L
JOURNAL
SIZE,
OF CRUSTACEAN
BIOLOGY,
17(Z):
217-226,
1997
DISTRIBUTION,
AND SIGNIFICANCE
OF CAPITULAR
OCTOLASMIS
(CIRRIPEbIA:
POECIi;A’SMATIDAE)
Harold
: ?S,..,’
K. Voris and William
PLATES
IN
B. JeJScries
ABSTRACT
All adult Octolasmis live permanently fixed to animate hosts by a basal attachment disc. The peduncle connects the disc to the plated capitulum. The area of the capitular plates and the capitular
perimeter bordered by plates is assessed for 28 species of Octobsmis. A, hypothesis that the species of Octolasmis that live inside decapod gill chambers will have smaller, more variable plates
than those species that live on the exposed external surface of their hosts is articulated and tested.
The data support the hypothesis under general conditions and also reveal an array of special circumstances suggesting that several aspects of host morphology and habits may also impact on the
intensity of selection on capitular plate size and distribution.
Within the superorder Thoracica Darwin,
1854, the order Pedunculata Newman, 1987,
includes the superfamilies Praelepadoidea
Chernyshev, 193 1; Heteralepadoidea NilssonCantell, 1921; Scalpelloidea Pilsbry, 1916;
and Lepadoidea Darwin, 185 1 (see Anderson,
1994). The families of the Lepadoidea (Lepadomorpha) are differentiated on “. . . presence or absence of, degree of development,
and number of capitular plates . . . ” (Zullo,
1982). Within the Lepadoidea, the approximately 60 species of the family Poecilasmatidae are relegated to the genera Octolasmis (28[+]), Trihsmis
(1 [+I), Temnaspis
(9[+]), Megalasmu (14[+]), and Poecilasma
(3[+]) (Zevina, 1982).
Species of Octolusmis are primarily associated with other living creatures such as
corals, echinoderms, mollusks, crabs, lobsters, isopods, horseshoe crabs, fishes, and sea
snakes (Jeffries and Voris, in press). Adult
Octolusmis depend on these hosts as substrata
and perhaps for protection and nutrition. This
paper attempts to explore relationships among
the variations in calcareous plates that occur
on the surface of the capitulum of Octolusmis and their possible functions. Until now
anatomical observations and only anecdotal
references to the relationship of plate variation and function exist in the literature on the
species. For example, it was reported that 0.
indubia Newman, which lives more exposed,
e.g., on the moutbparts of the host, has a capitulum which is more completely plated than
is the case with 0. Zowei (Darwin), which
lives protected in the gill chamber of the host
(Newman, 1961). The speculation has been
that robust capitular plates afford protection
to species like 0. tridens (Aurivillius)
and
0. wurwickii Gray that occur on exposed
parts of the host carapace and appendages,
whereas the host gill chamber affords protection for 0. ungulutu (Aurivillius)
which
has reduced capitular plates (Foster, 1987).
We assert that the calcareous plates have
two primary functions: protection and support. The purpose of this paper is to quantify
the surface area that the capitular plates cover
individually
and collectively in relationship
to the lateral surface area of the capitulum,
to estimate the amount of the peripheral region of the capitulum that is supported by
plates in species of Octolusmis, and to combine these measures with information on the
host associations of each species to test the
hypothesis that plates are reduced, and/or
more variable, among species living in the
protected microhabitats.
This hypothesis evolved as follows: if the
calcareous plates afford species of Octolusmis protection from abrasion and predation
by shielding the capitular tunic and the soft
parts therein, larger plates will provide more
coverage and protection of the capitulum.
Thus, those species of Octolasmis most in
need of protection (e.g.; most exposed to predation and abrasion because of their locations
on their hosts) will have the largest plates.
Some species of Octolasmis may have acquired protection from abrasion and predation
through the selection of host species with attributes such as large size, secretive life style,
or venomous structures that offer special protection, Such species of Octolasmis would be
expected to have less of their capitula covered by plates than would those selecting
217
**
218
JOURNAL
OF CRUSTACEAN
BIOLOGY,
VOL.
17, NO.
2, 1997
of the capitulum should be observed among
those species exposed to less turbulence.
