ADDITIONAL INFORMATION, IF ANY, CONCERNING AUTHORS, ADDRESS, TITLE, OR CITATION DATA
PLEASE TYPE ABSTRACT DOUBLE SPACED BELOW
WALKER, CATHÉRINE GENE. (Hopkins Marine Station of Stanford University,
Pacific Grove, California, USA.)
Studies on the jaw, digestive system, and Goelomic
derivatives in representatives of the genus Acmaea (Mollusca: Gastropoda: Prosobranchia)
Veliger
. -- Placement and extent of the radula sac, the
form of the jaw, the arrangement of the salivary glands, the looping of the gut,
and the interconnections of coelomic derivatives are described and illustrated for
Acmaea asmi, A. digitalis, A. limatula, A. pelta, A. scutun, A. scabra. The ratio
of radula length/shell length is nearly 2 in A. scutum and 1-1.5 in other Acmaea
species. Jaws vary in shape; the hard anterior band in A. pelta, A. insessa,
and Lottia gigantea bears an anterior median tooth. Salivary glands vary between
species in length of ducts, size and position of glands. The pattern of gut loops
hows minor but consistent differences between Acmaea species. Development of the
Fadult pattern of loops is essentially completed before animals reach a shell length of
4 mm. The gut tends to be thicker and heavier in species feeding on larger erect or
encrusting algae (A. pelta, A. limatulà, A. scutum) than in species feeding on films
of microscopic algae (47 digitalis, A. Scabra, A. asmi) Limpets from the high
intertidal zone (A. digitalisaand A. scabra) have relatively larger right and left
kidneys than do Acmaea species from lower levels.
PLEASE DO NOT TYPE BELOW THIS LINE
107
Studies on the Jaw, Digestive System,
and Coelomic Derivatives in Representatives of
the Genus Acmaea (Mollusca: Gastropoda: Prosobranchia)
By
Catherine Gene Walker
Hopkins Marine Station of Stanford University,
Pacific Grove, California
(13 Text figures; 1 Table)
Previous and contemporary workers have noted some
dietary differences between California species of Acmaea
(e.g., Test, 1945, 1946; Craig, 1966; Eaton, 1966), and
have noted some species differences in the radula and
radula strap (e.g., Test, 1945, 1946; Fritchman, 1960,
1961), which also may be related to diet. No similar
attempts have been made to compare the digestive tracts
or jaws of California limpets, though these too might
be expected to show some variation possibly related to
food habits. In the present work, the gross morphology
of the gut has been compared in the following species:
A. asmi (Middendorf, 1849); A. digitalis Eschscholtz,
1833; A. limatula Carpenter, 1864; A. pelta Eschscholtz,
1833; A. scabra (Gould, 1846); A. scutum Eschscholtz,
1833: The jaws have been studied in these six species
and also in A. insessa (Hinds, 1842), A. paradigitalis
Fritchman, 1960, and Lottia gigantea Sowerby, 1843.
(*sec tstriste )
5
106
Catherine Gene Walker
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Additional observations have been made on the development
of the digestive tract in very young Acmaea, and on the
interconnection of the coelomic cavities in the six species.
METHODS
All specimens examined were collected on Mussel
Point, near the Hopkins Marine Station, Pacific Grove,
California, and at Point Pinos and Point Joe nearby on
the Monterey Peninsula, during April and May, 1966.
Dissections were made on animals killed in 95% alcohol.
Since this type of preservation, making tissues more
pliable, introduced distortion of certain structures,
comparisons were made with fresh material also. Injection
of Ward's latex solution was used to determine placement
of gland ducts and intestinal loops. Starvation of the
animals for 3 - 5 days before injection proved helpful
in clearing the digestive tract, though injection of thee
entire tract was never successful.
GENERAL DESCRIPTION OF THE DIGESTIVE SYSTEM
The gross anatomy of the digestive tract of the
Acmaea species studied (Figures 1 and 2) is similar to
that of Acmaea virginea (Muller) as described by Fretter
and Graham (1962; pp. 149-239, 477-509), and Lottia
gigantea (see Fisher, 1904). The mouth opens ventrally
on
when the head, isinanaturelposttionor whenthelimpet
ie The lips completely encircle the elliptical
opening with a wide wrinkled border. The mouth leads
Catherine Gene Walker
-3-
into the buccal or oral cavity which contains a series
of pouches, grooves, the radula, and the naw. The radula
sac begins just behind the buccal mass and cavity.
