Invertebrate Anatomy OnLine
Diodora cayenensis ©
Copyright 2003 by
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 to 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.
Eumollusca, Conchifera, Ganglionura, Rhacopoda, Gastropoda C,
Prosobranchia sC, Vetigastropoda O,
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
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
coelom is reduced to small spaces including the pericardial cavity containing
the heart and the gonocoel containing the gonad.
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.
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.
is the sister taxon of Aplacophora and includes all molluscs other than
eumolluscan gut has digestive ceca which are lacking in aplacophorans, the gut
is coiled, and a complex radular musculature is present.
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.
Recent molluscs are ganglioneurans, only the small taxa Aplacophora,
Polyplacophora, and Monoplacophora are excluded. Neuron cell bodies are
localized in ganglia.
mantle cavity is posterior in the ancestor although it may be secondarily moved
anterior by torsion. This taxon includes gastropods and cephalopods.
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 most 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
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).
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
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
often known as archaeogastropods, have characteristics that in traditional
phylogenies place them close to the ancestry of gastropods. The
taxon includes keyhole limpets, slit snails, abalones, top and turban snails.
have traditionally been considered to be the most primitive living gastropods
(although there is some evidence that honor may belong to patellogastropods). In
zeugobranchs we see many features expected of the ancestral gastropod. The
mantle cavity is anterior as a consequence of torsion. Two
gills are present and are bipectinate. Zeugobranchs
are diotocardian, with two atria, and blood from each gill drains into its own
atrium, right or left. The
atria drain into a single median ventricle. The
nephridia are paired (but the left is much smaller than the right and apparently
has little or no function). A
single large gonad releases its products through the duct of the right
gonad is separated from the pericardial cavity.
shell has a unique second aperture by which waste products are vented,
presumably to avoid fouling the two gills. Surviving
Zeugobranchia are the slit snails, abalones, and keyhole limpets. All
are torted but may or may not be coiled as adults.
limpets are symmetrical and uncoiled, although this condition is secondary, not
shell is equipped with an anal pore or anal slit.
species of Fissurellidae can be used with this account of the anatomy of Diodora
cayenensis but it will apply
best to species of Diodora. Diodora
cayenensis is a common species
occurring from Maryland to Brazil on the American Atlantic coast. Diodora
aspera occurs in shallow water
from Alaska to Baja California on the Pacific Coast. Megathura
crenulata is a large keyhole
limpet found in southern and Baja California. Diodora
apertura occurs on the west
coast of Britain. Diodora
dysoni occurs in south Florida
and the Caribbean south to Brazil.
zeugobranchs, keyhole limpets are good examples of the predicted ancestral
gastropod condition with respect to the atria, nephridia, gills, and the pattern
of water circulation through the mantle cavity. Furthermore,
keyhole limpets are symmetrical and uncoiled. Most of the important features
illustrating the zeugobranch condition can be studied without opening the body
of the animal. It
is necessary to remove the shell and open the mantle cavity but further
dissection is not required. Interested
students are encouraged, as always, to proceed beyond the written instructions
and may investigate the internal anatomy if they wish and time permits.
specimens should be relaxed and dissected in isotonic magnesium chloride. Preserved
material should be dissected submersed in tapwater. The
dissection should be conducted in a small dissecting pan on the stage of a
the animal from its shell using a scalpel to scrape (not cut) the soft tissue
away from its attachment to the shell. Insert
the blade of the scalpel between the body and the shell and work it completely
around the circumference of the shell. Keep
the blade in contact with the shell at all times and do not cut any tissues. The
horseshoe-shaped attachment (insertion) of the pedal retractor muscle adheres
tightly to the shell (in living specimens) and is hardest part to free.
shell may be studied attached to the animal or separately. The shell of
keyhole limpets is a single piece shaped like a broad oval cone, resembling a
volcano, complete with a crater at the summit (Fig 1). The
shell is not coiled and is bilaterally symmetrical (Fig 12-22A). While
this symmetrical condition resembles the hypothesized condition of the shell of
the ancient prosobranch ancestor, in fissurellids it is not primitive. Keyhole
limpets arise from ancestors with coiled shells and, indeed, each individual
begins life with an asymmetrical coiled shell but loses all but the large body
whorl during development.