This argument also implies
that the
arrangement of large plates covering most of
the capitulum was acquired very early in the
evolution of the Pedunculata and that the absence or reduction of plates in Octolusmis is
a secondary loss. This is suggested by the fact
that five (2 scuta, 2 terga, and carina) chitinous capitular plates were associated with
some of the earliest members of the suborder Praelepadomorpha
(order Pedunculata),
a group represented in the Carboniferous by
Pruelepas jaworskii Chernyshev (193 1) (see
Schram, 1982). In addition, some evidence
suggests that a pair of chitinous plates may
have been present since the Silurian, when the
genus Cyprilepas (suborder Cyprilepadomorpha) was commonly associated with the exoskeleton of eurypterids (Wills, 1963).
TERGUM
1
MM
Fig. 1. Line drawing of Octolasmis Zowei illustrating the
location and shape of the three capitular plates measured
in this study.
hosts affording little such protection. It would
also be expected that those species of Octolusmis selecting protected sites on their hosts
(e.g., within decapod gill chambers) will have
less of their capitula covered by plates than
those species selecting exposed sites. We predict that in each of the above cases, variability in plate size will be highest in those species that have the least plate coverage. This
prediction follows from the proposition that selection pressure to maintain plates for protection is relatively relaxed among those species
that live in circumstances that afford protection by other means. An additional prediction
is that plate reduction will be at a minimum
among those forms that live on the external
surface of their hosts in the shallow photic
zone where potential visual predators abound.
All species of Octolasmis are suspension
feeders that depend on currents to bring food
to them and the cirral fan to capture it. It is
likely that feeding activity requires some capitular structural support. If the calcareous
plates provide structural support to the capitulum, it follows that species exposed to
stronger currents and turbulence will have
plates that provide greater amounts of support. Conversely, diminished structural support
MATERIALS AND METHODS
The capitulum of poecilasmatid barnacles is typically
characterized by 5 external calcareous plates: the paired
scuta bordering the aperture and the distal end of the peduncle; the paired terga on the more distal border of the
aperture; and the fifth plate, the carina, which forms a
supporting spine adjoining the halves of the capitulum
(Anderson, 1994). Figure 1 shows the location of these
plates on the cosmopolitan species 0. lowei.
Using an ocular micrometer, the capitular lengths and
capitular widths of all specimens were measured and
recorded in mm. The capitulum is often irregular in thickness and surface contour. However, with the aid of a camera lucida, 2 planar drawings were made of each specimen, 1 view from the left side and 1 from the right. Usually, each view depicts 1 scutum, 1 tergum, and the
portion of the carina visible from that view. Octolasmis
collare Jeffries, Voris, and Yang has a collar rather than
2 terga, but the collar measurements were placed under
the terga designation for computational and comparative
purposes. A Keuffel and Esser Number 620005 planimeter was used to measure the areas of the plates and the
capitulum on the drawings in mm*. A Keuffel and Esser
map measurer was used on the drawings to determine
the total perimeter of the capitulum as well as linear segments of the capitular perimeter bordered by plates, and
recorded in mm.
One female mangrove crab, Scylla serrata (Forsk&l)
(carapace width = 96.5 mm), collected at Singapore in
June 1983, provided a large series of Octolasmis angulata and 0. COT(Aurivillius) from the same gill chamber
(Jeffries et al., 1991). The fact that large series of both
species were available on a single crab minimized variability that might otherwise be due to differences among
crabs in terms of size, capture location, etc. The exact
attachment sites of all of the barnacles on the gills of the
crab were noted as each barnacle was removed and pre-
I
VORIS
AND
JEFFRIES:
CAPITULAR
Table 1. The 28 species of Octolasmis included in this
study are listed alphabetically, along with their sample
sizes. The means, standard deviations (SD), and ranges
of capitular lengths are given in mm. Those species in
permanent whole mount slides are indicated by an asterisk. Octolasmis angulata is represented by two samples
and Lepas ansertfera is included for comparative purposes.
Capitular
Number
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
americanum
aneulata
a&lata*
antiguae
aperta
avmonini
brevis
bullata*
californiana
carpilii*
clavula
collare*
0.
0.
