Morphological analysis of Nautilus pompilius. In: Hayasaka, S. (ed.) Marine ecological studies on the habitat of Nautilus pompilius in the environs of Viti Levu, Fiji

Abstract

Based on the two population samples from the Suva and the Pacific Harbour areas, Viti Levu Island, Fiji Islands, morphological variation and relative growth of soft and hard tissues of Nautilus pompilius were analyzed. In both samples development of gonad begins at the stage of more than 130 mm in shell diameter. Soft tissue, gonad and shell of mature males are usually heavier and larger than those of mature females. Shell form ratios are slightly different between sexes, and most mature males have broader and higher whorl apertural area than females. Morphological comparison of the two samples with that from the Philippines shows a fairly large
geographical variation not only in size and weight of the mature animals but also in the nepionic size between the two separated habitats.

Full text

Title MorphologicalAnalysisofNautiluspompilius
Author(s) TANABE,Kazushige;HAYASAKA,Shozo;TSUKAHARA,
Junzo
Citation 南方海域調査研究報告=OccasionalPapers,4:38-49
IssueDate 1985
URL http://hdl.handle.net/10232/15858
http://ir.kagoshima-u.ac.jp

Kagoshima Univ. Res. Center S. Pac..Occasional Papers, No. 4. p. 38-49, 1985
3. Morphological Analysis of Nautilus pompilius
by
Kazushige Tanabe1', Shozo
Hayasaka2'
and Junzo
Tsukahara31
Abstract
Based
on the two population
samples
from
the Suva and the Pacific Harbour areas, Viti
Levu
Island, Fiji Islands, morphological variation and relative growth of soft and hard
tissues
of
Nautilus
pompilius
were
analyzed.
In
both
samples
development
of
gonad
begins
at the
stage
of
more
than
130
mm
in
shell
diameter.
Soft
tissue,
gonad
and
shell
of
mature
males
are
usually
heavier
and largerthan
those
of
mature
females.
Shell
form
ratios are slightly
different
between
sexes,
and most mature males have broader and higher whorl apertural area than
females.
Morphological comparison of the two
samples
with that from the Philippines
shows
a fairlylarge
geographical
variation not only in
size
and
weight
of the
mature
animals
but also in the
nepionic
size between the two separated habitats.
Introduction
Following the description of trapping
experiments,
results
of laboratory work on the
morphologic variation and allometric
growth
of softand hard
tissues
in the
samples
from
the
Suva
and the
Pacific
Harbour
areas
are
given
below
with
special
reference
to the
sexual
dimorphism.
Moreover,
the
measurement
data on the Fijian
samples
were
compared
with
those
on the
Philippine
ones
(Hayasaka
et
al,
1982)
to
discuss
the
geographical
variation
of
shell
size
in
nepionic and mature stages.
Materials
and
Methods
Materials
Measurementdata of all specimenscaptured (Record of Trapping Experiment, tables 3-4 in this
volume)
were
analyzed for understanding the variation of fundamental shell morphology and the
allometric relationship between the weights of soft and hard tissues. Shells of selected 23
specimenscaptured from the Suva area in this project (SV 5-3.
12-1,
13-1-6, 13-8-14,
13-16,
13-18-
19,
14-1-5)
and of
five
additional
specimens
(four
males
(F
35,
37-38,42)and one
female
(F
42)}
captured by
Hayasaka
and Shinomiya in
1981
(Hayasaka
and Shinomiya,
1982,
fig.
1)
from
1) Department of Earth
Sciences,
Faculty of
Science,
Ehime
University.
Matsuyama
790, japan.
2)
Institute
of
Earth
Sciences,
Faculty
of
Science,
Kagoshima
University,
Kagoshima
890,
Japan.
3) Department of
Biology.
Faculty of
Science.
Kagoshima
University,
Kagoshima
890,
Japan.