Figure 1. Dorsal
and side views of the shell of a keyhole limpet, Diodora. Gastrop150La.gif
the interior of the shell. Note
the lustrous, smooth, nacreous innermost layer. It
is secreted by the entire dorsal surface of the mantle. Look
for the horseshoe-shaped pedal
retractor muscle scar. It
is the insertion site of the pedal retractor muscle but is indistinct and you
may not find it.
shell forms a shield over the dorsal surface of the animal but does not provide
a commodious retreat as do the shells of higher gastropods. Unlike
the shells of all other gastropods, those of keyhole limpets have two openings. The
broad open base of the cone is the large aperture from
which the foot and head protrude. It
is homologous to the aperture of other gastropod shells.
second opening is the much smaller anal
pore situated at the apex,
or summit, of the cone (Fig 1). It
is the "crater" of the “volcano” mentioned above. In Diodora the
anal pore is displaced toward the anterior end and is not in the center of the
presence of the anal pore distinguishes the keyhole limpets from the several
other (unrelated) kinds of limpets and is responsible for the common name
anal pore is the adult remnant of a large marginal anal slit in the shell of the
developing juvenile (Fig 12-26).
outside of the shell is variously ornamented with radial and concentric ridges,
scales, beads, or spines depending on species (Fig 1). The
interior is smooth and glossy.
bilaterally symmetrical and the adult shows no signs of coiling, although it is
torted. The visceral mass and mantle cavity are rotated 180 ° counterclockwise
with respect to the foot, thus placing the mantle cavity and anus at the
anterior end and identifying the limpet as a gastropod.
the body of the animal. The
dorsal body wall (mantle) is very thin and transparent so that most of the
organs in the visceral mass can be seen without further dissection or, at the
most, by opening the mantle cavity.
body consists of the foot, visceral mass, and head. The
large, muscular, oval foot occupies
the entire ventral surface (Fig 2). It
is broad and flat and is used for adhering to and creeping over hard substrata.
foot normally extends below and outside the margins of the shell but when
threatened the shell can be pulled ventrally to contact the substratum and
protect the soft parts, including the foot.
foot is attached to the ventral surface of the shell by a large U-shaped (in
frontal section) pedal
retractor muscle (Fig 2)
derived from the separate right and left pedal retractor muscles of ancestral
gastropods (Fig 12-26). The
open end of the "U" faces anteriorly. When
this muscle contracts, it pulls the shell toward the foot, which is normally
attached to the substratum, so the shell is thus pulled against the substratum.
columellar muscle of coiled gastropods is derived from the pedal retractors. In
coiled gastropods only the right pedal retractor muscle is present, as the
columellar muscles, and it is responsible for withdrawing the foot into the
aperture of the shell. It
extends from the central axis of the coiled shell (the columella) to the foot. This
is essentially the same action, origin, and insertion as the pedal retractor
muscle of keyhole limpets.
longitudinal row of small papillae, the epipodial
tentacles. Extends along the
dorsal edge of the foot on each side of the body. It
has been claimed, but not substantiated, that these are repugnatorial but their
innervation suggests a sensory function.
the head and posterior end of the foot to the wax of the dissecting pan using a
#l insect pin at each end.
The head is
located dorsal to the foot at the anterior end of the visceral mass (Fig 2,
12-22B). The visceral mass contains
most of the visceral organs and occupies most of the interior of the shell. It
is situated above the foot and is always covered by the shell. It
will be studied in more detail later.
cylindrical, tubular snout is
directed ventrally and slightly anteriorly from the head. The mouth is
located at the center of the distal end of the snout.