Q.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
dawsoni
forresti
geryonophila
grayii
hawaiense
hoeki
indubia
lowei
mtilleri
neptuni
orthogonia
scuticosa
tridens
0. car
0. uncus
0. warwickii
0. weberi
Lepas ansertfera
Mean
1 8.29
19 2.40
13 1.57
2 4.29
11 1.98
10 6.88
4 1.54
4 1.64
4 4.04
9 2.30
4 5.08
22 1.59
20 2.53
5 2.29
11 2.95
61 2.21
10 4.53
9 4.18
3 2.96
5 1.43
10 3.29
10 2.62
10 1.43
2 9.87
11 3.48
10 2.56
2 3.58
10 6.06
4 6.47
14 11.59
length (mm)
SD
oY4
0.39
0.14
0.25
1.12
0.41
0.66
1.36
0.71
0.94
0.21
0.43
0.14
0.63
0.66
0.67
1.87
0.83
0.34
0.29
0.23
0.25
0.20
0.66
0.25
0.43
0.74
1.40
3.82
Minimum
Maximum
1.72
1.15
4.15
1.43
4.86
E
300
2.60
4.43
2.29
8.15
1.90
2.40
5.58
3.15
6.15
1.86
3.28
2.43
4.00
4.15
5.86
6.15
3.43
1.86
4.00
2.86
1.86
10.00
5.01
2.86
4.00
7.15
7.87
19.34
2157
0.86
4.00
1.00
1.57
2.15
2.15
1.00
3.72
1.00
2.00
1.14
2.86
2.15
1.14
9.72
2.29
2.15
3.15
5.00
5.01
5.00
served. Later, each barnacle was measured and drawings
were made of the right and left sides of the capitulum.
Of the total 140 0. car (capitular length range = 1.43-3.00
mm), a subset of 61 was selected for the plate study. Of
the total 88 0. angulata
(capitular length range =
2.14-3.43 mm) a subset of 65 was selected. By this selection of individuals a balanced representation of all the
available size classes was obtained. Area and perimeter
measurements were made from the drawings of each of
the barnacles in these subsets.
Some species used in this study were collected from
decapods and sea snakes obtained in southeast Asia over
a period of years beginning in 1981 (Jeffries et al., 1982,
1984, 1988, 1989). From these collections, 10 specimens
each of 0. grayii (Darwin), 0. neptuni (MacDonald), 0.
tridens, and 0. warwickii
were selected for measurement
and drawing. In addition, 10 0. mtilleri (Coker) which
came from Callinectes sapidus Rathbun from Beaufort,
North Carolina (Jeffries and Voris, 1983); 14 Lepas
anserifera
Linnaeus collected near Phuket, Thailand; and
various museum specimens, including 0. americanum
Pilsbry, 0. antiguae (Stebbing), 0. aperta (Aurivillius),
PLATES
0. aymonini
(Lessona and Tapparone-Canefri), 0. brevis Pearse, 0. californiana
Newman, 0. clavula Hiro, 0.
a’awsoni Causey, 0. forresti
(Stebbing), 0. geryonophila
Pilsbry, 0. hawaiense Pilsbry, 0. hoeki (Stebbing), 0.
indubia, 0. Zowei, 0. orthogonia
(Darwin), 0. scuticosa
Hiro, 0. uncus Peruse, and 0. weberi (Hoek) were also
selected for measurement and drawing (Table 1). All were
preserved whole specimens, of which temporary aqueous mounts were made between a cover glass and slide.
Drawings were made from these mounts, and the area and
perimeter measurements were made on the drawings as
outlined previously.
Three species obtamed in Singapore and Malaysia as
a result of previous work, 0. bullata (Aurivillius), 0.
carpilii Rosell, and 0. collare (see Jeffries et al., 1982),
were available only on permanent microscope slides. To
compare the effects of preparation techniques on the
drawings and measurements made therefrom, permanent
slides of 0. angulata were also prepared.
