Peters and Rothman
Introduction
The pea crab Pinnotheres pugettensis (Holmes, 1900)
is known from Departure Bay, B.C. and Puget Sound,
Washington, where it occurs in the ascidians Halocynthia
aurantium, H. hilgendorfi igaboja and Ascidia paratropa,
and from Monterey Bay, California where it was recently
discovered in the ascidian Styela montereyensis (Dall,
872) by C. C. Lambert (Garth and Abbott, 1980). The
range of P. pugettensis may extend even further south;
a pea crab was found in one S. montereyensis collected
at Pt. Loma, California (Fay and Johnson, 1971).
Pinnotheres taylori
Pinnaxa faba, and Fabia subquadrata, however
have also been reported from Pacific ascidian hosts
(Schmitt, et al, 1973).
Pinnotheres pugettensis has not been extensively studied.
Very little is known of its occurrence, it position in
and relation to the host ascidian, its methods of feeding,
and its developement. The present research was undertaken
to try and answer some questions in these areas, using
the P. pugettensis population in S. montereyensis
from southern Monterey Bay.
The ascidians studied often harbored the notodelphyid
(Iiig)
copepod Pygodelphys aquilonaris, known on this coast from
studies in Washington, (e.g. Illg, 1958; Dudley, 1966).
Some notes on its occurrence in S. montereyensis in
Monterey are included.
Peters and Rothman
Materials and Methods
Specimens of S. montereyensis were collected between
April and June 1980. Subtidal collections were made from
depths of 15 to 35 feet in kelp beds at Mussel Pt.,
and
Pacific Grove;,Pt. Alones and Wharf no. 2, Monterey,
sing SCUBA. Intertidal collections were made by hand
at Pescadero Pt., Monterey Peninsula, as well as at
Mussel Pt. and Wharf no. 2. Specimens were kept alive
in tanks at Hopkins Marine Station, where they were
suspended from styrofoam floats by plastic clips clasping
the base of the stalk. Aquaria were supplied with
running seawater at 10-15°0, a temperature generally
within three degrees of ambient local ocean temperatures.
Tunicate body volumes were measured by immersing the
body (but not the stalk) of the contracted specimen
in a 100 ml graduated cylinder of seawater and noting
displacement.
S. montereyensis shows no external evidence of
presence or absence of a pea crab. After initial trials,
all tunicates were dissected by making a longitudinal
slit through the tunic from the base of the oral
siphon at the anterior end down to the beginning
of the stalk. The tunic was pulled aside to reveal
the translucent mantle, within which a crab if present,
could usually be observed. The mantle and the pharynx
were then opened with a cut similar to the first incision,
Peters and Rothman
this one running along the length of the endostyle. By
dissecting the tunicate in this manner the crab, in the
atrial cavity, is minimally disturbed; when incisions were
made down either side of the body laterally or on the
dorsal side, the crab usually became active and broke
through the pharyngeal wall into the pharyngeal cavity
of the tunicate. Perhaps this type of action accounts
for at least some of the reported instances of pea
crabs being found in the pharyngeal basket of ascidians
(e.g. Fay and Johnson, 1971).
Crabs found in dissections were removed from the
tunicate, measure with an ocular micrometer, and kept
in running seawater in individual compartments of ice
cube trays fitted with screened plexiglass tops. They
were fed Artemia naupli intermittently, we are uncertain
whether or not they were eaten.
In tunicate and crab feeding experiments, phytoplankton
suspensions (Chaetoceros gracilis and Isochrysis galbana),
colored black with "Aquadag" colloidal graphite or
red with powdered carmine, were used. Tunicates
used in feeding experiments were placed in 10% formalin
and seawater overnight and then dissected.
