Ophiodromus behavior
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INTRODUCTION
Experimental research on commensal relationships in
polychaetes has been largely limited to studies on host
specificity and recognition in the families Hesionidae
and Polynoidae (Davenport, 1950, 1953; Davenport, et. al.,
1960; Davenport and Hickok, 1951, 1957;Bartel and Davenport,
1956; Hickok and Davenport, 1957). Much of this work has
been devoted to the facultative commensal Ophiodromus
pugettensis (Johnson) [-Podarke pugettensis]. Members
of this species can be found free-living on wharf pilings
and on mud flats (Bartel and Davenport, 1956;Reish, 1961)
and as commensals on several Asteroid species including
Luidia foliata Grube (Hickok and Davenport, 1957) and
Patiria miniata Brandt (Bartel and Davenport, 1956).
A single field study by Lande and Reish (1968) in
southern California demonstrated the seasonal occurrence
of O. pugettensis on P. miniata, with highs occurring in
the winter and lows in the summer months. Commensal pop-
ulations on Patiria were also shown to fluctuate and vary
inversely with water temperature. Laboratory studies
concerning the behavior of the commensal on the host,
however, represent merely casual observations and the
nature of this relationship has only received speculation.
The purpose of this study, therefore, was to examine more
thoroughly 0. pugettensis on P. miniata, both in the field and
in the laboratory, in an effort to elucidate the commensal¬
host behavioral interactions. Observational notes on the
commensal itself are also included.
Ophiodromus
behavior
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M. Serences
FIELD STUDIES
MATERIALS and METHODS
Field studies on Ophiodromus pugettensis were made
over a six week period in April and May 1976 at Hopkins
Marine Station, Pacific Grove, California. Forty-eight
seastars were tagged, measured and the number of commensals
per seastar recorded at a depth of approximately 30 feet
using SCUBA on April 20, 1976. Three subsequent dives
were made on April 21, May 7 and May 26, and the number
of commensals per seastar counted on each occasion.
The seastars were marked using numbered plastic
laundry tags which were shot approximately 1 cm deep
into the aboral surface of the seastar. No permanent
injuries were sustained by the seastars using this
method. Measurements to the nearest millimeter were
made of the seastars from the tip of the longest ray to
the opposite web.
In addition, fifteen seastars with a total of 75
worms were collected on May 12 on SCUBA at a depth of
25 feet. Thirty-one seastars with a total of 111 worms
were collected one week later skin diving at a depth of
20 feet approximately 25 feet towards shore from the
previous site. Two weeks later seastars were collected
on SCUBA from both areas; fourteen with 38 worms from the
first area and thirteen with 41 worms from the second.
The seastars were collected and later placed in an
aquarium for from one to four hours. The commensals were
Ophiodromus behavior
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M. Serences
then removed and placed in a glass dish filled with salt
water. Measurements, to the nearest millimeter, were
made after approximately ten minutes when the initial
contraction response had subsided.