pair of cephalic tentacles extends
from the dorsolateral corners of the head (Fig 2). Each
bears a lateral eye at
anterior-most right epipodial tentacle is immediately posterior to the right
cephalic tentacle. It
closely resembles, in shape and position, the penis of higher prosobranch
gastropods and has been mistaken for than organ. It
is present in both sexes, however, and appears to have a sensory, rather than a
Mantle and Mantle Cavity
The mantle is
the dorsal body wall of the visceral mass. It
is attached to the inside of the shell above the visceral mass. Peripherally
the mantle protrudes from beneath the shell as a prominent fold of the body
wall, called the mantle skirt. The
skirt forms a collar around the aperture. It
is formed into three folds and is homologous to the enormous mantle skirt of
bivalves, which also bears three folds (usually).
outer fold is the smallest. It
lies against the edge of the shell and its lateral, or outer, surface secretes
the middle, prismatic, layer of the shell. The
medial surface of the outer fold is thought to secrete the outer shell layer, or
innermost, lamellar, nacreous shell layer is secreted by the entire outer
surface of the mantle and not by a fold. Shell
secretion in gastropods has not been carefully studied and the much of our
knowledge of the subject is based on extrapolations what is known of bivalves.
middle mantle fold is sensory and bears numerous mantle
tentacles (Fig 2). The
medial, or inner, fold of the mantle margin is the largest and is muscular. Muscles
arising in this fold insert on the inner surface of the shell near the margin of
the aperture. These
muscles attach the mantle to the shell.
the mantle overhangs a deep, median recess, the mantle
cavity proper. This
cavity is open to the sea via a large anterior opening above the head. The
cavity itself lies above the anterior visceral mass and under the anterior
a probe or needle to lift the mantle skirt and demonstrate the presence of the
the mantle skirt overhangs a longitudinal channel called the pallial
groove (pallial = mantle) on
the side of the animal between the foot and the visceral mass. It
is a lateral extension of the anterior mantle cavity but by no means as deep.
The epipodial tentacles, arrayed in a longitudinal row, protrude into the
pallial groove. They
arise from the lateral body wall immediately dorsal to the foot. Do
not confuse the epipodial tentacles with the mantle tentacles of the middle
the head ventrally and look into the anterior mantle cavity again. The
most conspicuous structures in it are the two bipectinate gills (Fig
2, 12-22B). The
presence of two gills is one of the reasons for studying this animal. Among
all prosobranch gastropods it is only zeugobranch vetigastropods that have two
gills, the presumed ancestral condition. In
all others the right gill is lost.
anterior ends of the horseshoe-shaped pedal
retractor muscle form the
lateral walls of the mantle cavity (Fig 2).
the dorsal opening in the posterior roof of the mantle cavity and note the short
sensory tentacles around it. This
is the exhalant aperture from
the mantle cavity (Fig 2). Its
position coincides with that of the anal pore at the summit of the shell.
the mantle cavity with a median, dorsal, longitudinal incision through its roof. Use
fine scissors and begin the incision at the anterior edge of the mantle, above
the head, and cut posteriorly to the exhalant aperture. Deflect
and pin the roof of the mantle cavity and examine its interior.
Figure 2. Dorsal
view of Diodora dysoni from
Big Pine Key, Florida. The
shell has been removed and mantle cavity has been opened with a median incision
and its two sides deflected. Gastrop151La.gif
two large, triangular, bipectinate gills fill
most of the mantle cavity (Fig. 2, 12-22B). The efferent
membrane attaches them by
their narrow bases and part of their lateral (efferent) borders to the floor of
the mantle cavity. Their
tapered apices protrude anteriorly out of the mantle cavity.
gill has a central axis from
which arise two rows of sheetlike filaments,
one on each side of the axis. It
is the presence of two rows
of filaments on each gill that makes these gillsbipectinate. Bipectinate
gills are predicted for the ancestral gastropod. The
gills of higher prosobranchs (mesogastropods and neogastropods) are
monopectinate with only one row of filaments. An
inconspicuous osphradium is located along the medial side of the base of the
efferent membrane, parallel to and beside the gill axis.
is a pair of hypobranchial
glands in the posterior roof
of the mantle cavity, above the bases of the gills.