Various methods of anesthesia were tried in the
course of the dissections. The most successful procedure
was to "tranquilize" the tunicates first in a solution
of menthol in seawater for several minutes then place
Peters and Rothman
them in MS 222 (Ethyl m-aminobensoate, methanesulphonic
acid salt 98%, Aldrich) diluted 1:2000 for five to ten
minutes. This method, however, never completely relaxed
the tunicates. Neither menthol nor MS 222 seemed to have
any effect upon the crab.
Distribution
In the course of the study, 222 subtidal and 25
intertidal Styela montereyensis were collected. In
the subtidal tunicates, 73 Pinnotheres pugettensis were found;
49 were females, and 24 were identified as males.
However, sex identification of the smallest individuals
was difficult. Eight male P. pugettensis were found
outside of S. montereyensis in collecting bags and
in which S
vela were kept.
aquaria The overall infection rate of the subtidal
Styela population was 32.9%. No crabs were found in
intertidal S. montereyensis.
In order to obtain an accurate and useful measure
of tunicate size the authors compared body volume and
body length. Measurements of the stalk were omitted
because its length was highly variable and did not
correlate well with body size. When body length is
plotted against body volume it becomes apparent that
the variance in body volume is less then that for
body length, (see Fig. 1). Consequently body volume was
used as a measure of tunicate size.
Peters and Rothman
No statistically significant difference in body
volume was found between intertidal and subtidal
populations of Styela (Student's t-test, p-.02). An
Rx C contingency test showed the difference in P.
pugettensis infection rates between subtidal and
intertidal Styela populations to be highly significant
(p£.01). Some caution, however, must be exercisized
when interpreting these results; 19 of the intertidal
Styela were collected at Wharf no. 2, but none of the
six subtidal tunicates found at the Wharf contained
P. pugettensis. The difference in infection rates may
be due to some other factor than differences in tidal height.
Of the infected tunicates 62 contained one crab,
four held two crabs, and one tunicate contained three
much
adult
crabs. Male crabs were generally,smaller thangfemales.
Males had an average carapace width of 4.Omm (SDt1.6imm).
The smallest male had a carapace width of 1.Omm and
carapace length of 0.9mm; the largest male was 6.8mmx 6.Omm.
Female crabs had an average carapace width of 8.2mm
(SDt1.5mm). The smallest female had a carapace 5.2mm x 5.2mm,
while the largest was limmx iimm.
There was a moderate positive correlation (r = 0.35)
between crab carapace width and body volume of the
tunicate (see Fig. 2). This positive relationship
between host size and crab size has been found in other
Pinnotheridae (Pearce, 1966a; Christensen and MeDermott,
Peters and Rothman
1958 ; and Silas and Alagarswami, 1967). This
correlation is better (r = 0.56) if the few cases
of multiple infections are omitted. The rate of
infection varied with tunicate body volume; additionally,
as volume increased, fewer males and more females
were found (see fig. 3).
The infection rate of subtidal S. montereyensis
by the copepod Pygodelphys aquilonaris was 30.2%.
No copepods were found in Styela taken intertidally.
An Rx C contingency test showed the difference between
the intertidal and the subtidal infection rates to be
highly significant (p«.01). However, subtidal Styela
at Wharf no. 2 lacked copepods, just as they lacked
pinnotherid crabs. The infection rate with P.
aquilonaris varied with the size of the tunicate (see
fig. 3). Multiple infections were fairly common; the
largest number of copepods within a single host tunicate
was 15 (see fig. 4). Copepods were found only within the
ascidian pharynx.
Position and feeding of crab in host
Of the total of 73 Pinnotheres pugettensis found
in Styela montereyensis, one crab was found within
the branchial basket, while 72 were located in the
anterior third of the atrial cavity. The ventral
surface of the crab was always in contact with the
pharynx, the dorsal surface towards the tunic. The
Peters and Rothman
crabs legs were held closely against the body; not
grasping the tissues of the ascidian. Connective tissue
ascidian
strands and blood vessels joining the mantle to the
pharynx were interrupted by the presence of the
crab, but these same tissues in the area surrounding
the crab remained intact, thus the crab was maintained
in position in a sort of pocket. P. pugettensis was
found in either the left or right side of the atrial
cavity, but always with the mouthparts and chelae
within 3mm or less of the dorsal lamina, and facing it.