RESULT
Results for the field studies are summarized in
Figures 1 and 2 and Tables 1 and 2. Figure 1 plots
the number of commensals per host versus average size
of P. miniata indicating an increase in commensal pop-
ulations with increasing host size. Figure 2 summarizes
the data on number of commensals per host versus frequency
of occurrence. The index of dispersion for sample size 35
is 54.386 (PK.025) indicating clumping. A significant
difference (P£.05) (X2 test, N-2 degrees of freedom) from
this and a Poisson distribution is apparent. And, comparing
expected versus observed values, a substantially higher
occurrence of starfish without worms than expected is noted.
Table 1 records changes in commensal populations over
time for dive dates. The number fluctuations indicate
that the commensals commonly move on and off of Patiria.
It should be noted here that large 0. pugettensis were
rarely noted in the field aborally on P. miniata. Table
2 lists the size range of the commensalscollected, area,
date, sample size, mean, standard deviation and level of
significance between the two areas sampled. Also included
are size increases (mm/week) and corresponding levels of
Ophiodromus behavior
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M. Serences
significance for similar area populations. Significant
size and growth rate increases among 0. pugettensis as one
moves from subtidal to intertidal areas is indicated.
LABORATORY EXPERIMENT!
T
MATERIALS and METHODS
P. miniata with commensals were collected both
intertidally and subtidally off Hopkins Marine Station,
Studies were conducted over a six week period during
April and May 1976.
Specimens were maintained in 40 liter salt water
aquaria with circulating unfiltered sea water averaging
1° C above local water temperatures. To prevent loss
of worms drainage holes were covered with fine mesh
netting. Movement of the seastars and commensals was
unrestricted except when isolation was necessary. Plastic
containers 28x22x13 cm in which sea water could be cir¬
culated were then used. The following experiments were
conducted altering the system in each case as described.
Experiment 1--To determine whether commensals will
colonize hosts in the laboratory, a Patiria with ten
O. pugettensis was placed in a plastic tank with a con-
specific from which commensals had been removed. Eight
Ophiodromus were then introduced into the center of the
tank. The number of worms per seastar were counted at
irregular intervals over a period of 49 hours. Counts
were made directly through the glass when possible but
Ophiodromus behavior
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M. Serences
when commensals were obscured from view, seastars were
removed and the number of worms counted outside the tank.
Replacement in the tank was made as close as possible to
the original position.
The results are diagramed in Figure 3. Two worms were
without hosts at the conclusion of the experiment. Initially,
six out of eight worms migrated to the host lacking commensals
implying preferential migration as well as dispersal of
O. pugettensis.
Experiment 2—-To discern whether field distributions of
O. pugettensis on P. miniata could be replicated in the
laboratory over a short time period, seventeen Patiria
lacking commensals were added to an aquarium containing
two conspecifics each with eighteen Ophiodromus. Seastars
were removed after five days and the number of commensals
per host recorded.
Results are summarized in Figure 4. Two Patiria
were without commensals following the experimental period.
The index of dispersion for sample size 19 is 23.18 (P2.4)
indicating randomness.
Experiment 3--Hickok and Davenport (1957) reported com¬
mensals with Patiria selectively responding (PK.001) to
Pisaster giganteus (Stimpson) in a choice apparatus. To
determine whether Ophiodromus commensal with Patiria would
accept alternate hosts in the laboratory, 24 commensals
were equally divided among two P. gigantea and two
Ophiodromus behavior
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M. Serences
Dermasterias imbricata (Grube). Each seastar species was
maintained in a seperate aquaria and examined daily for
Ophiodromus.
Following day 1 only one commensal remained on each
of the Pisaster and by day 2 no commensals were evident
eitheronthe seastars or in the tank itself. No commensals
were observed on the Dermasterias after the fifth day.
Both observations suggest the commensals had been ingested
by their prospective hosts.
Experiment 4--To observe commensal behavior on an injured
host, two slashes approximately one centimeter long were
made through the aboral surface of a Patiria with eight
Ophiodromus. No commensals were observed abandoning their
host during eighteen hours of periodic observations.
During the first hour, however, the commensals remained
within or close to the ambulacral grooves and later move¬
ment was restricted to the oral surface.
Experiment 5—-To determine if commensals would abandon
their host after prolonged air exposure, a Patiria with
ten Ophiodromus was placed in a plastic container filled
with approximately fifteen millimeters of dry sand and
observed periodically for 69 hours.
Commensals remained on their host for at least 25
hours. After 48 hours, however, seven Ophiodromus had
crawled off the host and after 69 hours only one worm
Ophiodromus behavior
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M. Serences
remained on the seastar. The distances traveled from the
host ranged from between .5 to 11 cm (mean of 4.1 cm).
Experiment 6—-To observe what would happen when a large
number of Ophiodromus were forced upon a Patiria, 25
Ophiodromus, of average size 9 mm, were placed on two
Patiria of sizes 5.5 and 6.3 cm, respectively. The 5.5
cm Patiria (A) was not fed throughout the experiment while
an unlimited supply of squid was fed the 6.5 cm host (B).
No more than eighteen commensals would remain on a
given seastar for longer than an hour despite repeated
replacements and, of those, at least four were found
aborally. After 24 hours eleven and six of the initial
worms remained on the seastars A and B,respectively.
Forty-eight hours later three were present on A and one
commensal remained on B.
Experiment 7—-To determine whether Ophiodromus are commensal