The anus opens
into the posterior end of the mantle cavity on top of a short anal
papilla between the bases of
the gills (Fig 2, 12-22B). The
similar urogenital papilla is
located to the right and slightly ventral to the anal papilla (Fig 2, 12-22B). The
gonad and right kidney open via the urogenital
pore at the end of this
vestigial left kidney opens via a tiny inconspicuous pore located to the left of
the anal papilla (Fig 12-22B). It
is difficult to find. The
anus and urogenital papillae are is immediately ventral to the exhalant aperture
and anal pore.
looking into the open mantle cavity, mentally trace the flow of water through it
(Fig 12-22B). Water
enters anterolaterally, on both sides
of the head, flows posteriorly and medially over the osphradia and gill
filaments, over the nephridiopore, and over the anus. It
then turns dorsally to exit via the exhalant aperture and anal pore. This
arrangement allows water to enter on both sides of the head and flow over both
gills and the anus without running the risk of fouling the gills or the mouth
with feces, urine, or gametes. It
requires, of course, the presence of an anal pore for the exhalant current.
higher vetigastropods, mesogastropods, and neogastropods there is no anal pore
or its equivalent and the respiratory water current must enter and leave
the left gill is present in the higher snails and water enters the left anterior
side of the mantle cavity, flows over this gill, then over the anus on the right
side of the mantle cavity and then out the right anterior side of the cavity.
at the roof of the visceral mass posterior to the mantle cavity. The
transparent, colorless pericardial
cavity is located
immediately posterior to the junction of the bases of the two gills (Fig 2). In
it is located the diotocardian heart. This
organ consists of a single central ventricle and
two lateral atria.
swollen, transparent atrium is located on the postero-lateral corner of each gill,
beside the median ventricle. A
narrow efferent branchial
vessel lies along the
lateral border of each gill (Fig 2). Oxygenated
blood drains from the lateral edge of the gill into this vessel. The
vessel in turn empties into its atrium which opens to the ventricle. Contractions
of the ventricle force oxygenated blood into the aorta to the body.
right and left metanephridia,
or kidneys, are present, the right is much larger than the left (Fig 2). The
right nephridium is a pale yellow (in life), folded, saccate organ lying
immediately posterior to, and partly covered by, the ventricle. Its
lumen is connected to the pericardial cavity by a renopericardial canal, which
you will probably not see. The
right nephridium opens to the exterior by a nephridiopore on the tip of the
left nephridium is present but it is small and vestigial. It
is a simple, ciliated sac that opens into the posterior mantle cavity via a tiny
nephridiopore on the posterior wall of the mantle cavity to the left of the
has no connection with the pericardial cavity and its function is not known.
right nephridium is lost in higher prosobranchs and in them the left nephridium
persists and is important as the only complete functional nephridium. All
that remains of the right nephridium of higher gastropods is a small region that
contributes to the genital duct.
of the digestive system is hidden from view by other organs lying over it and
cannot be seen without opening the body. There
follows a brief account of the anatomy of the gut but it is not intended as
dissection instructions and you should not attempt to open the gut or visceral
mass at this time. After
you have completed the study of externally visible anatomy you may return to
this section as use it as a guide to help you find the most conspicuous internal
features if you wish. At
present find only the structures in bold type. They
are visible from the exterior without further dissection.
ventral mouth opens
into a small buccal cavity. The
radula lies in a pouch, the radular sac, off the floor of the buccal cavity. The
esophagus extends posteriorly to the stomach on the left side of the visceral
walls of the esophagus are expanded to form a large glandular region. The
stomach is pyriform with its swollen end posterior.
style sac is the narrow anterior end of the stomach and may be visible at the
surface of the visceral mass to the left of the nephridium and ventricle. The
style sac contains a rotating mass of feces and mucus (the protostyle) but no
crystalline style. The
stomach conforms with the prediction for the ancestral mollusc except for the
effects of torsion. Because
of torsion, the esophagus enters the bulbous posterior end
of the stomach and the intestine exits the narrow anterior end. Torsion
bends the gut into a "U" at the level of the stomach and reverses the customary
relative positions of the esophagus and intestine.