A crab on the right was positioned as in fig. 5a, a
crab on the left was rotated 180 degrees. Crabs
positioned dorsally in the atrium were oriented with the
mouth in the closest proximity to the dorsal lamina of Styela
(see fig. 5b).
A consistent feature of S. montereyensis containing
P. pugettensis in the atrium was a hole in that part of
the pharyngeal wall located close to the mouth of
the crab (see fig. 6 and 7). This hole was 1-3.5mm
in diameter, its size positively correlated with the
size of the crab. The hole appeared well healed, the
edges were smooth, and the blood vessels of the pharynx
were fused and diverted around the hole. Slight damage
was occasionally observed to the dorsal lamina in the
region next to the hole. (Additionally, when the
crab infecting a tunicate was large the testes of the
Peters and Rothman
ascidian behind the pocket containing the crab were
reduced in both size and number). Where more than
one crab was present in the tunicate, each crab had
its own hole; one crab occurred in the usual position
while the additional crab was located either at the same
level in the atrium on the opposite side of the pharynx,
or lower down in the atrium on the same side as the first
crab.
The position of the crab in the host, and the
neat hole in the pharyngeal wall of the tunicate,
strongly suggested thatt the crab was feeding on the
mucus rope formed at the ascidian dorsal lamina.
S. montereyensis is a suspension feeder, like all
ascidians, and collects food particles by passing surrounding
water through mucus nets. These nets, which line the
pharyngeal cavity, are secreted by the endostyle, then
passed across the gill slits on both sides of the pharynx
until they reach the dorsal lamina where the sheets from
each side are rolled together into a rope and passed down
to the ascidian esophagus (see Jørgensen, 1966; Fiala¬
Médioni, 1978; Flood and Fiala-Médioni, 1979). To test
whether the crab might be feeding on this mucus rope,
phytoplankton marked with "Aquadag" colloidal graphite
or powdered carmine was pipetted into the region of the
oral siphons of submerged, feeding tunicates. Each of
25 subtidally obtained Styelas was fed for 10-15
minutes. For an additional 15-45 minutes each ascidian
was submerged in seawater containing a less concentrated
10
Peters and Rothman
mixture of the marker and plankton, finally the animal
was killed in a 10% formalin 90% seawater solution.
Subsequently the tunicates were dissected and the
pharynxes opened. The mucus rope was usually well
stained, appearing bright red or black dependent upon
the marker used. Nine P. pugettensis were found
within these ascidians, and all were carefully removed.
Six crabs had the mouthparts and chelipeds stained
with the colored mucus, and one was found clutching the
mucus rope. Of the above six crabs, three contained
dyed food particles in their cardiac stomachs.
P. pugettensis does not leave the host to forage,
or even move about much within the host atrium, as
indicated by the pocket created by the tissue strands
and blood vessels encircling the crab.
The hole in the ascidian pharynx was always small
and almost always well healed, indicating the injury was
not recent, and that the crab was not actively eating the
pharyngeal tissue. Tunicates containing some of the
larger crabs often showed additional scaring of the
pharyngeal wall directly next to the body of the crab,
but never another hole. S. montereyensis, in the lab,
were able to completely heal holes cut in the pharyngeal
wall within 1-2 weeks. Further, the crab was always
11
Peters and Rothman
located posterior to the anal pore of the ascidian, and
was in the wrong position to capture and feed on
ascidian fecal pellets. Moreover, in the feeding
experiments with stained food the crabs were eating
colored material, yet upon dissection of the tunicate
gut it was found that the dyed mucus had passed no
further than the stomach. These observations all
indicate that P. pugettensis is reaching into the
pharynx with its chelipeds or mouth parts, through a
single small and strategically placed hole in the
pharyngeal wall, and feeding upon the mucus rope as it
passes down the dorsal lamina.