39
Tanabe et
al.;
Morphological Analysis of Nautilus pompilius
almost
the
same
area
as
the
one
mentioned
above
were
used
for
individual
relative
growth
analysis
of
radius
vector
in
median
section.
Aside
from
the
seven
immature
specimens
(SV
13-4,
5,
11,
12,
16,
14-2
and F
42),
shells
of the
remaining
21
specimens
were
also
examined
for the
ontogenetic
change
of
shell
form
ratios
in
cross
section.
Weight
data of
sexual
organs
in
selected
specimens
given
by
Tsukahara
(1985,
table
1)
are
cited
in this
paper.
In
addition
to
the
specimens
from
Fiji
Islands,
shells
of
nine
specimens
collected
by
Hayasaka
and others
from
Tanon Strait, the Philippines in
1981
(B
3-6,
18,
23,
25,
41
and 52;
see
Hayasaka et al.,
1982,
fig.
3 and
table
10
for
their
detailed
locations
and
biological
data)
were also used in this paper.
Methods
Field
methods
have
already
described
in
the
earlier
chapter.
For the
analysis
of
individual
relative
growth
and
variation
of
shell
form
radius
vector
of a
spiral
(R),
nepionic
size
(=
shell
diameter
at theendof the
nepionic
constriction)
anda
last-formed
septal
thickness
were
measured
on the
median-sectioned
specimen
with an aid of a
profile
projector
(NIKON,
V-12)
attached to
a digital
micrometer
(accuracy
1
p.m).
The
former
character
was
measured
at intervals of
45°.
In
this
paper
an
adaptical
end
of
caecum
was
adopted
asan
origin
ofthe
coordinate
axes
for
growth
analysis
(the
reason
is to be
described
in the
text).
After
having
measured
the
above
characters,
most
median-sectioned
shells
were
further
cut perpendicular along the
0°-180°
line.
Shell
diameter
(D),
whorl
breadth
(B)
and
height
(H), half
length
of
umbilicus
(C) and flank
Fig.
1.
Basic
morphology,
orientation
and
measurements
of
the
shell
of
N.
pompilius
in
median
(left) and cross (right) sections.

Kagoshima
Univ.
Res.
Center
S. Pac,
Occasional
Papers.
No.4,
1985
40
position
(F)
were
measured
on
the
"half"
cross
section
at
intervals
of
180
by
means
ofa
profile
projector.
Based
on
these
measurements,
the
following
four
parameters
proposed
by
Raup
(1966)
and
Chamberlain
(1976)
were
calculated
;
thus
(1)
Whorl
expansion
rate
(W)
(=
(Rn/Rn-l)2],
(2)Distance
of
the
whorls
to
the
coiling
axis
(D)
(=
C/R),
(3)
Relative
whorl
thickness
(S)
(=
B/
H),
and
(4)
Flank
position
(FR)
(=
F/D).
Among
these
parameters,
W
reflects
whorl
inflation,
while
D
means
the
relative
size
of
umbilicus.
S
and
F
characterize
the
fundamental
whorl
shape.
Basic
morphology
and
measurements
in
median
and
cross
section
are
diagrammatically
illustrated
in
Fig.
1.
Biometrical
analysis
of
the
measurements
was
made
on
a
desk
computer
(NEC
PC-9801 F).
7
%
6
B
• •
5
FIJ
I•
4O
FEMALE
(N«23)
°»-
••
3
•
MALE
(N-13)
•
SEX
UNKNOWN
(N-1)
•
oif> •
2
1
01
«__l
1 O
OJ*.
Q 1 1 1 1
a
<
z:
O
cs
15
I 10
CD
100
110
SHELL
120
130
140
DIAMETER
(D)
FIJ
I
O
FEMALE
(N=23)
•
MALE
(N=13)
•
SEX
UNKNOWN
(N=1)
J_
90
100
110
120
130 140
SHELL
DIAMETER
(
D)
-L-
_U
••
•
o
f.
•
cP
Fig.
2.
Scatter
plots of gonad
weight
(A) or
gonad
index
(B)
versus
shell
diameter
for
selected
specimens
captured
from
the
Suva
and
Pacific
Harbour
areas,
Viti
Levu
Island,
Fiji
(August-
September,
1983).
Gonad
index
is
the
ratio
of
testis
or
ovary
weight
to
total
soft
tissue
weight.

