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Introduction
The habits and habitats of Cyanoplax dentiens (Gould, 1846)
have received little attention. Those papers that have
investigated C. dentiens (Heath, 1905; Berry, 1917; Berry, 1948)
indicate a far ranging intertidal habitat for it but give no
mention of interactions between it and other organisms.
Presented is a report on a finding that this small (2 1 cm.)
chiton Cyanoplax dentiens (Light, 1964; Smith, 1974) is often
found under the moderately large (=40 cm.) chiton Nuttallina
californica (Reeve, 1847). Field and laboratory studies show
that: a) this association is not random; b) C. dentiens is
negatively phototaxic; c) C. dentiens can actively crawl under
Nuttallina; and d) C. dentiens can detect and seek out Nuttallina.
Field Studies
A total of over 100 Nuttallina from Carmel Beach, Carmel,
California; Point Pinos, Pacific Grove, California; and Mussel
Point, Pacific Grove, California, were removed; only under those
Nuttallina from Point Pinos were many Cyanoplax dentiens found.
The association between Nuttallina and C. dentiens was restricted
to vertical and angled rock faces with moderate to little light
exposure in the mid-zone of the Nuttallina range (3-4 foot
tidal height).
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presence and direction of a nearby "host" Nuttallina since the
low field density of the latter would make chance encounter
an unlikely event. In order to test for the ability to detect
chemical cues carried down a flow of water from a Nuttallina
a simple Y-maze experimented was conducted. Three 12-hour
trials were run using ten fresh Cyanoplax starting at the base
of the Y for each trial. At the top of one arm of the Y was
placed a Nuttallina and a glass vial was placed at the top of
the other arm in order to approximately match any possible
turbulence in the fresh sea water which was allowed to flow
equally down each arm towards the base (Fig. 1). Pooled
results indicated non-random movement (chi-square test; p«.01).
with 18 C. dentiens moving over 1 cm. toward the Nuttallina
and 3 over 1 cm. away. A control without a Nuttallina showed
random movement.
A phototaxic test of C. dentiens was run in a wooden
fepaln
tray with
—1 a 200-watt light bulb at one end, ad a
gente tio of waret peedide ro e ig-dat axs.
Fifteen C. dentiens were placed along the mid-line of the tray
and tested for 12 hours. Fourteen went 2 cm. or more away
from the light, indicating negative phototaxis.
On three occasions Cyanoplax dentiens kept in finger bowls
with Nuttallina were observed to move under their "host". The
Nuttallina neither conspicuously lifted its girdle to accomodate
the Cyanoplax nor did it make an obvious attempt to avoid the
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Over 100 Cyanoplax dentiens were collected from Point
Individual intertidal rocks were exhaustively examined and all C.
dentiens en¬
Pinos.Only 10% of these were not tound under Nuttallina,
Pountered were
frequency well below that expected for a chance association.
removed.
Approximately 25 Acmaea and 10 chitons of species other than
Nuttallina were investigated, but no C. dentiens were found
under any of these animals.
A 12-hour night watch was conducted of 5 Nuttallina, 3
with Cyanoplax dentiens naturally occurring and 2 with C.
dentiens introduced under them. The positions of all chitons
had been previously mapped out and marked two days prior to
the watch. A red light was used at regular one-haur intervals
to observe the chitons and the distance they had travelled.
To be able to make regular readings even at high tide, the
investigator wore a wet suit and face-mask. During the watch
3 Nuttallina left their locations; 2 returned to take up their
original position. No C. dentiens moved during the watch
despite the fact that those exposed by the moving Nuttallina
encountered heavy wave shock. Dessication may play a larger
role in the association than wave shock since Nuttallina move
primarily at night (Moore, 1974), a time when dessication rates
are low.
Laboratory Studies
It seemed likely that Cyanoplax dentiens could detect the
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smaller chiton. Once under the Nuttallina, the Cyanoplax
oriented lengthwise along the pallial groove, but showed no
preference to facing anteriorly or posteriorly relative to the
"host".
Discussion
Cyanoplax dentiens, in using Nuttallina californica as
a microhabitat, is benefited in several ways: protection
against dessication,  sunlight, predators and against
other physical parameters. C. dentiens further restricts its
habitat by not locating itself under either those Muttallina
outside of the mid-zone of the Nuttallina range or those
exposed to stronger light; the latter restriction perhaps a
afarent
result of its,negative phototaxis.
Cyanoplax dentiens can seek out and detect Nuttallina,
as the Y-maze test indicated, presumably using a chemical cue.
This ability implies coevolution has occurred.
Summary
1) Cyanoplax dentiens was found underneath Juttallina
californica, along its pallial groove.
2) The association was restricted primarily to those
Nuttallina on a shady vertical or angled rock face in the
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mid-zone of the Nuttallina range.
to be negatively phototaxic.
3) C. dentiens
4) C. dentiens possibly uses Nuttallina as its micro-
habitat for purposes of protection against dessication, harsh
etc.
sunlight, predators,
5) C. dentiens was found capable of detecting and
seeking out Nuttallina californica.
e
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Acknowledgments
I wish to thank Dr. Robin Burnett for his advice and
most of all Katherine for her encouragement and great
assistance in the realization of this paper.
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Literature
Berry, Stillman
Notes on West American chitons. Proc. Calif.
1917.
Acad. Sci. (4)7(10):229-248; 4 figs.
Berry, Stillman
Two misunderstood West American chitons.
1948.
Leaflets in Malacol 1(4):13-16.
Heath, Harold
The breeding habits of chitons of the California
1905.
coast. Zool. Anz. 29(12):390-393 (19 September 1905)
Light, Sol Felty
1964. Intertidal invertebrates of the central California
coast. Revised by Ralph I. Smith, Frank A. Pitelka,
Donald P. Abbott, and Frances M. Weesner. xiv + 446 pp.;
138 figs. Berkeley, Calif. (Univ. of Calif. Press)
Moore, Michael Matthew, Jr.
1975. Foraging of the western gull Larus occidentalis
and its impact on the chiton Nuttallina californica. The
Veliger.
Smith, Allyn G.
1974. Personal communication on the identification of
Cyanoplax dentiens.
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Fig. 1
Y-maze test. Flowing current in a tray was equally divided
by Y-structure (A) and carried past the ten Cyanoplax dentiens
(B). Twelve hours were allowed for movement of the C.
dentiens toward either the Nuttallina californica (C) or the
glass vial (D).
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