Linsenmeyer
Attachment of Chitons
INTRODUCTION
According to Arey and Crozier (1919), the mechanism
by which Polyplacophora attach themselves to surfaces is
suction, primarily from the mantle. Hoffman (1931)
comments that the role of the ventral mantle and the foot
are of equal importance in fastening to surfaces. Detailed
research on this subject, however, is lacking.
This investigation was designed to determine the
forces required to remove several species of Polyplacophora
from various surfaces, and to elucidate the mechanism by
which they resist removal.
MATERIALS AND METHODS
Mopalia lignosa (Gould, 1846), Mopalia muscosa (Gould,
1846), Nuttalina californica (Reeve, 1847), Katharina
tunicata (Wood, 1815), and Stenoplax heathiana (Berry,
1946) were collected intertidally off the Monterey
Peninsula in California in April and May, 1974. After
collection, undamaged chitons were held in running sea
water aquaria until tested. Chitons were used within
four days of collection and each animal was used in only
one trial.
Prior to testing, chitons were allowed to attach to
the test surface for a period of two hours. The device
sketched in Figure 1 was used to determine the resistance
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Attachment of Chitons
to removal by a force parallel to the surface. Aproximately
three grams were added to the container every two seconds
until the animal broke free of the surface. The device
had a mechanical advantage of two so that the force
required to remove the chiton was taken as twice the
weight of the container.
To determine resistance to removal by a force
perpendicular to the surface, a cloth-backed picture
hanger was glued to the dried plates of an animal
(using the contact glue "ZIP GRIP" 10, Devcon Co.,
Danvers, Mass.), and connected by a string to the device
illustrated in Figure 2. Weights were added at the rate
of three grams every two seconds.
Following each test, the area of the foot and the
total area of the ventral surface were determined by
placing the chiton on a transparent grid. Resistance to
removal is expressd as grams per square centimeter of
foot area, since the foot proved to be the primary site
of attachment.
The relation between roughness of the surface to
which the chiton was attached and resistance to removal
was also determined. Tests were conducted using chitons
attached to smooth glass or Plexiglas, #120 waterproof
emery cloth having an average grit size of 120 u and flat
natural granite.
In order to evaluate the role of reduced atmospheric
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Attachment of Chitons
pressure (suction) under the foot as a method of attachment,
individual Mopalia muscosa, attached to Plexiglas plates,
were placed in a vacuum desiccating jar. Piano wire,
attached to the glued hook on the animal, exeited the
jar through a small hole and was connected to the device
illustrated in Figure 2. Tests were run at atmospheric
pressure and under vacuums of 127 and 380 mm of mercury
below atmospheric pressure.
Additionally, chitons were allowed to settle on
substrates with varying pore size: fritted glass with a
pore diameter of less than 15 u, a 1 mm mesh wire
screen, and Plexiglas containing numerous 3 m diameter
holes. Their ability to cling, after two hours was tested.
RESULTS AND DISCUSSION
Figure 3 shows the resistance of chitons to removal
by forces parallel to a Plexiglas surface, in g/cm of
foot surface, for each species. Nuttallina, which
inhabits rocks subject to heavy surf, exhibited a mean
resistance to removal of 237 g/cm. This was more than
double the resisting force of the three species occupying
the most protected habitats: the two under-rock species,
Stenoplax heathiana and Mopalia lignosa, had mean values
of 64 and 94 g/cm respectively, and Mopalia muscosa,
found on the top surface of protected roacks, had a mean
value of 112 g/cm. Katharina tunicata, which, like
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Attachment of Chitons
Linsenmeyer
Nuttallina, occupies a surf-exposed habitat, had a
comparatively high mean resistance to removal of 146
g/cm. Thus, the resisting force had a direct adaptive
relationship to the habitat occupied by each of the species.
It was observed in all species that the plates and
mantle were forcefully displaced as the loading increased,
while the foot remained fixed. This strongly implies that
the foot plays the major role in attachment.
The lateral forces required to remove Mopalia muscosa
from the three types of surfaces are shown in Figure 4.
Mopalia muscosa had a mean resistance of 112 g/cm