Passing straight back over the head muscles, it enters
the anterior side of the visceral mass. It passes between
the intestinal loops and stomach, curves to the right
and forms a loop surrounded by the digestive gland, and
extends anteriorly again, rising up over the top of the
gland where often it can be seen when the shell and
dorsal body wall are removed. Reentering the head
cavity at the same point at which it left, the sac
ends in a fleshy knob or caecum which secretes the radula
(Fretter and Graham, 1962,p. 173; Runham, 1963).
The jaw, a pliable chitinous structure, is posi¬
tioned anteriodorsal to the oral cavity (Figures 2 and
6). It protects the upper lip from the scraping move¬
ment of the radula teeth, and prevents food from escaping
the buccal cavity (Fretter and Graham, 1962, p. 168).
In Acmaea and Lottia gigantea there is a single symme-
trical jaw, with four wingtlike extensions that are
opaque, white, and fairly flexible. The smaller anterior
wings overlap the posterior wings on the dorsal side.
Muscles attached to the bases of the wings run to the
body wall and buccal mass. Across the anterior mid¬
portion of the jaw runs a harder band, which becomes
reddish-brown in older animals.
110
Catherine Gene Walker
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Behind the oral cavity lie the pharynx dilation,
and the esophagus. The latter extends backward to enter
the visceral mass slightly to the left of the midline.
Curving to the right it passes upward through the
digestive gland and ends just under the dorsal surface
of the gland inna mid-dorsal position. The greater
and lesser folds of the esophagus follow the course
described by Fisher (1906, pp. 10-11) in Lottia. The
lesser fold begins in the mid-ventral region of the
pharynx, twists counter-clockwise as viewed from the
rear, and finally reaches a dorsal position just before
it ends. The greater folds, which begin dorsally, are
twwisted so they come to lie ventrally at the posterior
end of the esophagus. The twisting of the esophagus
is the result of torsion in the veliger stage. Lateral
pouches or sacculations are found between the greater
and lesser folds. They become smaller and finally
disappear as the esophagus curves to the right in the
mid-visceral region (Figure 7).
The paired buccal glands lie along or under the mid¬
esophagus. Their ducts, which overlie the head muscles
and empty into the oral cavity on dorso-lateral folds,
are white and prominent.
The numerous posterior salivary, or esophageal glands
lie on either side of the pharynx dilation and esophagus.
The are conspicuous, small, finger-like processes that
Catherine Gene Walker
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extend out laterally and, in some species, ventrally
around the esophagus. These glands open into tiny
pockets, which in turn are divisions of the lateral
sacculations of the esophageal wall. Like the esophageal
folds, the glands and pharynx dilation appear twisted
as a result of torsion.
The esophagus passes into the proventriculus or
forechamber of the stomach, which opens into the stomach
by way of a contractable aperture encircled by numerous
small folds. The stomach forms a wide loop, encircling
the digestive gland. In sexually mature individuals
the gonad is sometimes visible laterally beyond the
stomach margin.
The digestive gland occupies the central region
of the visceral hump, slightly overlapping the inner
margin of the stomach and almost completely covering
the right lateral pootions. A single digestive gland
janction with the csophaqus.
duct enters the stomach near its prorimalend. The
volume and color of the gland vary somewhat with species
and with the size of the animal.
The hind gut makes a series of four loops before it
empties into the rectum. (Figure 2). Loops 1 and 4
circle clockwise, while Loops 2 and 3 circle counter¬
clockwise. The rectum begins where Loop 4 crosses the
anterior portion of the stomach. Constriction of the
feces into linked pellets occurs in the latter portion
4/3
Catherine Gene Walker
-6
of Loop 4 and the rectum. The pellets are readily broken
up, making them easily washed out of the nuchal cavity
when the animal is splashed. Often if the animal has not
been exposed to water for some time, fecal pellets may
fill both sides of the mantle cavity.
In the comparative study of the gut in species of
Acmaea, differences between species were observed in
the length and placement of the radula sac in the body,
the jaw, the salivary glands, and the gut loops.
LENGTH AND PLACEMENT OF THE RADULA SAC
The radula sac of all species except Acmaea scutum
extends only to the mid-visceral region (Figures3 and 4).
The radula sac of A. scutum passes farther to the left
and extends to the posterior visceral region before
passing anteriorly again (Figure 4). The radula sac
of A. scutum is almost twice the length of the shell,
while in the other species it rarely exceeds 1.5 times
the shell length (Table 1).