41 Tanabe et
al.;
Morphological Analysis of Nautilus pompilius
Sexual
Dimorphism
As we could capture various-sized
Nautilus
from the areas studied, allometric relationships
of a shell and soft tissue were further examined in relation to sexual maturity.
The average relative growth of wet gonad (ovary or testis) weight versus shell diameter in the
selected specimens from Suva and Pacific Harbour areas (Fig. 2 A) shows that in females ovary
weight increases exponentially as shell diameter exceeds 120mm and attains to a maximum at the
stage around 140mm in shell diameter. In contrast to this, full development of testis in males is
prolonged to the stage between 140-150 mm in shell diameter. Therefore, at the stages between
120-140 mm in shell diameter gonad weight in females is slightly larger than that of the males of
similar shell size. Most specimens at the stages larger than 140mm in shell diameter are males.
Testis in full-grown males appears to be much heavier than ovary in mature females.
Scatter plots of gonad index (ovary or testis weight/soft tissue weight) versus shell diameter
(Fig. 2 B) also suggest that gonad in both males and females increases exponentially through the
stages larger than 130-140 mm in shell diameter. If a provisional standard of sexual maturity is
i
o
ID
111
D
CO
CO
500
g
400
FIJ
I
(SUVA
AND
PACIFIC
HARBOUR
AREAS)
o
Female
N=
15
•Male
N=54
•
Sex
unkown
N=1
300
o
CO
200
100
_1_
J_
JL
80
90
100
110
120
130
SHELL
DIAMETER
_1_
140
150
160
mm
Fig. 3. Scatter plots of soft
tissue
weight
versus
shell diameter for
selected
specimens
from the
Suva and Pacific Harbour areas. Curve fits by eye.

Kagoshima Univ. Res. Center S. Pac. Occasional Papers, No. 4,
1985
42
regarded to be 3.0 on gonad index, mature males are mostly larger than mature females.
Also, in the specimens larger than 140mm in shell diameter, males usually possess a heavier
soft tissue than females (Fig. 3). Such a sexual dimorphism expressed by the shell size or body
weight has already been confirmed by us in the samples of Nautilus pompilius from Tafion Strait,
the Philippines
(Hayasaka
et al.
1982)
and N. cf.
pompilius
[= N. belauensis
Saunders,
1981)
from Palau
(Saunders
and
Spinosa,
1978).
Biometrics
of
Shells
Ontogenetic allometry
It has already been demonstrated that the growth of a spiral of many chambered cephalopod
shells can be approximated by the following equation :
R = aeKH
where R and ® are a radius vector and a total rotation angle from the coiling axis respectively,
and a is a constant
(Moseley,
1838; Thompson, 1917;
Huxley,
1932;
OBATA,
1959,1960).Hi-
Table I. Statistical data for the radius vector in the sample of
Nautilus
pompilius
from
off
Suva
Harbour.
Viti
Levu
Island, Fiji Islands (male plus
female).
Staged)
N
X+t0.05SE
(mm)
s(mm)
V
Observed
range
(mm)
0.25
28
1.80+0.19
0.50
28
5.75+0.22
0.75
28
8.97+0.17
1.00
28
10.16+0.12
1.25
28
9.76+0.14
1.50
28
8.86+0.13
1.75
28
8.84
+
0.14
2.00
28
10.10+0.17
2.25
28
13.02+0.28
2.50
28
17.38+0.35
2.75
28
22'.00
+
0.37
3.00
28
25.26+0.31
3.25
28
26.85+0.34
3.50
28
28.28+0.42
3.75
28
30.65+0.50
4.00
28
35.12+0.64
4.25
28
41.75+0.80
4.50
28
50.25
+
1.04
4.75
28
60.51
±1.24
5.00
28
70.07
+
1.30
5.25
26
78.92+1.52
5.50
14
85.74
+
2.59
0.49
27.21
0.57
10.00
0.43
4.78
0.31
3.06
0.37
3.76
0.34
3.82
0.36
4.11
0.44
4.35
0.72
5.55
0.90
5.18
0.96
4.37
0.80
3.16
0.88
3.29
1.07
3.80
1.28
4.17
1.65
4.71
2.06
4.94
2.69
5.36
3.20
5.30
3.36
4.80
3.77
4.77
4.49
5.24
1.1-
-
2.9
4.4-
-
6.5
8.0-
-
9.6
9.5-
10.8
9.1-
-10.6
8.3-
-
9.9
8.3-
-
9.5
9.2-
-11.0
11.2-
-14.4
15.8-
-19.0
19.7-
-23.5
23.5-
-26.4
25.0-
-28.0
26.0-
-29.9
29.4-
-32.8
31.0-
-37.9
38.1
-45.9
44.4-
-54.9
52.1-
-65.2
61.8
-75.0
70.0-
-85.6
72.4-
-98.7