with Patiria for feeding purposes, a small piece of mussel
was placed in a crystallization dish filled with sea water
and a Patiria with sixteen commensals, which had been
starved for three days, was placed on top of the food. The
worms'reaction was observed using mirrors positioned so the
oral surface of the host could be seen through a dissecting
microscope.
During the course of an hour four of the commensals
came down to the food and everted their proboscises as many
Ophiodromus behavi
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M. Serences
as four times. The commensals would venture underneath
and above the everted stomach of the seastar, but rarely
went between the folds of the stomach or close to the
mouth.
Experiment 8—-To determine whether the commensals were in¬
deed eating the food of the seastar, fifteen feeding
experiments were conducted. In each case, 25 ml of un¬
filtered salt water, unless specified, was used to prepare
17gms of unflavored gelatin. This was poured approximately
1/2 cm thick into petri dishes and additional substances
were added as noted. Methylene blue was used to dye the
first gelatin and carmine red was used in subsequent ex¬
periments. Patiria with Ophiodromus were starved for
periods noted in Table 3. For each experiment, several
small pieces of gelatin were placed in a crystallization
dish of appropriate size filled with sea water. A seastar
with six commensals was placed over the food. Once the
Patiria had hold of the gelatin, it was placed in a plastic
tank with circulating sea water. Commensals were examined
under a dissecting scope after six, nine and 24 hours
following feeding for any signs of dyed particles within
the gut.
Results and observations are listed in Table 3. The
slashes indicate results from duplicate runs of the same
experiment. Commensal feeding while the host was ingesting
food was observed in six out of sixteen experiments.
Ophiodromus behavior
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Experiment 9—-To quantify the startle response, a sudden
contraction of commensals, the observation container was
given a sudden shake and the reaction of the Ophiodromus
when on top of, near the edge of, or not touching the host
food was noted. Results are summarized in Table 4. A
significantly fewer number of contractions occurred when
the commensal was not touching the food than in either
other case (PA.005, 2x2 Contingency Test).
Experiment 10—-To determine whether diurnal patterns of
commensal movement were obvious, freehand sketches to
scale of commensals positions on a Patiria were made on
graph paper and average distances from the nearest am-
bulacral grooves determined from this. The results are a
compilation of observations made irregularly over a nine
day period and are graphed in Figure 5 as the average
distance of commensals to the nearest ambulacral groove
of the host as a function of the time of day. No periodicity
in movement is apparent.
Experiment 11--To see if free-living Ophiodromus could
adapt to a commensal existence on P. miniata, three frée¬
living conspecifics, obtained among tunicates from wharf
pilings, were placed on a Patiria and observed for five
days. After this period, the seastar was fed a mixture of
unflavored gelatin, carmine red and squid extract.
Following initial placement on the Patiria, free-living
Ophiodromus behavior
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M. Serences
Ophiodromus remained on the seastar throughout the five
day period. Movement was predominately on the oral surface
although worms were occasionally observed aborally. Although
two eversions of the proboscis were noted during host
feeding, no red particles were detected in the guts after
24 hours.
DISCUSSION
Experimental and field results suggest that commensal
distributions on Patiria are at least partially regulated
through behavioral controls. Field distributions showing
a higher occurrence of seastars lacking commensals than
expected from a Poisson distribution could be an indication
of preferential host colonization. When Ophiodromus were
given a choice between two Patiria in the laboratory, host
selectivity was again indicated although a larger sample
size would be required to support this hypothesis. A
random distribution was obtained in the laboratory after
extremely clumped initial conditions yet a longer dispersal
time may be required to obtain experimental distributions
approximating those in the field. Unnatural surroundings
or restrictions of space and food in the laboratory may
also account for this discrepency. Although commensal
densities per seastar increased with increasing host size
in the field, hosts artificially crowded in the laboratory
were unable to maintain large worm densities. Inter- or
intraspecific behavioral interactions may be important in
Ophiodromus behavior
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M. Serences
controlling commensal densities on hosts.
Size differences between commensals from the two
subtidal sampling sites may indicate that growth rates
for Ophiodromus are greater in nearshore and intertidal
habitats than in subtidal regions. Additional ecological
studies are needed, however, to determine the cause of
these findings.
Host abandonment was not observed in the laboratory
except under extreme conditions such as prolonged exposure
to air or overcrowding. Commensal intolerance of such
conditions, rather than host survival, may determine
whether Ophiodromus remains associated with the host.
Ophiodromus may not associate with P. gigantea and D. imbricata
due to host ingestion of the commensals.
Evidence from feeding experiments suggest 0. pugettensis
is commensal with P. miniata for feeding purposes as well
as protection. Commensal movement on the host showed no
periodicity and was generally restricted to the oral surface
of the seastar where protection and food supply seem greatest.
Yet, commensals seemed more selective in food preferences
than host Patiria. This may be of adaptive significance,
however, considering Patiria are scavengers and also of a
cannibalistic nature. It also implies that something
other than stomach eversion may be necessary before a
feeding response is elicited in the commensals.
Neither benefit or harm to P. miniata by its commensal