THE JAW
For species comparison, the jaw was removed, the
muscle scraped away from the lower side, and the jaw
then examined microscopically. When jaws were mounted
vater
in fluid on slides, the cover slips were slightly prop-
then
ped up to avoid breaking the jawsor bending severely.
Approximately 10 jaws, taken from animals ranging from
small to large, were examined for each species (Figure 5).
Catherine Gene Walker
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The jaw remains the same size, relative to the size of
the animal, as growth occurs. With age, however, the
anterior band gets harder and darker. The median ridges
of the band become more prom-inent, possible as a
result of wear caused by scraping of the radula,
In Figure 5 the jaws of large adult specimens of
the species studied are arranged according to an increase
in the irregularity of the anterior band. Acmaea asmi,
A. limatula, and A. scutum show little or no marking on
the band, and the anterior margin is smooth and unridged.
A. scabra, A. digitalis, and A. paradigitialis have small
ridges in the medial region of the band, causing the
margin to be slightly uneven. In A. insessa, A. pelta,
and Lottia gigantia the anterior band bears a conspicuous
median tooth with smaller ridges running along it. This
characteristic is most apparent in A. pelta, which also
has a darker anterior band. The undulating anterior
border of the anterior band in the jaw of Lottia is
rather distinctive. Species differences in shape of the
lateral wings of the jaw are less apparent, though?
variations occur in wing shape and in the relative size
of the anterior and posterior wings.
ANTERIOR AND POSTERIOR SALIVARY GLANDS
The anterior and posterior salivary glands show
some variation in placement and size in the species
examined. In Acmaea digitalis, A. limatula, and A. scutum
Catherine Gene Walker
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the two buccal or anterior salivary glands extend along
the esophagus, their posterior ends lying on the esopha¬
to the
gus, rear of the posterior salivary glands (Figure 6).
The ducts of the buccal glands of A. pelta, A. scabra,
and A. asmi are shorter and wind back and forth several
times across the head muscles (Figure 7). In these
species the distal extremities of the buccal glands
terminate near the posterior margin of the buccal mass
on either side.
In Acmaea digitalis, A. scabra, and A. limatula
the very numerous posterior salivary glands extend
straight out from the pharynx dilation and anterior
esophagus (Figure 6). In A. pelta and A. scutum
the pharynx dilation is wider than in the above species
and the twist of the esophagus more apparent. (Figure 7).
The glands here are slightly smaller, and curve ventrally
around the foregut. In A. asmi the posterior salivary
glands are very small, and light green in color, while
in the other species they are white. A count of glands
was attempted, but an exact number was difficult to
obtain. The left side of the esophagus has about 65
glands, while the right side has a slightly smaller
number, the number varying somehat with size of the
animal and the species.
LOOPING OF THE GUT
The length and placement of the gut loops in six
species of limpets is shown in Figure 8. Some variation
Catherine Gene Walker
-9
in the exact placement of the loops occurs within the
individual species depending on the size of the animal
and the degree of maturity of the gonad. However, there
is a characteristic placement of the loops in each species.
In Acmaea peltay A. scutum, and A. scabra Loop l circles
farther posteriorly. Loop 2 is considerably smaller
in A. digitalis, A. scabra, and A. asmi. In A. asmi
the anterior portionsof Loops 1 and 2 extend farther
anterior reltive to the stomach. In A. digitalis,
and A. scabra Loop 3 does not lie as far to the left as
in the other species. Dorsoventral thickness of the
visceral mass is difficult to show in the drawings; in
A. limatula and A. scutum, both rather flat species,
the loops lie beside or just beneath one another.
In the other species with taller shells the loops pass
back and forth from ventral to dorsal regions as they
twist through the digestive gland. The digestive tracts
in A.pelta, A. limatula, and A. scutum are somewhat
greater in diameter than those of the other species;
this is a consistent difference, which appears related
to diet but shows up whether the gut is full or empty.
The stomach of A. pelta often contains sizable fragments
of larger algae, and this species has been shown by
Craig (1966) to feed mainly on larger red, brown, and
green algae. The gut in A. limatula, which feeds mainly
on flat encrusting red algae (Eaton, 1966) contains
smaller fragments. The gut contents of A. scutum ob¬
Catherine Gene Walker
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served in the present study resembled those found in
A. limatula. In contrast A. digitalis, A. scabra, and
A. asmi are known to eat microscopic green and blue¬
green algae and diatoms (Castenholz,1961; Fritchman, 1961;
Haven, 1965). The gut contents of these three species
consists at very finely divided material.