No evidence was found to support previous statements
that P. pugettensis is a filter feeder (Wells, 1940,
Peters and Rothman
Christensen and MoDermott, 1958; Silas and Alararswami,
1967). An examination of crab mouthparts shows no
obvious adaptions for filter feeding, and it seems
unlikely that the crab could get sufficient quantities
of particulate food through the network of the pharyngeal
basket, even on occasions when the mucus sheet is not
being secreted. It would seem far more advantagous for
the crab to take advantage of the highly efficient
filtering and collecting mechanisms of the tunicate.
by simply stealing portions of the mucus rope as it is
being passed back to the ascidian esophagus.
The pea crab obtains both food and shelter from
S. montereyensis. The food-robbing process probably
produces only a small loss
to the ascidian
host. Further stress may be placed on the host by
disrupted tissue strands and blood vessels, the hole
in the pharynx, slight damage to the dorsal lamina, and
some disruption of the gonads. The reduced testes would
be expected to reduce the tunicates reproductive fitness.
as is proposed by Berner (Silas and Alagarswami, 1967)
Pinnotheres pisun
for
in the mussel Mytilus edulis, and Christensen
and MeDermott (1968) for Pinnotheres ostreum in the oyster
Crassostrea yirginica. However, this may be relatively
insignificant in Styela, since testes are very numerous
and those on the opposite side and below the crab appear
unaffected. Additionally the ovaries appear undisturbed
Peters and Rothman
by the presence of a crab. No evidence was found in
S. montereyensis of severe enlargement of the mantle
or atrial cavity toaccommodate individual crabs as
aurantium from
shown for Halocynthia (-Tethyum)
Puget Sound infested with P. pugettensis(see Wells, 1928).
In our estimation, the damage sustained by S.
montereyensis is relatively minor. No quantitative
measure of food taken was made, but the S. montereyensis
containing crabs were not significantly smaller than
S. montereyensis without crabs. In general the
destruction appeared much less severe then that caused
by the behavior of some other commensal crabs, particularly
those infecting bivalves, Fabia subquadrata, Pinnixa faba,
P. littoralis (see Pearce, 1966, 1966a; Anderson, 1975) and
Pinnotheres ostreum (see Sandoz and Hopkins, 1947;
Christensen and McDermott, 1958)
Larval Stages
Twenty living gravid females were obtained from
tunicate dissections in the course of this study. Eight
of them subsequently hatched larvae. Immature eggs were
maroon in color, changing to orange as they developed,
and then to a light tan 4-5 days prior to hatching. One
ovigerous female (9.0 x 9.0 mm) contained approximately
2700 eggs. Developing eggs overflowed the sides of the
Peters and Rothman
abdominal plate. A brooding female removed from
the tunicate
often brushed away the excess eggs
with her legs and chelae, regardless of the developmental
state of the eggs. The remaining eggs under the abdominal
plate developed and hatched normally.
Expectant females were placed in quart jars in a
seawater bath, following the methods of Irvine and
Coffin (1960) who were successful in raising the larva
of Fabia subquadrata. When larva hatched they were
divided into groups of 30-50 and placed in individual
jars in the seawater bath. Depth of water in the jars and
seawater bath was 15-20cm. Temperature of the bath was
10-15°0 during the course of experiment


Larva were fed Artemia nauplii and had their water
changed daily. All larval measurements were made
using an ocular micrometer.
Developement
The eggs of P. pugettensis hatched directly to
an advanced zoea stage. There was no free protozoea.
Amolt occurred after 10-12 days to a second zoea
stage. At 21-24 days this second zoea moltéd to a
megalops stage. At 28-30 days this megalops molted
to the first juvenile crab instar.