43
Tanabe et
al.;
Morphological
Analysis
of
Nautilus pompilius
rano
(1977),
Hirano
and
Obata
(1979)
and
Hirano et al.
(1980)
applied
the
above
equation
to
express
the
growth
of a
radius
vector
in
Nautilus
pompilius
and N.
macromphalus.
These
authors
set
a
coiling
axis
at a
center
of
the
inscribed
circle
in
the
umbilical
perforation.
The
umbilical
perforation
in
Nautilus
is,
however,
not
an
initial
portion
of
shell
growth
unlike
a
protoconch
of
ammonites
and
gastropods,
but is
formed
after
the
completion
of the
first
whorl.
For
this
reason,
we
used
an
adaptical
end
ofa
caecum
asan
initial
partof
whorl
growth
(Fig.
1).
Statistical
data for
growth
of
radius
vector
in the
specimens
examined
are
listed
in
Tables
1-3.
Coefficients
of variation are
relatively
small
in the
specimens
examined,
other than the
case
in the
earliest
stage.
As
shown
in
Fig.
4,
the
growth
pattern
of
radius
vector
can
not
be
expressed
by
a
single
allometric
equation. A
conspicuous
decrease
of radius
vector
near the end of the
first
whorl
is
observed,
and
this
probably
owes
to a
decline
of
whorl
growth
associated
with
a
formation
of a
nepionic
constriction.
In
the
stage
after
the
second
whorl
the
slope
of
allometric
shell
growth
in
males
seems
to be
slightly
larger
than that of
females,
but the
means
of radius
vector
of
males
and
females
at
the
same
total
rotation
angle
do
not
show
any
statistically
significant difference.
Ontogenetic changes in shell form
The
results
of this
analysis
may
be
concisely
summarized
in the S-W and D-FP
scatter
diagrams
in
Fig.
5. The two
series
of
scatter
diagrams
show
that the variation of
shell
form
gradually
decreases
with
growth.
At the
stages
of
2.5
nand 4.5 n,
males
and
females
do not show
a
significant
difference
in
shell
form,
but
at
5.5
n
stage
(probably
mature
or
almost
mature
stage)
males
have
larger
W and S
values
than
females.
This
fact
correlates
well
with
the
growth
of
soft
tissue
weight
(Fig.
2),
and
both
data
postulate
that
in
mature
or
almost
mature
stage
body
chamber
Q25
Q5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25 3.5 3.75
TOTAL
ROTATION
ANGLE
4.25
4.5
4.75
5.25
5.5^
Fig.
4.
Semi-logarithmic
diagram
showing
the
ontogenetic
growth
of
radius
vector
versus
total
rotation angle for
selected
twenty-eight
specimens
from
the Suva area. Horizontal line and
black or white rectangles indicate the arithmetic mean and twice of standard deviation.