RESULTS
Intraspecific
I
219
IN OCi-OL4SMIS
Variation in Samples and
Measurements
Bilateral Comparisons.-Comparisons
of the
measurements and the percentage calculations
for the left and right sides of the capitulum
were made in both 0. angulata and 0. col;
both of which were represented by large samples. In 0. angulata, the mean capitular area,
carina area, scutum area, and capitular
perimeter were all larger on the left side than
on the right side. The differences in capitular areas between the left and right sides (left
side = 57.40 mm*, SD = 11.49 versus right
side = 56.60 mm*, SD = 10.76) proved to
be significant (t = 2.62, d.j = 64, P < O.Ol),
as were the differences between the areas of
the scutum on the left and right sides (left side
= 4.43 mm*, SD = 1.04 versus right side
= 3.74 mm*, SD = 0.84; t = 8.75, d.J = 64,
P c 0.001). In 0. col; both the mean capitular area and the mean scutum area were larger
on the left side than on the right side, but only
the differences between scutum areas of the
left and right sides (left side = 7.94 mm*,
SD = 4.13 versus right side = 7.28 mm*, SD
= 3.54) proved to be significant (t = 2.95, d.j
= 60, P < 0.01). The data for these intraspecies left and right side comparisons met
both normality and equality of variances criteria required by the t-test. In no case was
the right side significantly larger than the left
side in either 0. angulata or 0. COT.
In 0. angulata, the mean percentage area
of the capitulum covered by both the carina
and the scutum was larger on the left side
than on the right side. The difference in per-
.,
220
JOURNAL
OF CRUSTACEAN
BIOLOGY,
VOL.
17, NO. 2, 1997
Table 2. For two species of Octohmis the mean, standard deviation (SD), and coefficient of variation (CV) are
given for the percentage of capitulum perimeter supported by plates, and the percentage of area of the capitulum
covered by the carina, the scutum, and the two plates combined.
0. agnulafa
(h’ = 65)
Percentage of capitulum
Meall
SD
Supported
Carina area
Scutum area
Both mates area
54.39
2.15
1.18
10.53
6.66
0.58
1.43
1.76
0. cor(h’=61)
cv
12.24
21.09
18.38
16.71’
centage covered by the scutum was significant (left side = 7.79%, SD = 1.43 versus
’ right side = 6.66%, SD = 1.10; t = 8.14,
Ir_ld.J: = 64, P c O.OOl), as was the same comparison within 0. car (left side = 21.28%,
SD = 6.57 versus right side = 19.76%, SD
= 5.91; t = 3.03, d.$ = 60, P < 0.01).
Although the above documentation
of
asymmetry is new for OctoZasmis, it is not
unique among pedunculate barnacles (Anderson, 1994). These observations of asymmetry led us to make all comparisons described below using measurements from the
left side of the capitulum only.
Size or Ontogenetic Efsects.-To test for possible effects of barnacle size on the relative
amount of area covered by the carina and scuturn, we compared groups of the smallest and
largest barnacles. We compared a group of 13
small 0. anguhtu (- capitular length = 2.24
mm, SD = 0.07, range = 2.14-2.29) to a
group of 17 large 0. angulatu (- capitular
length = 3.11 mm, SD = 0.16, range =
3.00-3.43), and a group of 17 small 0. car
( - capitular length = 1.77 mm, SD = 0.12,
range = 1.43-1.85) to a group of 15 large 0.
car (- capitular length = 2.75 mm, SD = 0.15,
range = 2.57-3.00), using the KolmogorovSmirnov two-sample test. The percentages of
areas of the capitulum covered by the carina
in the large and small 0. anguhtu, and in the
large and small 0. car were not significantly
different. The percentages of areas of the capitulum covered by the scutum in the large
and small 0. angulutu also were not significantly different, but large 0. car showed significantly larger percentage coverage of the
capitulum by the scutum than did the small
0. car (P < 0.05). This latter observation suggests that the various plate configurations and
shapes that are typical of each species may,
at least in some cases, be a result of differential growth rates of the plates and the capitulum, which in turn emphasizes the im-
Mi%l
SD
cv
68.01
5.96
21.28
21.25
5.29
2.20
6.57
7.90
7.18
36.91
30.87
28.99
portance of using relatively homogeneous
samples of similar-sized adults to represent
each species when making interspecific comparisons.
Interspecific Comparisons
Octolasmis angulata and 0. car.-Relatively
large samples of 0. angulata (65) and 0. car
(61) obtained from the same gill chamber of
a single crab (Jeffries et al., 1991) provided
the opportunity to examine levels of variation
in our measurements and to make statistical
comparisons between the two species. For 0.
angulatu and 0. car, Table 2 provides the
ranges and standard deviations of the percentage of the capitular perimeter supported by
plates, and for the percentage area of the capitulum covered by the carina, the scutum,
and the two plates combined. In all of these
percentages, 0. angulata and 0. car differ
significantly from each other (KolmogorovSmirnov two-sample test, P < O.OOl), and 0.
car is the more variable of the two species in
these characteristics. For example, the coefficients of variation for the percentage of capitular coverage by the scutum for 0. angulatu
and 0. car were 18.4 and 30.9, respectively.