was indicated. And, initial observations with free-living
Ophiodromus behavior
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M. Serences
Ophiodromus indicate that at least temporary existence on
Patiria can be tolerated. Further studies are needed to
conclude whether such results can be maintained over long
periods of time. Larval settling studies, as begun by
Davenport and Hickok (1957), are also necessary to
elucidate the evolution and nature of these commensal
associations.
Ophiodromus behavior
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SERVATIONAL NOTE
Morphological studies on the polychaete are extremely
limited. Observational notes made in the laboratory are
included here in hopes of aiding further research in this
area.
Seemingly well adapted to its commensal existence,
the polychaete can wedge itself between the oral plates
of the seastar or within the ambulacral grooves to the
point of concealment. Although frequently oriented along
the edge of the ambulacral grooves, movement among the tube
feet is also common and increases when the seastar moves.
Often the worm can be seen extending its body into the water
before crawling from surface to surface of the host, and
will move among the granular tufts when aboral. No aggressive
behavior between commensals and host or between worms was
observed, although the polychaetes rarely lie close to one
another. If inverted, eversions of the proboscis can occur,
apparently in an attempt to right the worm. Commensals re-
moved from their host were not observed to eat small pieces
of squid after a two hour period.
Contained within the posterior segments of the poly-
chaete, is a white substance of unknown constitution and
function. Examination of 66 commensals showed 48 (72.7%)
with white coloration in posterior segments and 18 (27.3%)
without. Of those commensals reported without the white
coloration, eight had emitted the substance after pro¬
vocation while in a dish of slightly warm stagnant sea
Ophiodromus
behavior
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M. Serences
water. The material was not always totally discharged,
however, and anything remaining was concentrated in the
anterior portion of the segments. If the worm is anteriorly
provocated with a sharp instrument it will contract slightly
and back up tail first rather than turning around on itself.
Commensals without or with what appeared to be re-
generated tail segments were also observed. Movement on
and off the seastar did not seem to be hindered by such
alterations. Tail cirri were dyed in methylene blue to see
if any functional adaptations could be detected. Although
generally appearing to drag passively behind the polychaete,
they were frequently observed rigidly extended. Curved
positions, inwardly and outwardly, around tube feet or the
bases or oral plates were also noted. When a swimming
commensal was observed the tail cirri appeared to move in
a whip-like fashion.
Ophiodromus b
age 16
M. Serences
SUMMARY
1. The host-directed behavior of Ophiodromus pugettensis,
a commensal polychaete, was investigated in the field
and laboratory on Patiria miniata over a six week
period during April and May 1976 at Hopkins Marine
Station, Pacific Grove, California.
Field studies indicate:
2.
A. An increase in commensal populations with
increasing host size.
B. Commensal populations of 0. pugettensis
fluctuate with time.
C. Clumped distribution of 0. pugettensis on
P. miniata.
D. An increase in size and growth rate of
O. pugettensis moving intertidally.
3. Laboratory results suggest:
A. Commensal distribution on P. miniata after
small time periods is random.
B. Feeding as well as protection may be the
nature of the commensal existence of 0. pugettensis
on P. miniata.
C. Large number of commensals on individual P. miniata
are uncommon for long periods of time.
D. O. pugettensis populations on P. gigantea and
D. imbricata may be uncommon in the field due to
host ingestion of the polychaete.
E. Commensal O. pugettensis abandonment of P. miniata
is uncommon unless conditions are extreme.
Ophiodromus behavior
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M. Serences
ACKNOWLEDGMENTS
I would like to express my thanks to Chris Harrold,
for helping me with my field studies, Larry Harding and
the Hopkins Marine Station faculty and staff. My deepest
thanks, however, go to Dr. Robin Burnett whose diving
ability, patience, willing advice and profound enthusiasm
made working on this project one of the most memorable
experiences I have ever had.
Ophiodromus behavior
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M. Serences
LITERATURE CITED
Bartel, A. H. and D. Davenport
1956. A technique for the investigation of chemical responses
in aquatic animals. J. Anim. Behav. 4:117-119.
Davenport, D.
1950. Studies in the physiology of commensalism. I. The polynoid
genus Arctonoe. Bid. Bull. 98:81-93.
TT
1953. Studies in physiology of commensalism. III. The polynoid
genera Acholoe, Gattyana and Lepidasthenia Studies in physiology
of commensalism. I
The polynoid generaP.
noe, Lepidasthenia
and Harmothoe. J. Mar. Bio. Assoc. U. K. 32:272-288.
Davenport, D., G. Camougis, and J. F. Hickok
1960. Analysis of behavior of commensals in host-factor. I. A
hesionid polychaete and pinnotherid crab. Anim. Behav. 8:209-218.
Davenport, D. and J. F. Hickok
1951. Studies in physiology of commensalism. II" The polynoid
genera Arctonoe and Halosydna. Biol. Bull. 00:71-83.
257. Notes on the early stages of the facultative commensal
Podarke pugettensis Johnson (Polychaeta: Hesionidae). Ann. Mag.
Nat. Hist., London, Ser. 12., 10:625-631.
Hickok,
J. R. and D. Davenport
1957.
Further studies on the behavior of commensal polychaetes.
3:397-406.
Biol. Bull. 11
Lande, R. and D. J. Reish
1968. Seasonal occurrence of the commensal polychaetous annelid
Ophiodromus pugettensis on the starfish Patiria miniata. Bull.
So. Calif. Academy Sciences
67:104-111.
Reish, D. J.
1961. The use of sediment bottle collector for monitoring polluted
marine waters. Calif. Fish and Game 47:261-272.
C
Ophiodromus behavior
M. Serence
Figure 1 —-Plot of average size P. miniata
versus number of 0. pugettensis per host.
This indicates an increase in the number
of commensals per host with increasing
host size.  indicates two data points.
Page 19
2

