SHOWEN: DEFENSE RESPONSE OF ARCTONOE VITTATA
INTRODUCTION:
The keyhole limpet Diadora aspera (Eschscholtz, 1833) is
one of the many hosts of the scaleworm Arconoe vittata.
(Grube, 1955). Margolin (1964) found that Diadora raises
its membranous, frilled mantle, virtually covering its
shell in response to contact with a predatory seastar
or upon exposure to seawater in which a seastar had been
kept.
Dimock and Dimock (1972) report that A. vittata will bite
the tube feet of various seastars, including Pisaste:
ochraceus (Brandt, 1835) following seastar-limpet con-
tact and initiation of the mantle response. They also
present evidence that no substance released from Diadora
was involved in eliciting the response from A. vittata
and that a worm isolated from its host would not bite
a starfish. Their paper was a brief note based on small
sample size. I here further elucidate the mechanism of
this behavior.
MATERIALS AND METHODS:
Diadora aspera, two to five cm in length, with commensal
ctonoe vittata were collected during April and May of
1976 from a submerged rocky outcropping known as the
Pinnacles (36°33' North by 121°58' West) in 70 to 95
feet of water. Intertidal Pisaster ochraceus were used
as the test animals. Animals were kept in aquaria with
running sea water at Hopkins Marine Station, Pacific
Grove, California. Due to the difficulty in collecting
numbers of 4 vittata most worms were used in more than
one experiment.
Basic Experiment: D. aspera with commensal worms were
placed on glass and observed from the underside, rather
than in enameled trays from above as in Dimock and
Dimocks work. An arm of a Pisaster was brought into
SHOWEN: DEFENSE RESPONSE OF ARCTONOE VITTATA
contact with the edge of the Diadora shell. Often
the starfish would move itself upon the glass, cover¬
ing a large part of the shell. Muring the ten minute
trial period notes were taken on the movements of the
starfish, the host and the commensal.
Starfish Water Experiment: To determine if either the
host's mantle response or water which had contacted
Pisaster could cause a worm to search without direct
contact of the starfish to the limpet, two starfish
were introduced to test aquaria but not permitted to
contact the host. The animals were observed for ten
minutes.
"Diadora Juice" Experiments: Five limpets and an isolated
worm were placed in a small plastic tray of sea water
and a seastar was touched to the worm. Observation
was for ten minutes in each of three trials.
Additionally, mucus and seawater from the mantle cavity
of a Diadora in which a mantle response had been
previously elicited by a starfish was pipetted onto an
isolated Arctonoe in contact with a seastar. The
worms were observed for three minutes in each of five
trials.
MgCl. Experiment: In order to test for the necessity
of the physical movement of the mantle response for
biting to occur limpets with their worms removed
were placed in isotonic Mgcly solution, an anaesthetic,
for several hours. The relaxed Diadora were then
placed upside down in aquaria and held in place with
a lump of clay. The worms were then returned to the
hosts and after the worm was settled a starfish was
placed in contact with it. The observation period was
ten minutes in each of three trials.
SHOWEN: DEFENSE RESPONSE OF ARCTONOE VITTATA
Gelatin Groove Experiment: To test for the necessity of
the Diadora's presence for biting to occur an arm of
a starfish was touched to the anterior portion of an
Arctonoe placed in a shallow groove in fresh, firm
g dry gelatin in 100 ml seawater). The groove was
roughly "worm sized" in all dimensions, so as to allow
the worm to fit in snuggly. Tests were scored only it the
worm remained in the groove for the ten minte trial
period. As a control isolated worms were tested against
a starfish on a gelatin surface without a groove. The
observation period for the control experiments was also
ten minutes for each of five trials.
Palps Excised Experiment: Worms without palps were
tested using the "Basic Experiment" procedure.
RESULT
The Arctonoe vittata were variable in their markings.
One type had the posterior edge of the first pair of
elytra marked with a black or brown band, whereas the
other type had no such marking. Except for this marking,
the worms were white or cream colored. None of the worms
had the dark band across segments seven and eight
commonly associated with the species yet prostomial and
parapodial characteristics are those of A. vittata.
Eight of 17 marked worms were observed to bite whereas
only one of 12 unmarked bit. The difference is signi¬
ficant at the .025 level according to the G-test.
Prior to the introduction of the seastar the worm was
generally motionless in the mantle cavity, with its
dark tipped palps usually retracted but occasionally
extended and waving. After introduction of the star-
fish the Arctonoe would remain motionless until the
onset of the mantle response. The first response of the
worm noted was waving of its palps and the anterior
portion of its body. It would then emerge from beneath
SHOWEN: DEFENSE RESPONSE OF ARCTONOE VITTAT
the shell and display the searching behavior described
by Dimock and Dimock. Nine worms never showed any
search activity at all. While a few worms moved
directly towards the tube feet, as described by Dimock
and Dimock, many seemed to be searching randomly.
Twelve worms showed search behavior but never contacted
a starfish and bit. Only if the starfish was within
a centimeter or two was the worm able to pinpoint the
point of tube foot contact. Nine of the worms, upon
contact with a tube foot, ran their palps along the
tube foot and everted their proboscis and bit, often
holding on to the tube foot for several seconds.
All data following applies to marked worms only.