Multiple Species Comparisons
Plate Areas.-The
percentages of capitular
surface covered by the carina, scutum, and
tergum for 28 species of Octolasmis and one
species of Lepas are presented in Fig. 2. For
purposes of comparison, the 29 Octolasmis
(28 species with 0. angu2atu present twice)
were ranked in ascending order according to
the percentage of total plate coverage of the
capitulum. Within the 28 species of Octolasmis, this percentage of coverage ranged from
about 7% in 0. bullata to 71% in 0. tridens.
For comparison, Lepas ansergera from Thailand represents the extreme, where plates
cover the entire capitulum.
The contribution that each plate makes to
the total percentage coverage varies among
.
VORIS AND JEFFRIES: CAPITULAR
.= % PERIMETER
PLATES IN OCTOLASMIS
221
SUPPORTED
100
0
Fig. 2. The mean percentage of the left capitular area covered by the carina, scutum, and tergum is shown for 28
species of Octolasmis and Lepas anserifera. Octolasmis angulata is represented by two samples. The species are listed
in ascending order of percentage of plate coverage. Measurements (rnrn) on species designated with an asterisk were
taken from drawings based on whole-mount slides.
species. The percentage coverage by the carina ranges from zero in 0. bullata to 17 in
0. orthogonia. The coverage by the scutum
ranges from 5% in 0. gray ii to 48% in 0.
tridens, and the coverage by the tergum is zero
in several species that lack the tergum entirely
(e.g.,O. angulata, 0. bullata, and 0. cor), and
as much as 22% in 0. americanum.
of the capitular area covered is low, the peripheral position and narrow shape of the
plates provide high levels of support. For example, the percentage of the capitular area covered is as low as 7% in 0. bullata and 9% in
0. angulata (slide mounts), whereas the percentage of the perimeter supported for these
two species is 79 and 51 %, respectively.
Perimeter Supported.- The percentage of the
capitulum perimeter that is supported by
plates is presented for each species in Fig. 2.
This percentage was as low as 43% in 0. collare and complete (100%) in four species: 0.
dawsoni, 0. orthogonia, 0. indubia, and 0.
hoeki. Although there is a correlation (r =
0.69, P < 0.001) between the percentage of
the perimeter supported and the percentage of
total plate area, it is noteworthy that the percentage of the perimeter supported does not
fall below 43% among the species studied.
This is because, even when the percentage
Coefficients of Variation.- The degree of intraspecific variation that occurs in plate shape
and size differs from species to species and
may reflect the intensity of natural selection on
these structures. There is a significant inverse
correlation (r = -0.70, p < 0.001) between the
percentage of the capitulum covered by plates
and the size of the coefficient of variation (Fig.
3). These results support the prediction that
selection on the amount of plate coverage and
perhaps the amount of support required is more
relaxed among those species with relatively
smaller plates.
222
JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 17, NO.2,
1997
~
::)
-.J
::)
t:
0..
«
O
u..
O
w
(!J
~
w
>
0
o
~
Fig. 3. The mean percentage of the left capitular area covered by capitular plates and its coefficient of variation are
given for 28 species of Octolasmis. The species are in ascending order according to percentage of plate coverage.
Literature Data.- Table 3 provides capitular
support and plate area percentages on nine additional species of Octolasmis. These percentages are based on measurements made on
individual drawings found in the literature.
Although it is worth noting that all the percentages observed in this group fall within the
ranges set by those taxa that we measured
(Figs. 2, 3), the fact that these data are based
on single drawings made by other investigators means that they are not directly comparable to our own data.
Table 4 presents a list of all species of Octolasmis in alphabetical order for which we
made original drawings and measurements
(Table I) as well as those based on drawings
from the literature (Table 3). For each species,
its host category, its location on the host, and
the usual water depth of the host are provided.