Looping of the gut is less complex in the smallest
limpets. In order to determine at what stages the small
limpets develop the adult pattern of intestinal coils,
small limpets, 0.5 - 5.0 mm in shell length, were examined.
Animals 3 to 5 mm long could be identified to species.
They were preserved and dissected ;in the usual way.
Results showed that the digestive tract was present
in essentially the adult condition. Still smaller
individuals (1-2 mm in shell length) probably represent¬
ing Acmaea scabra and A. digitalis were collected in
a small splash pool in the high intertidal zone, which
contained only large A. scabra and A. digitalis.
Minute specimens (0.5 - 2.0 mm in shell length) of
these species and probably A. pelta as well, were also
collected.in the crevices among Mytilus californianus
Conrad 1837, Tetraclita squamosa Darwin, 1854, and
Mitella polymerus (Sowerby, 1833). These tiny limpets
were killed and preserved in 70% alcohol, dehydrated
in an alcohol series (Ehe shells being removed in 95%
alcohol), and cleared in cedar wood oil. The foot and
Catherine Gene Walker
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mantle was removed by dissection, and the animals mounted
on slides in cedar wood oil. The limpets had been
feeding, and the digestive tract was dark and clearly
distinguishable through the remaining more transparenfk
tissues.
The results of these studies are shown in Figures
9 - 11. Limpets 0,5 - 1.5 mm in shell length have a
relatively short stomach and intestine, and intestinal
Loops 1, 2, and 3 are not evident, though there are
twists in the gut. Loop 4 and the rectum are :in the
normal position. Limpets 1.5 - 2.5 mm in length have
Loops 1, 2, and 3 but these are not fully developed
(Figure 12). When the shell reaches 2.5 - 3.5 mm in
length the digestive tract is almost the same as that
in the lrger animals (Figure 13). Placement of the
inner Loops 1, 2, and 3 may be slightly out of regular
orientation, but this displacement is random. The
radula sac is easily seen in its normal posifion.
COELOMIC SYSTEM
The coelomic system consists of four interconnected
cavities in the visceral mass: the right and left kidneys,
the pericardium, and the gonad. The points of inter-
connection lie anteriorly on the right side of the visc¬
eral mass, just behind the muscular wall of the nuchal
cavity (Figure?12).
The right kidney, easily identified by its dark
green to brown color, encircles the whole visceral mass,
Catherine Gene Walker
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with its distal end just posterior to the pericardium.
Internally its surface is quite irregular. The large
right renal-genital pore has thick muscular lips and
is just to the right of the anal opening. The pore on
Acmaea scabra is much larger than that in the other
species, and even exceeds the size of the anus. The
left kidney is much smaller and difficult to distinguish
from the muscular wall separating the pallial and visceral
cavities. It is situated just back of the nuchal cavity,
between the midline and the anus, and overlies part of
the rectum (Figure 12). A. digitalis and A. scabra
both have relatively large left kidneys. The left
renal pore is a narrow slit opening on the anterior
surface of the middle of the kidney (Figure 13). Only
in A. digitalis are there very small bulbous lips on
each side of the slit.
The pericardium occupies the space above the gonad
reoy
in the left dorsal anterior a of the visceral mass.
From it the reno-pericardial canal (Figure 13) crosses
the body from left to right and, as in Lottia gigantea
(see Fisher, 1904), divides just under the left kidney,
one canal going to the left kidney and one under the
rectum to the right kidney.
The gonad is situated in the hollow above the foot
beneath the digestive system. During the breeding
season when it is greatly enlarged it extends up around
the qut. The duct is merely an extension of the thin
3.
4.
Catherine Gene Walker
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epithelium that surrounds the gonad (Figure 13). It
arises on the antero-dorsal wall of the gonad in the
midline and extends to the right to open into the right
kidney. Gametes pass from the gonad to the right kidney,
and leave the kidney through the right renal-genital pore.
SUMMARY
Placement and extent of the radular sac, the form
1.
of the jaw, the arrangement of the salivary glands,
the looping of the gut, and the interconnections of
coelomic derivatives are described and illustrated
for Acmaea: A. asmi, A. digitalis, A. limatula,
A. pelta, A. scabra, A. scutum, A. insessa, A. para-
digitalis. Some notes on Lottia gigantea are included.