Kagoshima Univ. Res. Center S. Pac, Occasional Papers, No. 4,
1985
volume or weight of males is usually greater than those of females.
44
Growth of the last septum thickness
The relationship between the last septum thickness and the body chamber length was
examined in the twenty-eight median-sectioned
specimens
from the Suva area. Except for
ri\Q
young specimens, all specimens have already attained to secret a final septum, judging from
closing together of the last two or three septa. As shown in Fig. 6, in the specimens of less than
110
mm shell diameter the last septum gradually thickens with the increase of body chamber
length. The septum attains to a full thickness (ca.
1.2-1.3
mm) when body chamber reaches to
115
in spiral angle. Fig. 6 also
suggests
that the growth of body chamber
(=
length of outer shell wall
and volume of soft tissue) has been continued after the completion of the last septum. In this
figure
amounts of cameral liquid within the last chamber are also shown near the plots of
selected
thirteen
specimens
(ml unit). The relationship
between
the relative thickness of the last septum
and the amount of liquid in the last chamber for the eleven specimens are shown in Fig. 7. In the
specimen, SV
12-3
with a very thin, incomplete last septum (0.06mm in thickness; about 9 % of
the thickness of the preceeding septum), the
newest
chamber is completely filled with liquid. In
5.5
*
<
CC
2
o
co
2
<
Q_
X
111
CC
O
I
3.0
2.5
0.7
4.8 •
4.5
0.8
4.5*
2.5*:
.*
I
0.9
0.8 0.9 1 1.1 12
S (
RELATIVE
WHORL THICKNESS)
LEGEND
•MALE
o
FEMALE
X
< 0.10
5.5*
COILING
JO
o
o
•
•o
• •
• • o
III
I
<*
•
•
P o 1,
CO
_J
CC
O
^
0.10
HI
X
4.5^
0.3
0.4
0.5
2.5*
0.10
•
•
•
&o o
•
0.05
• • •
••
o•
fp
• • •
01
0. 3
0.4
0.5
FP(FLANK
position)
Fig.
5.
Two
series
of
double
scatter
plots
of
Raup's
(1966)
parameters
of
shell
forms
for
selected
specimens
of N.
pompilius
from
the
Suva
area,
showing
the
ontogenetic
changes
of
shell
morphology between males and females.

45 Tanabe et
al.;
Morphological Analysis of Nautilus pompilius
the specimens, SV 10-6, 13-4 and 13-18 with an intermediate last septal thickness (ca. 20-70%
of the total thickness of the preceeding septum), about 20-30% of the final chamber has already
been emptied. After having attained to a maximum septal thickness, several specimens still possess
small amounts of liquid (about 5 -25 %of a chamber volume) within their last chamber. However,
in the specimens with a body chamber longer than
120°,
the last chamber has almost been emptied.
These observations provide the following conclusions: (1) first emptying occurs long before the
completion of the last septum, (2) growth of body chamber and a gradual pumping of cameral
liquid have been continued after the last septum has reached its maximum thickness. Fig. 7 also
strongly suggests that the emptying rates gradually decrease with growth of body chamber .
Ward
et al. (1981, fig. 5) and
Ward
and
Chamberlain
(1983,fig. 3) described the relation
ship between cameral liquid volume and last septum thickness in N.
macromphalus
and
TV.
pompilius
on the basis of long-term radiographic observations of living animals in captivity.
According to their observations, in both speciesfirst emptying occurs when the last septum reaches
to 15 to 60 %of the expected final thickness. Our data apparently differ from those of
Ward
et
al. (1981) and
Ward
and
Chamberlain
(1983) in the thinner septum thickness when first
emptying occurs. The reason for this appears to be the difference in emptying patterns of animals
Table 2. Statistical data for the radius vector in the male samplesof
of
Nautilus
pompilius
from
off Suva Harbour,
Viti
Levu
Island, Fiji.
StageU)
N
X±t
0.05SE(mm)
s(mm)
V
Observed
range
(mm)
1.1-
2.9
4.5-
6.5
8.2-
9.6
9.5-10.7
9.0-10.6
8.3-
9.9
8.3-
9.5
9.3-11.0
11.2-14.4
15.3-19.0
19.7-23.5
23.4-26.4
24.7-28.0
26.0-29.9
27.7-32.8
31.0-37.9
37.2-45.9
44.4-54.9
52.1-65.2
61.8-75.0
70.0-85.6
76.8-92.0
0.25
20
1.84+0.26
0.55
29.89
0.50
20
5.82+0.26
0.56
9.67
0.75
20
9.11+0.18
0.37
4.11
1.00
20
10.19+0.13
0.29
2.80
1.25
20
9.77+0.17
0.36
3.68
1.50
20
8.87+0.17
0.36
4.08
1.75
20
8.84+0.17
0.37
4.18
2.00
20
10.15+0.19
0.41
4.06
2.25
20
13.16+0.35
0.76
5.74
2.50
20
17.57+0.42
0.91
5.15
2.75
20
22.17+0.45
0.97
4.37
3.00
20
25.38+0.35
0.74
2.93
3.25
20
26.94
±0.40
0.86
3.19
3.50
20
28.36+0.49
1.04
3.67
3.75
20
30.78
±0.59
1.26
4.09
4.00
20
35.37+0.77
1.65
4.66
4.25
20
42.14
±0.97
2.08
4.94
4.50
20
50.68
+
1.29
2.76
5.44
4.75
20
61.01 + 1.57
3.35
5.49
5.00
20
70.60
±1.60
3.43
4.86
5.25
20
79.44
±1.75
3.75
4.72
5.50
10 86.43
±3.48
4.86
5.63