when settled on Plexiglas, 144 g/cm when on #120 emery
cloth and 223 g/cm when on granite. The animals had a
mean resistance to a vertical (lifting) force of 82 g/cm
on natural rock. Thus substrate roughness had a significant
effect on the resistance to detachment by forces both
lateral to and normal to the attachment surface. During
the tests using forces normal to the surface, the plates
and mantle lifted off the surface by as much as 5 mm with¬
out detachment of the foot, again implicating the foot
as the organ of attachment.
No significant differences were detected in the
resistance of Mopalia muscosa to lifting forces applied
at atmospheric pressure and under veuums of 127 and 380
mm of mercury below atmospheric pressure (Figure 5).
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Attachment of Chitons
Chitons could clearly attach to porous glass, wire
screen, and Plexiglas with 3 mm holes. This result also
argutes against suction as a major factor involved in
the resistance of chitons to removal. A chiton on the
3 mm thick Plexiglas with 3 mm holes passed part of its
foot through a hole and expanded it on the opposite side.
providing a mechanical wedging which held the chiton to
the surface. Similarly, portions of the chiton's foot
penetrated the wire screen and expanded on the opposite
side.
When chitons were detached from smooth surfaces, a
relatively insoluble mucus-like residue (hereafter "mucus")
the shape of the chiton's foot remained on the surface.
The chiton's resistance to removal from such smooth
surfaces may be largely due to the adhesive effect of the
mucus they secrete.
It appears that on rough surfaces, the bonding of
chitons to the surface is partially adhesive, due to
mucus, and partially mechanical as the foot conforms
well to surface irregularities. Furthermore, the foot
appears to be the sole organ of attachment.
SUMMARY
1. The lateral force required to dislodge the chitons
Mopalia lignosa, Mopalia muscosa, Nuttallina californica,
Katharina tunicata, and Stenoplax heathiana was directly
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Linsenmeyer
Attachment of Chitons
related to the degree of exposure to wave action in the
habitat of each species.
2. The rougher the surface to which a chiton was attached,
the greater the force required to remove the specimens
from the surface.
3. The foot plays the major role in attachment by secreting
an adhesive mucus material and by mechanically conforming
to surface irregularities with its tissue.
4. Suction does not appear to play a major role in the
attachment of species tested.
ACKNOWLEDGMENTS
I wish to express my appreciation for the help and
encouragement received from the faculty and staff of
Hopkins Marine Station. Special thanks to Dr. Gilmartin,
my advisor, for his time and many helpful suggestions
throughout this study.
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Attachment of Chitons
LITERATURE CITED
Arey, Leslie B. and W. J. Crozier
1919. The sensory responses of Chiton. Journ. exp.
Zool. 29 (2): 157-260; 14 figs.
(October 1919)
Hoffmann, H.
1931. Amphineura und Scaphopoda. H. G. Bronn (ed.).
Klassen und Ordnungen des Thier-reichs. Vol. 3.
Abt. 1.
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Attachment of Chitons
FIGURE CAPTIONS
Figure 1
Device used to determine resistance to removal by a force
parallel to the attachment surface.
Figure 2
Device used to determine resistance to removal by a force
perpendicular to the attachment surface.
Figure 3
A comparison of the lateral force required to detach the
five species of Polyplacophora in relation to the degree
of wave action to which they are normally exposed. Bar
graphs show mean and standard deviation.
Figure 4
The lateral force required to detach Mopalia muscosa from
various substrata.
Bar graphs show mean and standard
deviation.
Figure 5
The vertical lifting force required to detach Mopalia muscosa
from a Plexiglas plate at atmospheric pressure and at vacuums
of 127 and 380 mm of mercury below atmospheric pressure.
Bar graphs depict mean and standard deviation.
page 9
container
for
weights
pulley



lever
2
chiton
FIG
V
20 em
Linsenmeet
container
for
weights



pulleys

—

20 cm
——1


chiton
FlG. 2
Liisenmeget
C
.
X- 237
N= 15
S.D.- 61
X-146
N= 12
5.).= 37
X=112
N- 44
5).- 49
X- 94
X- 64
N= 31
N= 8
S). = 29 5.d.- 27
3
52
Rock Exposed Rock
Under Rock
46111
F16 3
Unsenneet
.. ..1...r
200
3 100
X=112
N=94
S.D.-49
Glass
X-144
N=2
S.D.=56
4120
Substratum
FIG
X=223
N=6
S.D.=69
Rock

iasenmeg
—
50
X-87
=13
S.D.=20
X-82
N=9
S.D.=25

380
127
Vacuum (mm of Hg)
FIG 5
—,
X=9.
N=8
S.D.=43
nsennger