4

0
Ophiodromus behavior
M. Serences
FIGURE 1
0
0
o
oo 0
a
ooo0

234 50 789011231
AVERAGE SIZE
P. MINIATA (CM)
Page 20
Ophiodromus behavior
M. Serences
Figure 2--Histogram of number of commensals
per host. Clumping is indicated. Darkened
bars indicate Poisson distributions; slashed
bars observed distributions.
Page 21
Ophiodromus behavior
M. Serences
FISURE 2
LAA
NUMBER COMMENSALS /SEASTAR
Page 22
Ophiodromus behavior
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M. Serences
Figure 3--Graph of number of commensals per
host over time period of 48 hours. represents
host initially lacking commensals. e represents
host with ten commensals initially. Two worms
were without hosts at the conclusion of the
experiment.
S
0
Ophiodromus behavior.
1. Serences
141
12
91
81

4
4
6 12
FIGURE 3
18 24 30 36 42
TIME (HRS.)
48
Page 24
phiodromus behavior
M. Serences
Figure 4--Graph of the number of commensals
per P. miniata versus frequency of occurrence
in the laboratory. A random distribution is
indicated.
Page 25
8
Ophiodromus behavior
M. Serences
FIGURE 4
4
A
14
1

O
3 4
2
5
6
NUMBER COMMENSALS /SEASTAR
Page 26
hiodromus behavior
M. Serences
Figure 5--Graph of time of day versus
average distance of commensals from
ambulacral grooves of the host (cm).
Averages were taken from a number of
commensals on various hosts and com¬
piled over a nine day period. No
obvious patterns were detected.
Page 27
Ophiodromus behavior
M. Serences
1O