DISCUSSION
In Fig. 4, 28 species of Octolasmis are ordered, according to the mean percentage of
the left capitular area covered by the capitular plates. The shading of the bars designates
those species that are usually found in crustacean gill chambers (black), always found on
the external surface of crustaceans (black
with pattern), or on hosts for which there is
some qualifying circumstance (white with
pattern). Figure 4 suggests a strong but not
absolute relationship between mean percentage of plate coverage and location on the
host. Species that live their adult lives within
the gill chambers of decapods have low percentages (7% for 0. bullata) to intermediate
(30% for 0. brevis) of their capitula covered
by plates. Those species that live on the exposed external surfaces of their crustacean
hosts have relatively high percentages (43%
and 71% for 0. warwickii and 0. tridens, respectively) of their capitula covered by plates.
Thus, the prediction that plates will cover
more area of the capitulum in species that live
on externally exposed sites, compared to species living hidden inside gill chambers, is ten-
VORIS
AND
JEFFRIES:
CAPITULAR
PLATES
IN
223
OCTOLASMIS
Table 3. Comparable data taken from the literature for nine additional species of Octolasmis. The capitular length
and width measurements (mm) of the specimens are taken from literature sources. The percentages are based on
measurements (mm) made on single published illustrations of either the left (L) or right (R) sides.
Specimen
Species of Ocrolasmis
0.
0.
0.
0.
0.
0.
0.
0.
0.
alata (R)
bathynomi (L)
iloiloensis (L)
nierstraszi (L)
pellucida (R)
sinuata (R)
trigona (R)
tydemani (L)
versluysi (L)
Capitular
length
Pementages
Capitular
width
Capitulum
supported
i::
i:;
1.:
2’6
2’3
100.0
100.0
87.5
E
2:5
1.8
5.9
2:9
if3
0:8
3.6
80.8
89.3
89.3
100.0
94.1
Carina
area
Tergum
area
TOtal
plate area
39.0
43.7
26.9
16.2
11.8
18.4
19.2
21.0
13.4
10.2
10.7
16.5
8.5
!5
lo:o
16.5
13.8
61.8
67.1
61.3
55.7
27.6
24.2
31.3
47.9
38.8
11.0
5.1
21.2
18.6
7.5
6.4
10.7
14.9
16.5
tatively supported by an array of species. We
surmise that the plates afford significant protection from predation and abrasion for those
species that live on exposed surfaces.
from drawings
Scutum
,
area
Literature
source
Aurivillius, 1894
Annandale, 1909
Rosell, 1967
Hoek, 1907
Darwin, 185 1
Aurivillius, 1894
Aurivillius, 1894
Hoek, 1907
Hoek. 1907
The coefficients of variation of the mean
percentage of the capitulum covered by all
plates provide further support for this interpretation. If total plate coverage of the ca-
Table 4. Host category, location on host, and water depth of host gleaned from the literature for 37 species of Octolasmis. Those species in permanent whole mount slides are indicated by an asterisk.
Host category
Location
on host
Depth
Reference
0.
0.
0.
0.
0.
0.
alata
americanum
angulata
antiguae
aperta
aymonini
decapods
unknown
decapods
decapods
decapods
decapods
gill chamber
unknown
gill chamber and mouthparts
gill chamber
gill chamber
gill chamber
shallow
deep(>300m)
shallow
shallow
shallow
deep+300 m)
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
bathynomi
brevis
bullata*
californiana
carpilii*
clavula
collare*
car
dawsoni
forresti
geryonophila
grayii
hawaiense
hoeki
iloiloensis
indubia
lowei
miilleri
neptuni
nierstraszi
orthogonia
pellucida
scuticosa
sinuata
tridens
isopods
decapods
decapods
decapods
decapods
decapods
decapods
decapods
isopods
decapods
decapods
sea snakes
decapods
decapods
decapods
decapods
decapods
decapods
decapods
horny coral
horny coral
sea snakes
decapods
decapods
decapods
deep (>300
shallow
shallow
shallow
shallow
shallow
shallow
shallow
deep (>300
shallow
deep (>300
shallow
deep (>300
shallow
shallow
deep (~300
shallow
shallow
shallow
shallow
deep (>300
shallow
shallow
shallow
shallow
0.
0.
0.
0.
0.