Starfish Water Experiment: The three limpets displayed
the mantle response when near but not touching the
Pisasters. All the worms displayed search behavior.
Four worms with palps removed also showed searching
behavior using the same test procedure. Additionally,
this searching behavior was observed at least ten times
when water in which starfish had been kept was allowed
to flow into aquaria containg Diadora with commensal
worms.
"Diadora Juice" Experiment: In five experiments in which
fluid from the mantle cavity was applied to an isolated
worm in contact with a Pisaster, no aggressive behavior
occurred and no increase in activity was noted. The worm
often remained among or next to the tube feet.
In three trials in which an isolated Arctonoe vittata
was placed in contact with a Pisaster in seawater with
five disturbed Diadora, no searching or aggressive
behavior by any worm occurred.
MgCl, Experiment: Arctonoe returned to Diadora rendered
limp from MgCly treatment behaved normally, although
they were not as protected as in a normal limpet.
TTAT
SHOWEN:DEFENSE RESPONSE OF ARCTONOE
When a starfish was touched to the limpet but not the
worm, the Arctonoe always remained inactive. Only when
the tube feet actually contacted the prostomial region
did the worm become aroused and exhibit searching be-
havior. This resulted in biting in three of the six
worms tested.
Gelatin Groove Experiment: The response of Arctonoe
in a gelatin groove was similar to their behavior on
a limpet treated with Mgolø solution.
Again, in six trials the worms never turned in the di-
rection of a tube foot, stretched out towards a tube foot,
or bit until the prostomial region was touched with
a tube foot. Six worms remained in the gelatin groove
for ten minutes; three of them bit. Approximately two
thirds of the worms left the groove before ten minutes.
Worms did not remain in gelatin preparations more than
several hours old, possibly due to the presence of
increased numbers of microorganisms.
Palps Excised Experiment: Worms with palps removed
behaved like normal worms with one important exception.
Two of seven
ctonoe tested made attempts at biting;
both of them missed the tube feet. This phenomenon was
also observed informally on three other occasions. No
worms missing palps was ever observed to successfully
bite a tube foot.
DISCUSSION:
The fact that Arctone bearing a dark band bite signi-
cantly more than unmarked worms indicates the two
sympatric groups vary in more than one genetic trait.
If this indicates gene isolation between the forms is
not yet known.
Dimock and Dimock indicated the presence of a Pisaster
is insufficient to cause biting in an isolated worm.
Some stimulus, associated with the presence of the
host is required.
That worms do not search on MgClz treated limpets
indicates that mere presence of the host and starfish
m
SHOWEN:DEFENSE RESPONSE OF ARCTONOE VITTATA
is not adequate to elicit searching. Some cue from the
iadora must be missing, either a physical movement, a
chemical released during the mantle response, or a
chemical the effects of which are negated by Mgcl2.
It was observed that Arctonoe on normal limpets either
isaster
in contact with or merely in the same tank with
will search only after initiation of the mantle
response. This confirms that mere presence of a seastar
in the environment will not elicit searching, and
indicates that some aspect of the mantle response must
initiate search behavior. Dimock and Dimock did not
observe that worms searched on limpets exposed to
seawater in which starfish had been kept. However,
Margolin (1964) reports that 100% of Diadora tested
gave the mantle response in reaction to seastar water
whereas only one of ten limpets did so in the Dimocks
experiment.
That worms do not become aroused either in the presence
of disturbed Diadora or upon direct application of mucus
from a disturbed limpet indicate that: 1. No water
soluble substance released from Diadora during the
mantle response or insoluble substance in the mucus
is responsible for initiating searchinging. 2. There is
no chemical whose effects are negated by Mgcl,. The
physical movement of the mantle is necessarry and
sufficient to elicit searching.
That worms will bite on MgCl, treated limpet or in a
gelatin groove once contacted by a tube foot indicates
that the worm must merely be in a groove and directly
contact a starfish for biting to occur.
Experiments involving worms without palps dekmonstrate
palps are not needed for detection of or reaction to
a Pisaster but that they are required for proper
coordination of the bite.
Biting then results from a two part behavior; searching
C
ABCT
FNC
SHOWEN:DEFENSE RESPONSE OF ARCTONOE VITTATA
in response to the physical movement of the mantle
followed by biting in reponse to position in a groove
and contact with a starfish.
SUMMARY:
1. Commensal Arctonoe vittata marked with a dark band
ter ochraceus significantly
were shown to bite I
more than unmarked worms on host Diadora as
2. Arctonoe were shown to search in response to the
physical movement of the mantle reponse.
3. Arctonoe were found to bite, once aroused, if they
were situated in a groove and contacted a tube foot.
4. Worms with palps removed were found to miss the
tube foot when attempting tobite.
ACKNOWLEDGEMENTS: Many thanks to Dr. Robin Burnett for
much help in thinking about this project, to Jim Watanabe
for assistance in collecting, and to the entire faculty
and staff of Hopkins Marine Station for making this
project possible.
e
SHOWEN: DEFENSE RESPONSE OF ARCTONOE VITTATA
LITERATURE CITED:
Dimock, Ronald V. and Joyce G.
1969 A possible "defense" response in a commensal
polychaete. The Veliger 12:65-68
Margolin, Abraham Stanley
1964. The mantle response of Diadora aspera.
Animal Behavior 12:187-194
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