The radula of A. scutum is almost twice the length
of its shell, while in the other species the radula
ranges from 1 - 1.5 times the length of the shell.
Limpet jaws vary primarily in the shape and character
of the hard anterior band. The jaws of K. pelta,
A. insessa, and Lottia gigantea bear an anterior
median tooth.
The limpets studied can be separated into two groups
on the basis of the salivary glands. A. digitalis,
A. limatula, and A. scutum.have buccal glands that
extend down the esophagus posterior to the esophgeal
glands, while in the other species they terminate
near the posterior margin of the buccal mass.
45
6.
Catherine Gene Walker
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In A. pelta and A. scutum the posterior salivary
glands are slightly smaller, and curve ventrally
around the foregut, while in the other species
the glands etend straight out from the pharynx
and esophagus.
The pattern of gut loops showa minor but consistent
differences between Acmaea species. Development
of the adult pattern of loops is essentially com¬
pleted before animals reach a shell length of Amm.
The gut tends to be thicker and heavier in species
feeding on larger erect or encrusting algae (A. pelta,
A. limatula, A. scutum) than in species feeding on
films of microscopic algae (A. digitalis, A. scabra
A. asmi).
The coelomic cavities and ducts are described and
diagramed. Both right and left kidneys of A. digitalis
and A. scabra are relatively larger than those of
other Acmaea species.
Aneexcellent paper by Righi (1966), published after
the present study was completed, describes the internal
anatomy of the Brazilian species of Acmaea and provides
illustrations permitting comparisons to be made between
Brazilian and Californian species. Righi also finds that
the shape of the jaw and the looping of the gut provide
means of distinguishing Acmaea species.
48
Catherine Gene Walker
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ACKNOWLEDGMENTS
My sincere thanks go to Dr. Donald Abbott for his
encouragement and guidance throughout this project. Thanks
also are extended to the staff of Hopkins Marine Station.
This work was made possible by Grant G4806 from the
Undergraduate Research Participation Program of the
National Science Foundation.
42
Catherine Gene Walker
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LITERATURE CITED
Castenholz, Richard W.
1961. The effect of grazing on marine littoral
diatom populations. Ecology 42 (4): 783-794, 6 figs.
Craig, Peter C.
1966. The activity pattern and food habits of
the limpet, Acmaea pelta. The Veliger
Eaton,
Charles M.
1966. The Activity and food of the file limpet,
Acmaea limatula. The Veliger
Fisher, Walter K.
1904. The anatomy of Lottia gigantea. Zool.
Jahrb., Anat. 20 (1): 1-66, 13 figs., pls. 1-4.
Fretter, Vera, and Alastair Graham
1962. British Prosobranch Molluscs. The Ray
Society, London. 1-xvi + 755 pp., illus.
Fritchman, Harry K.
1960. Acmaea paradigitalis sp. nov. (Acmaeidae,
Gastropoda). The Veliger 2 (3): 53-57, pls. 9-12.
Fritchman, Harry K.
1961. A study of the reproductive cycle in the
California Acmaeidae (Gastropoda). The Veliger:
Part I, 3 (3): 57-63, pl. 10. Part II, 3 (4):
pls. (5-17.
95-101, Part III, 4 (1): 41-47, pls. 9-14.
123
Catherine Gene Walker
-17-
Haven, Stoner B.
1965. Field experiments on competition between two
ecologically similar intertidal gastropods. Bull.
Ecol. Soc. Amer. 46 (4): 160.
G.
Righi,
1966. On the Brazilian species in the Acmaea subrugosa
complex (Gastropoda: Prosobranchia: Patellacea).
Malacologia 4 (2): 269-295, 27 figs.
Runham, N. W.
1963. A study of the replacement mechanism of the
pulmonate radula. Quart. Jour. Micros. Sci. 104 (2):
271-277, 3 figs.
Test, Avery R. (Grant)
1945. Ecology of California Acmaea. Ecology 26 (4):
395-405.
Test, Avery R. (Grant)
1946. Speciation in limpets of the genus Acmaea.
Contrib. Lab. Vert. Zool., Univ. Michigan 31: 1-24
42
SPECIES
A. limatula
A. insessa
A. digitalis
A. paradigitalis
A. scabra
A. asmi
A. pelta
Lottia gigantea
scutum
NUMBER OF
SPECIMENS
EXAMINED
10
10
10
10
10
10
10
10
14
-18
TABLE 1
SIZE RANGE
SHELL LENGTH
cm.