0.
trigona
tydemani
uncus
versluysi
warwickii
weberi
decapods
animate
decapods
unknown
decapods
horny coral
pleopods
gill chamber
gill chamber
gill chamber
protopodite of cheliped
maxillipeds
gill chamber and moutbparts
gill chamber
pleopods
gill chamber and mouthparts
gill chamber
body and paddle tail
gill chamber
gill chamber and mouthparts
gill chamber
mouth parts
gill chamber
gill chamber
gill chamber
stems and branches
stems
body and paddle tail
antenna and mouthparts
gill chamber
gill chamber, mouthparts,
and carapace
gill chamber
external
gill chamber
unknown
carapace and appendages
stems
shallow
shallow
shallow
shallow
shallow
deep(>300m)
m)
m)
m)
m)
m)
m)
Aurivillius, 1894
Pilsbry, 1907
Aurivillius, 1894
Stebbing, 1895
Aurivillius, 1894
Lessona and TapparoneCanefri, 1874
Annandale, 1909
Pearse, 1947
Aurivillius, 1892
Newman, 1960
Rosell, 1967
Hiro, 1936
Jeffries, Voris, and Yang, 1988
Aurivillius, 1892
Causey, 1960
Pilsbry, 1907
Pilsbry, 1907
Darwin, 1851
Pilsbry, 1907
Wells, 1966
Rosell, 1967
Newman, 1961
Darwin, 1851
Coker, 1902
MacDonald, 1869
Hoek, 1907
Darwin, 185 1
Darwin, 185 1
Hiro, 1939
Aurivillius, 1894
Aurivillius, 1894
Aurivillius, 1894
Hoek, 1907
Pearse, 1947
Hoek. 1907
Gray,’ 1825
Hoek, 1907
224
JOURNAL OF CRUSTACEAN BIOLOGY, VOl
17,NO.2, 1997
80
~
:)
-.J
:)
!=
Coo
«
()
u..
O
w
~
60
inside
gill chamber
40
~
w
6
()
20
~
0
Fig. 4. The mean percentage of the left capitular area covered by the capitular plates is shown for 37 species of
Octolasmis (see Table 1). The species are listed in ascending order of percentage of plate coverage. For each species of Octolasmis, the usual location on its host (Table 4) is indicated by shading. The intermediate condition,
"qualifying circumstances," refers to a variety of situations that are elaborated in the discussion.
pitulum is less important to species that live
in protected situations, plate variability would
be expected to rise as a result of relaxed selection. The relationship found between coefficients of variation and the mean percentage of the capitulum covered by plates supports this interpretation. In fact, we have
observed an 0. miilleri and an 0. neptuni
both lacking a tergum on one side, and another 0. miilleri and three 0. neptuni lacking both terga.
Thirteen of the 28 species depicted in Fig.
4 are designated as having a qualifying circumstance associated with their host. For example, 0. gray ii is among those species that
have the least plate coverage (11.7%), although it liyes exposed on the external surface of its host. However, it lives only on
highly venomous sea snakes. We propose that
the nature of these hosts may deter predators
and thus reduce the selective pressure for
larger plates. On the other hand, 0. gray ii
may well be exposed to abrasion because of
the nook and cranny feeding behavior of sea
snakes, and this would argue for selection
pressure in the other direction.
Octolasmis weberi and 0. orthogonia with
intermediate levels of plate coverage (34.8%
and 41.5%, respectively) (Fig. 4) live on the
exposed surface of horny corals and may derive safety from predation because of the nematocysts of the corals, and protection from
abrasion because of the sedentary habit of the
corals. Octolasmis carpilii is another species
with low plate coverage (14.8%) that lives on
the external surface of its host, but it has been
found only on the base of the cheliped of a
decapod, a site of considerable protection
from both predation and abrasion. Octolasmis
aymonini (18.2% plate coverage of the capitulum), 0. dawsoni (from isopod pleopods;
25.9% coverage), 0. geryonophila (27.7%),
0. hawaiense (53.1 %), and 0. indubia (on
mouthparts of Scyllarides squamosus (Milne-
VORIS
I
7
.
.
‘.
AND
JEFFRIES:
CAPITULAR
Edwards): 59.7% coverage) are from hosts
that came from deep water (>300 m) well below the photic zone. We surmise that deep
water affords safety from many visual predators, but may afford little or no protection
from abrasion in cases where the barnacle is
located on the mouthparts of the host.