14
Peters and Rothman
First Zoea (see fig. 8)
Carapace 0.58 x 0.58 x 0.42mm; duration of stage 10-12
days. Characterized by a pronounced rostrum O.2imm
long, and a curved dorsal spine 0.18mm long. Eyes
sessile, 0.15 x 0.2 mm. First and second antennae
0.lomm long. Four setae on each of the second and third
makillipeds, which are the longest appendages; rear
thoracic appendages uniramous and undifferentiated.
Abdomen six-segmented; telson 0.33 mm long with pronounced
point on either side and six short spikes in center.
Each abdominal segment with a pair of uniramous
periopod buds 0.05-0.08mm in length. Zoea positively
phototactic, found swimming at top of rearing containers.
Second Zoea (see fig. 9)
Carapace 0.6 x 0.6 x O.5mm; duration of stage 10-12 days.
Differentiated from first stage by larger carapace,
longer straight rostrum (0.Emm), and curved dorsal
spine 0.3mm long. Eyes
stalked and mobile, compound
eye 0.19 x O.19mm, stalk O.5mm. Small ventral spike
below the eyes O.15mm long. First antennae 0.15mm long
with terminal setae O.05mm. Second and third maxillipeds
still the longest appendages, but now each bears six
terminal setae 0.35mm long. Rear thoracic appendages
still undifferentiated. Abdomen six-segmented with
uniramous periopods now O.imm long. Telson O.Amm long.
still forking to two points each 0.15mm long; six
15
Peters and Rothman
16
central, thickened setae 0.07mm long present between
the points. Zoea still positively phototactic; normally
remains at bottom of jar but swims upward toward a
strong light source held above the container.
Megalops (see fig. 10)
Carapace 0.58 x 0.58; duration 6-7 days. Eye stalks
elongated and thickened, o.25mm long, compound eye
0.13 x 0.13mm. Antennule biramous, O.25mm long;
antenna 0.25mm with two terminal setae O.25mm long.
Chelipeds 0.34mm long with both digits of claws hooked
and overlapping at tip; both chelipeds bent slightly
inward at center. Last four thoracic appendages well
developed. Abdomen six-segmented with telson small
and rounded posteriorly. Pleopods, now used for swimming,
0.15mm long, each with 3 terminal setae O.35mm long.
Megalops swam actively or settled and walked; when
placed in bowls of sea water with S. montereyensis,
they ignored the tunicates.
Peters and Rothman
Adults (see fig. 11)
The only previously described P. pugettensis
adult is the female (Holmes, 1900; Rathbun, 1918;
Wells, 1928; and Schmitt et al, 1973). Males found
during the present study differ from females in
Adult
numerous respects. females are characteristically
adult
translucent and soft shelled, males are brown and
hard shelled. Females have rounded smooth chelae and
legs with short trailing hairs, males have flattened
legs with longer trailing hairs and their chelae
are angular and sculptured to fit the contours of the
front of the carapace. Female chelae are not sculptured
to fit the front of the carapace. Males are characteristically
smaller than females. There are at least five molts
female and three in the
male (see
in the
fig. 12). Specimens have been deposited in the Allan
Hancock Foundation, University of Southern California,
and the California Academy of Sciences, San Francisco.
Eight males were found outside of tunicates, in
our collecting bags and,aquaria where specimens of
tyela were kept. No free-living males were found
except these which were on or with specimens of Styela.
Only one female was found outside a tunicate and that
was in a stagnant bowl inadvertently left for several
days -- all tunicates in the bowl were dead; four males
and a female crab were found outside of the tunicates
17
Peters and Rothman
18
in the bowl.
Several female crabs removed from tunicates were placed
in screened boxes with S. montereyensis. They attempted
to re-enter the tunicates. In one test, seven out of
eight females chose the oral siphon and one chose the
atrial siphon. In another experiment two females suceessfully
entered a tunicate already containing another female; both
intruders entered the oral siphon and were found one day later in
the pharynx. When females were placed in a box with the
ascidian Ciona intestinalis they ignored the tunicate,
but climbed on a Styela montereyensis when offered.
