata, Nassarius, and Acanthina spirata)

            Bullough WS.   1958.   Practical Invertebrate Anatomy.   MacMillan, London.   483 p.   (Buccinum)

            Cox LR.   1960.   Gastropoda, in RC Moore (ed).   Treatise on invertebrate paleontology, I (1): I 84- I 169.   Geological Society of America

            Dakin WJ.   1912.   Buccinum.   Mem. Liverpool Mar. Biol. Com. 20:1-123, 8 pls.

            Fretter V, Graham A.   1994.   British Prosobranch Molluscs, 2 nd ed.   Ray Society, London.   820 pp.

            Purchon RD.   1977.   The Biology of the Mollusca.   Pergamon, Oxford.   560p.

            Pierce ME.   1950.   Busycon canaliculatum.   in F. A. Brown (ed) Selected Invertebrate Types.   Wiley, New York.   pp 336-344.

Ruppert EE, Fox RS, Barnes RB.   2004. Invertebrate Zoology, A functional evolutionary approach, 7 th ed. Brooks Cole Thomson, Belmont CA. 963 pp.


Compound microscope (optional)

Living or preserved snail

Concentrated magnesium chloride

Vise  or C-clamp (for Buccinum)

Hammer and cold chisel (for Busycon)

Large dissecting pan

Safety glasses


Slides, coverslips

Living Busycon is sold by Woods Hole Marine Biological Lab asBusycotypus.