gastric cecum is associated with the stomach. There
is a chitinous gastric shield in the posterior stomach and two ducts from the
digestive ceca open here. The
stomach walls have a sorting field of ciliated ridges and grooves. Two
typhlosoles border a ciliated intestinal groove that extends along the style sac
into the intestine.
intestine exits the style sac at the narrow anterior end of the stomach and
makes a single loop to end up on the midline as the rectum (Fig
terminal region of the intestine is visible on the dorsal midline where it
passes through the pericardial cavity and ventricle to end at the anal papilla
mollusc intestine is minimally involved in digestion and absorption and its
major role is compaction of the feces into pellets. A
long intestine is usually associated with the need to package the feces into
pellets that will not disintegrate in the mantle cavity and foul the gills or
intestine of Diodora is
short and does not make fecal pellets. The
presence of the anal pore in the fissurellids minimizes the danger of fouling
the gills so feces do not need to be tightly packaged. The
intestine of true limpets (e.g. Pectura),
which lack the apical aperture, is much longer and manufactures fecal pellets.
"siphon" similar to that of echiurans and echinoids parallels the intestine. It
is a small-diameter ciliated tube that diverges from the anterior intestine just
below the style sac and then rejoins it near the anus. It
is formed by the closing of the intestinal groove but its function is unknown. In
other invertebrates with such a structure its function is to shunt large amounts
of inadvertently ingested water past the stomach and avoid thereby dilution of
of the two large, dark digestive
ceca can be seen on the
surface of the visceral mass (Fig 2). Combined,
the ceca are the largest organ in the visceral mass and the most conspicuous
organ on the surface of the mass. Each
cecum is connected to the stomach via its own duct. The
ceca are hollow and composed of an abundance of tiny branching tubules that
eventually connect with the stomach.
digestive ceca secrete hydrolytic enzymes and release them into the stomach
where extracellular digestion begins. The
products of hydrolysis and particulates move into the digestive ceca where
extracellular digestion continues. The
products of digestion are absorbed by the epithelium of the ceca. In
zeugobranchs there is also some phagocytosis and intracellular digestion in the
digestive ceca. The
digestive ceca is surrounded by the hemocoel and immersed in blood.
are browsers on hard substrata and the British species, Diodora
apertura, feeds on sponges (Hymeniacidon, Halichondria). You
may wish to prepare a wetmount of the contents of the rectum or stomach and
examine it for sponge spicules. Poll
the class to see if anyone has found evidence of feeding on sponges. Look
for other recognizable food items in the gut contents. <
are gonochoric and a single, large gonad,
either ovary or testis occupies much of the space in the ventral visceral mass
(Fig 2). Portions
of it are visible on the dorsal surface of the mass especially during periods of
reproductive activity. This
single gonad is thought to be homologous to the right gonad of the ancestral
gonad is not intermingled with the digestive ceca. The
gonad empties to the exterior via the lumen of the right nephridium. The
duct from the gonad opens into the renopericardial canal between the pericardial
cavity and the right nephridium (Fig 12-26). Gametes
pass through the canal into the lumen of the nephridium and then exit into the
mantle cavity via the urogenital pore on the urogenital papilla.
is external and there is none of the complex elaboration of the genital duct
associated with internal fertilization seen in mesogastropods and neogastropods.
the sex of your specimen by examining the gonad. Eggs
are clearly evident and recognizable in females. Prepare a wetmount
of a small fragment of the gonad in seawater. Look
for gametes. Eggs
will be large nucleated spheres. Sperm
will be tiny and flagellated. If activated by the seawater they may be swimming. <
claim has been made, on the basis of correlations between sex and body length,
that Diodora, although
usually gonochoric, is sometimes a consecutive hermaphrodite. If
this is true, any individual you examine will be either male or female, but its
sex will change during its life. Diodora,
if it is hermaphroditc, is protandric, meaning that each individual begins life
as a male, then changes to female as it grows to its final size.