Only two males from nine trials successfully reentered
a tunicate; they entered the atrial siphon. Of the
cases of double and triple infestations, males were
found with males, males with females, but no females
with females were found.
Discussion
Pinnotheres pugettensis passes through two zoeal
stages and a megalops stage. It is not known at which
stage the crab invades the host. Phototactic response
decreases at each successive larval stage, suggesting
that, though possibly dispersed during the first zoeal
stage, the larvae tend to settle towards the bottom and
therefore toward their potential host. The relatively
advanced first zoea and the short larval cycle of 28-30
days also suggest that P. pugettensis larvae
19
Peters and Rothman
tend to remain in the micro-habitat of their host. No
megalopae were ever seen inside a tunicate. This does
not exclude the possibility that a megalops may enter
and then molt into a juvenile crab, but megalopae and
the one first stage juvenile instar collected did not appear
attracted to Styela when placed in close proximity with
the host.
Only one crab, tentatively identified as a male, was
found in the pharyngeal cavity of a Styela. On close
examination there appeared to be no hole through the pharyngeal
(carapace 0.9 x 1.0
wall into the atrial cavity. This crab was larger,than
the first stage juvenile instar (carapace 0.58 x 0.69mm).
but was the smallest crab found in a tunicate and the
only one not found in the atrial cavity. It was also
smaller than the smallest crab feeding hole found in the
pharynx of any Styela (1.0 x 1.0 mm). Perhaps one
of the juvenile instars is the first invasive stage,
entering the tunicate first through the oral siphon and
then breaking through the pharyngeal wall into the atrial
cavity where it takes up residence. This might also
explain the formation of a pocket by the invading crab,
and the tendency of adult females removed from the host to
reenter through the oral rather than the atrial siphon.
Very small males (2.8 x 2.8 mm) were found in Styela
with feeding holes, while most males found outside the
tunicates were relatively large (4.0 x 4.Omm to 6.4x 6.4mm).
There is one report of a male found free by F. A. Pitelka
on the holdfasts of the sea grass Phyllospadix (cited in Schmitt,
et al, 1973); Rathbun (1918) also reports two
Peters and Rothman
females that were collected free-living. No free-living
females were collected or observed by the authors.
The sizes of the adult females, their gross morphology,
and their locomotory limitations make it hard to envision
them free-living. Silas and Alagarswami, 1967, in a review
of the literature find no evidence for free-living
adult female Pinnotheres. The male being smaller and
more motile might perhaps leave the host to breed,
explaining the large number of males found outside of
tunicates, though no breeding behavior was observed.
Summary
The commensal pea crab Pinnotheres pugettensis
inhabits about 33% of the subtidal population of its
ascidian host, Styela montereyensis, in southern Monterey
Bay, California. No pea crabs were found in intertidal
S. montereyensis. Of 247 tunicates dissected 62 contained
one crab, four held two crabs and one tunicate contained
three crabs. There was never more than one adult female
P. pugettensis per tunicate. The crabs Iive in the
in the anterior third of the atrial cavity of the tunicate,
and feed by reaching into the pharyngeal cavity, through
a small well-healed hole situated dorsally in the pharyngeal
wall, and taking pieces of the rope of mucus and trapped
food particles rolled up by the ascidian dorsal lamina,
We saw no evidence of filter feeding by adult P.
pugettensis. Eggs hatch as advanced zoeae, which molt
to a second zoeal stage in 10-12 days, to a megalops at
20-24 days, and to the first juvenile instar at 28-30
20
Peters and Rothman
21
days. Adult males are dark brown and hard shelled, and
generally smaller than the translucent and soft shelled
adult females.
Acknowledgement:
We would like to thank Dr. Donald P. Abbott for
his incredible energy and guidance, Dr. Isabella Abbott.