2.0 - 3.5
1.5 - 2.0
1.5 - 2.5
1.0 - 2.0
1.0 - 2.5
0.5 - 2.5
1.3 - 3.5
3.0 - 5.6
1.5 - 4.0
Catherine Gene Walker
RADULA LENGTH
RATIOMOF SHELL LENGTH
RANGE
MEAN
o.90 - 1.29
1.06
0.97 - 1.33
1.07
0.90 - 1.25
1.13
1.00 - 1.40
1.19
1.00 - 1.40
1.20
1.06 - 1.37
1.23
1.06 - 1.50
1.24
1.07 - 1.58
1.29
1.71 - 2.00
1.90
2
Catherine Gene Walker
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CAPTIONS
Figure 1:
Generalized dorsal view of an Acmaea with shell and mantle
removed: AN - anus, GPT - cephalic tentacles, CT - ctenidium,
DG - digestive gland, E - eyespot, ET - foot, GN - gonad,
RCT - rectum, RS - radula sac, SM - shell muscle, ST - stomach.
Figure 2:
Generalized dorsal view of the digestive tract of an Acmaea
spe with the dorsal body wall, kidneys, gonad, digestive
gland, and pericardium removed: AN - anus, DGD - digestive
gland duct, ES - esophagus, J - jaw, RRO - Proventriculus¬
RCT - Rectum, RS - radula sac.
Figure 3:
Dorsal view showing the placement of the radula sac in the
visceral cavity of Acmaea limatula (shell length - 2.5cm.;
ratio of radula lenghh: shell length - 1.11). Placement
of the sac here is similar to that in A. pelta, A. scabra,
A. digitalis, and A. asmi. ES - esophagus, RC - Radula
caecum, RS - radula sac, ST - stomach.
Figure 4:
Dorsal view showing the placement of the radularsac in
the visceral cavity of Acmaea scutum (shell length - 2.5cm;
ratio of radula length: shell length 7 1.9). ES - esophagus,
RC - radula caecum, RS - radula sac, ST - stomach.
Figure 5:
Dorsal viewsof the jaws of large adult limpets. The jaws
are partially flattened out on slides and drawn with a
camera lucida. Dark areas represent the most opaque areas.
Ke
Catherine Gene Walker
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Figure 6:
Dorsal view of the anterior end of Acmaea digitalis, showing
the location of the anterior (buccal) and posterior salivary
glands. Semi-diagrammatic, based on 15 adult individuals.
BG - buccal gland, BGD - buccal gland duct, ES - espphagua,
GN - gonad, J - jaw, PD - pharynx dilation, PSG - posterior
salivary glands, RS - Radula sac, ST - stomach.
Figure 7:
Dorsal view of the anterior end of Acmaea pelta, showing
the location of the anterior (buccal) and posterior
salivary glands. Semi-diagrammatic, based on 15 adult
individuals. BG - buccal gland, BGD - buccal gland duct,
GF - Greater folds, J - jaw, LF - lesser folds, PD -
pharynx dilation, PSG - posterior salivary glands,
RS - radula sac, SAC - sacculations.
Figure 8:
Diagrams of the stomach, intestine, and rectum of adult
individuals of six species of Acmaea,based on dissections
of 25 - 30 animals of each species. Exact placement of
the loops is subject to slight variation, within each species;
the diagrams show the typical condition in large adults.
RCT - rectum, ST - stomach.
Figures99, 10, 11:
Generalized diagrams of Acmaea digitalig and A. scabra,
showing the development of the digestive tract in dorsal
view. RCT - rectum, ST - stomach
42
Catherine Gene Walker
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Figure 12.
Generalized dorsal view of the coelomic system in Acmaea,
with the dorsal body wall, digestive system, and posterior
te
wall of, nuchal cavity removed. AN - anus, GN - gonad,
LK - left kidney, P - pericardium, RK - right kidney,
RRP - right renal pore.
Figure 13:
Enlarged view of the right upper corner of Figure 12,
showing the interconnection of the coelomic cavities.
Kidneys and anus open into the nuchal cavityl. AN - anus,
CT - ctenicium, GN - gonad, GND - gonad duct, LRP-left
renal pore, PRCr pericardial renal canal, RK - right kidney,
RRP - right renal pore.
Permanent address:

-22-
FOOTNOTES
43
Catherine Gene Walker
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