is the more common of the two forms of consecutive hermaphroditism because it
allows the animal to make sperm, which are relatively inexpensive, while it is
small and eggs, which require more resources, when it is large. The
alternative, female first then male, is protogyny and is less common.
the length of the shell of your specimen (in mm) and determine its sex if you
have not already done so. Record
these data on the chalkboard along with similar data from other students. Examine
the compiled data and see if they reveal a tendency for Diodora to
be male when small and female when large. Do
you think your species is hermaphroditic? Do
not place too much faith in conclusions based on small samples. <
is direct, there is no free-living veliger, and the young emerge from the large
yolky eggs as miniature adults.
you wish to see the digestive system in its entirety, you may dissect the
visceral mass. First
remove the very thin, transparent body wall from its dorsal surface.
this opportunity to lift gently the superficial organs so you can see those
lying deep to them. Examine
the extent of the digestive gland and the gonad and confirm the earlier
statement that they are much larger than their dorsally visible portions.
the digestive system by opening it and following its lumen through the
surrounding tissues. This
is the best way to trace the gut in almost any mollusc. Insert
one point of your finest scissors into the mouth and make a median dorsal
incision through the dorsal body wall to open the gut lumen. Follow
the gut posteriorly by opening it in this manner. Find
the regions described in the digestive system section.
least one species, Diodora
aspersa, responds in an interesting and predictable manner to predatory
asteroids (forcipitulates), or to water formerly inhabited by these sea stars. In
response to a kairomone from the star, the snail extends the mantle to cover
most of its shell. The
result is that the star’s tube feet cannot obtain the necessary grip on the
shell to pull the limpet from its rock. There
is some indication that the mantle surface may be repugnant to the star
living limpets and sea stars or other echinoderms are present in your
laboratory, make some simple tests to see if your limpet species will respond to
any of the echinoderms available. Record
the nature of the response and the combinations of limpet/echinoderm species
that elicit it. <
a living limpet crawl across a culture dish of seawater. Squirt
a little carmine/seawater in front of the snail and see if you can visualize the
respiratory current. <
a living limpet on its back in a dish of seawater and see if it can turn itself
back over. Limpets
are unusual among gastropods in their inability to right themselves. <
a living limpet with its foot down on a clean microscope slide in a dish of
animal will quickly attach to the slide, which can then be turned over and
supported above the bottom of the dish by short lengths of thick glass rod or by
other means. Examine
the foot and head of the limpet with the dissecting microscope. Find
the mouth and watch the operation of the radula as it is repeatedly protruded
and retracted (Fig 12-2). <
a small paintbrush to apply a coat of India ink to the surface of a small glass
plate or microscope slide. Let
the ink dry thoroughly. Place
the plate in a dish of seawater (but not in your aquarium) and put a limpet on
the limpet attach and crawl over the surface of the plate. With
a little luck, the limpet will scrape the surface of the slide with its radula
as it crawls across it. The
radula will remove the ink in a pattern characteristic of the species. Remove
the limpet from the glass, remove the glass from the dish, and gently rinse the
seawater from it. Let
it dry. The
plate can now be painted or sprayed with shellac or varnish and retained as a
permanent record of its species specific radular pattern. You
may want to try this with other microphagously browsing snails or chitons and
compare the patterns. <
DP. l987. Observing
Marine Invertebrates. Stanford,
Palo Alto, 380 p. (Megatebennus
bimaculatus and Fissurella
V, Graham A. l994. British
Prosobranch Molluscs, 2 nd ed. Vol
161. Ray Society, London. 820pp.
LH. 1967. The
Invertebrates, IV. Mollusca. McGraw-Hill,
New York. 792p.
Margolin AS . l964. The
mantle response of Diodora
Ruppert EE, Fox RS,
Barnes RB. 2004.
Invertebrate Zoology, A functional evolutionary approach, 7 th ed.
Brooks Cole Thomson, Belmont CA. 963 pp.
Dissecting set with microdissecting tools
other fissurellid, living or preserved
Small dissecting pan
#1 stainless steel insect pins:
Isotonic magnesium chloride for living specimens
seawater for living specimens