Dr. Robin Burnett, Dr. Gary Wagenbach, Chuck Baxter and
the spring students and staff of Hopkins Marine Station.
Peters and Rothman
22
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pea crabs of the genus Pinnotheres Latreille.
Mar. Biol. Assoc. India Symp. Ser., 2(3):1161-1227.
Wells, W. W., 1928. Pinnotheridae of Puget Sound,
Puget Sound Biol. Stn. Publ., 6:283-314
—, 1940. Ecological studies on the pinnotherid
crabs of Puget Sound. Univ. Washington Publ.
Oceanogr., 2:19-50.
24
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Peters and Rothman
Figure captions
Fig. 1 Relation of body length to body volume in the
ascidian Styela montereyensis.
Fig. 2 Relation between carapace width of Pinnotheres
pugettensis and body volume of Styela montereyensis
Fig.3 Numbers of crabs (Pinnotheres pugettensis) and
ascidicolous copepods (Pygodelphys aquilonaris) found,
and percent infestation for each size class of Styela
monter eyensis. N is total number of tunicates in
each size class dissected. Numbers on bars indicate
percent infestation.
Fig
4 Numbers of male and female Pygodelphys aquilonaris
found together in pharynges of individual Styela
montereyensis. Number at each dot shows total number
of ascidians containing each ratio. Female copepods
outnumber males.
5 Diagrams of Styela montereyensis dissected by a
Fig
midventral cut through body wall and pharynx along
endostyle and laid open, showing position and orientation
of Pinnotheres pugettensis. Crab in the atrial cavity
is seen through the pharyngeal wall. Hole through
pharyngeal wall is within 3mm of dorsal lamina.
6 Ventral view of Styela montereyensis with pharynx
Fig.
laid open by a cut along the endostyle, showing hole
through pharyngeal wall interrupting a pharyngeal fold
next to the dorsal lamina. The crabs mouthparts are
directly behind the hole.
Peters and Rothman
Fig. 7 a) Closeup of hole through pharyngeal wall of
tyela montereyensis shown in figure 6 illustrating
smooth edges of the hole. The tips of the crabs
chelae are visible through the mesh of the pharyngeal
wall.
b) Another view of a hole in the pharyngeal wall
of Styela montereyensis.
Fig. 8 Pinnotheres pugettensis, first zoea.
Pinnotheres pugettensis, second zoea.
Fig. 9
Fig. 10 Pinnotheres pugettensis, megalops.
Fig. 11 Pinnotheres pugettensis, male and female adults,
dorsal and ventral views.
Fig. 12 Relation of carapace length in Pinnotheres pugettensis
to carapace width. Vertical lines signify points at which
molting individuals were found, symbols at base of
line indicate sex of molting individuals. Horizontal
line indicates range of carapace width of ovigerous
females.
Peters and Rothman
Hopkins natural history notes:
1) Approximately 350 Styela montereyensis were
collected from the subtidal sites marked on the
following map.
2) Styela were found to have excellent regenerative
abilities, healing damage to the pharynx, mantle and
tunic. Many radical operations were performed with
a low mortality rate, one Styela had its tunic removed
from siphons to stalk, and survived for two weeks,
at which time it was sacrificed.
Taking advantage of the Styelas ability to survive
severe trauma, the authors sewed several windows into
tunicates. A longitudinal incisison was cut through the
tunic, then the mantle, or the mantle and pharynx were
cut, again longitudinally. The window was then sewn
into place using 000 stainless steel sutures. The
window was made of 1/8 inch plexiglass with 1/32" holes
drilled in its perimeter at 1/2" intervals. The window
provided a clear view of the interior ofthe tunicate.
The tunicates operated on survived for at least two weeks.
This method is workable, but has several disadvantages,
it is time consuming, care must be exercised to avoid the
gonads on first incision or they will obsturct the window,
and the amount of force necessary to sew through the
tough tunic may disrupt the tunicate's internal order.
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