I9


L


E
L
O
1

4
FIGURE 5
Page 28
——
8
TIME
O
12
DA
8
12
phiodrom
Serences

Table
1--Records number of commensals o
seastars for dive dates: Indicates
fluctuations in commensal populations
per host.
Ophiodromus behavior
M. Serences
TABLE
1
PATIRIA TAG
NUMBER
NUMBER
2220
4
O
4
3
2
14
O
4
16
18
2
2.
26
3
27
3
20
3.
3
3
38
49
40
Page 30
OF
COMMENSALS
4721
577
52
4
5
5
4
6
10
2
2
2
3
3
O
2
3
2
4
6
6
4
Ophiodromus behavior
M. Serences
Table 2--Area and date of collection,
size range (mm) of 0. puget
collected, sample size, mean, standard
deviation and level of significance.
Area 1 was at a greater depth and dis-
tance from shore. Significant mean
size differences in commensals between
areas is indicated.
Area, dates of comparison and level
of significance between similar pop-
ulations sampled. Indicates a sig-
ficant change in size of commensals.
Page 31
Ophiodromus behavior
M. Serences
TABLE
2
51ZE
AREADATE
N
)(
RANGE
39
75530/1892
12
5/
3-15
111 78472488
2
3-13
38
6.1322244
20
2508
5-
41
9244

2
AREA
VS.
20
2
VS.
26
P VALUE
O0
01
(O3
(002
Page 32
Ophiodromus behavior
M. Serences
lable 3--Number of commensals with
dye in gut af
er time periods of 6
9 and 12 hours after exposure to gel
atin mixture, with indicated addition
and after starvation of indicated
tervals. Slashes indicate resu
from duplicate runs of the same
periment. Six worms were
used
each tria
e
Ophiodromus
M.Serences
MIXTURE
LMETHVLENE
BLUE
CARMINE
+RED
SQU1D
LJUICE
LGIGARTINA
CORYMBIFERA
+EGREGIA
CARMINE
f RED
FPHYLLOSPADIX
GIGARTINA
CORYMBIFERA
+ EGREGIA
CARMINE
RED
SEASTAR
+ JUICE
LPHYLLOSPADIX
SEASTAR JUKE
FPHYLLOSPADIX
CARMINE
RED
SMITHORA
+ NAIADUM
behavior
TABLE
STARVATION
PERIOD
3 DAYS
O DAYS
O DAYS
D DAYS
6 DAYS
7 DAYS
8 DAYS
6 DAYS
3
NUMBER MITH DYE
Oh
Ohr
124
OO

O/
/0
10
1
24
4
0
O
4
4
O
O
O
4
3
6
O
O
2
2
O
O
O
O
10
16
1
O
O
O
O
O
Page 34
OBSERVATIONS
NO EVERSIONS
EVERSIONS
EVERSIONS
SEASTAR DID NOT
INJEST FOOD
NO PROBOSCIS
EVERSIONS
PRIOR TO
STOMACH EVERSIONS
STARTLED' NEAR
FOOD
NO PROBOSCIS
EVERSIONS
PRIOR
0
STOMACH EVERSIONS
PROBOSCIS
EVERSIONS
STARTLED NEAR
FOOD
STARTLED' NEAR
FOOD
SEASTAR DID
NOT INJE
FOOD
SEASTAR DID
NOT INJEST
Foop
todrones behavio
--Reco
ple
sult
onse
Jumb
rimen
tin
the contraction response was obsery
rnumber of trials is lis
ted while
commensal was touch
not touchir
near the host foo
Indication
hat commensals:
re more al
hen
edin
age






4.
1
L
1
Ophiodromus behavior
M. Serences
TABLE
NUMBER TIMES RESPONSE
PER NUMBER TRIALS
CONTRACTION WHILE

TOUCHING TOP
OF FOOD
2
CONTRACTION WHILE
TOUCHING EDGE
2
OF FOOD
CONTRACTION WHILE
NOT TOUCHING
12
FOOD
Page 36