Thus, many of the species that do not
clearly fall into the first two categories of exposure-plate relationship
(more exposure/
more plate coverage versus less exposure/less
plate coverage) may, in fact, be protected or
sheltered by some other means. Other factors,
of which we have only a rudimentary understanding, may also have confounding effects
on establishing simple relationships. For example, species of Octolasmis living within
gill chambers and protected from predation
and abrasion may nonetheless be subjected to
considerable current turbulence, thus requiring more support and hence more plate coverage. Only further detailed research can resolve the importance of these and other,
presently unrecognized, special circumstances.
At this point it is important to recognize
some of the limitations that affect this study.
First, the sample of species of Octolusmis and
the specimens chosen to represent them were
not random or exhaustive, but largely dependent on availability. Second, the methods of
measurement employed were limiting. The
lateral surface of the capitulum of Octolusmis
is generally convex, not flat. The convexity
is pronounced near the carinal margin where
the single carina is located, and thus small
differences in the viewing plane can generate large differences in the amount of the carina in view and hence the measurement of
its area. This source of variation due to technique alone should be eliminated in future
work, because it likely obscures more subtle
sources of individual variation that may be’
biologically interesting.
Nonetheless, we have moved beyond speculation regarding the relationships among the
functions and variability in plate coverage of
the capitula of Octolasmis, to a quantified
data base on which to direct and build future
research. It should also be noted that the quantitative investigation of variation in plate size
and capitulum coverage has important implications for future studies of taxonomy of a variety of pedunculate cirripedes, where capitular plate information has been used in the past
(Newman, 1967; Newman et al., 1967).
PLATES
225
IN OCTOLdSMIS
ACKNOWLEDGEMENTS
/ We thank the National University of Singapore (NUS)
and the Phuket Marine Biological Center (PMBC) for
their logistical support and for the use of their facilities
over several years, In particular, we are grateful to Mrs.
Yang Chang Man, Miss Lua Hui Kheng, Mr. Keng Loo
Yeo, Mrs. Simon Greasi, and Mr. Kelvin Lim for assistance and support at the Zoological Reference Collection at NUS. At the PMBC we owe special thanks to Mr.
Sombat Poovachiranon, Mr. Boonchoy Kuoyratanakul, a
fisherman who collected most of the crabs, and Mr.
Saengdee Chailert who received crabs from fishermen for
us. We also appreciate the skilled assistance of numerous Dickinson College students, especially Amy Hewitt,
Keow Thavaradhara, Peter Lovell, and Melinda Anderman. Support from the Dickinson College Faculty Research Fund and the Field Museum of Natural History
made this investigation possible. We greatly appreciate
the extensive comments on the manuscript by Helen
Voris. We thank the following colleagues for the loan of
specimens from their respective institutions: Danielle Defaye, Museum National d’Histoire Naturelle, Paris; Diana Jones, Western Australia Museum, Perth; Dietmar
Keyser, Zoologisches Institut und Zoologisches Museum,
Der Universitiit Hamburg, Hamburg; Eric Lazo-Wasem,
Division of Invertebrate Zoology, Peabody Museum of
Natural History, New Haven, Connecticut; Karen Reed,
Department of Invertebrate Zoology, National Museum
of Natural History, Smithsonian Institution, Washington,
D.C.; Gary Rosenberg, Academy of Natural Sciences of
Philadelphia, Philadelphia, Pennsylvania; John W. Short,
Cmstacea Section, Queensland Museum, South Brisbane,
Queensland, Australia; Karin Sindemark, Department of
Invertebrate Zoology, Swedish Museum of Natural History, Stockholm; and Shigeyuki Yamato, Seto Marine Biological Laboratory, Kyoto University, Shirahana,
Nishimuro, Wakayama, Japan.
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RECEIVED:
ACCEPTED:
8 June 1996.
8 October 1996.
Addresses: (HKV) Department of Zoology, Field Museum of Natural History, Chicago, Illinois 60605, U.S.A.;
(WBJ) Department of Biology, Dickinson College,
Carlisle, Pennsylvania 17013, U.S.A. (e-mail:voris@
fmppr.fmnh.org)