Kagoshima
Univ.
Res.
Center
S. Pac,
Occasional
Papers,
No.4,
1985
46
under natural and artificial conditions.
Many
workers
have
suggested
that the cameral liquid in
living
Nautilus
has
a
primary
function
to
support
calcifying
septa
and
siphuncle
against
implosion
by
ambient
hydrostatic
pressure,
for
the
gas
pressure
within
the
chambers
never
exceeds
atomos-
pheric
pressure
regardless
of
depth
(Denton
and
Gilpin-Brown,
1966;
Collins et al.,
1980;
Ward
et al.,
1980,
1981
;
Ward
and
Chamberlain,
1983).
Therefore, drainage of cameral
liquid
must
occur
after
the
septum
attains
a
sufficient
thickness
to
withstand
the
high
hydrostatic
pressure
in the
habitat.
From
our
observation,
it
has
been
realized
that
even
a
incomplete
septum
with only 20%of the
final
thickness
can
withstand
the
pressure
of
more
than 40
atm.
Geographic Variation of Shell Morphology
It is
well
known
that
Nautilus
pompilius
is
widely
distributed in the tropical
South
Pacific.
The
Philippines
and Fiji
Islands
are
situated
in
the
northwestern
and
southeastern
margins
ofthe
wide habitat realm of this
species
(Hamada,
1977;
Saunders,
1981
b).
Based
on the two
samples
from
Tanon
Strait,
the
Philippines
and
from
the
Suva
area,
Fiji
Islands
(see
Hayasaka
Table 3. Statistical data for the radius vector in the female sample of
Nautilus
pompilius
from
off Suva Harbour, Viti Levu Island,
Fiji.
Staged) N
X+t
0.05SE(mm) s(mm) V Observed range (mm)
1.4-
2.1
4.4-
6.5
8.0-
9.1
9.7-10.8
9.1-10.2
8.5-
9.2
8.3-
9.3
9.2-10.6
12.1-13.3
16.3-17.8
20.0-22.8
24.3-25.8
25.5-27.7
26.6-29.6
29.0-32.2
32.3-36.7
38.9.-44.2
46.4-52.6
56.8-63.3
66.0-73.6
73.7-82.2
72.4-98.7
0.25
81.68
±0.22
0.26
15.31
0.50
85.58
±0.48
0.57
10.22
0.75
88.63
±0.30
0.36
4.13
1.00
810.11
±0.30
0.36
3.58
1.25
8
9.74
±0.32
0.38
3.94
1.50
88.83
±0.22
0.27
3.04
1.75
88.83
±0.29
0.35
3.92
2.00
8
9.98
±0.40
0.48
4.83
2.25
812.66
±0.39
0.47
3.72
2.50
816.90
±0.57
0.69
4.06
2.75
821.56
±0.66
0.79
3.65
3.00
824.96
±0.71
0.85
3.42
3.25
826.64
±0.76
0.91
3.42
3.50
828.09
±0.95
1.13
4.03
3.75
8
30.33
±1.06
1.27
4.19
4.00
8
34.49
±1.25
1.49
4.32
4.25
840.75
±1.38
1.65
4.02
4.50
8
49.16±1.82
2.18
4.43
4.75
859.28
±2.01
2.41
4.06
5.00
868.75
±2.33
2.79
4.06
5.25
677.20
±3.51
3.34
4.33
5.50
4
84.00
±4.32
2.71
3.23

47
D
I-
CL
W
CO
<
CO
CO
UJ
z
Tanabe et al.; Morphological Analysis of
Nautilus
pompilius
•
•'
100
105
110
115
120
LENGTH
OF
BODY
CHAMBER
125
130
Fig.6. Plots of last
septal
thicknenss
versus
body
chamber
length
for
selected
twenty-eight
specimens
of N.
pompilius
from
the
Suva
area.
The
number
beside
some
plots indicates
cameral liquid volume (ml) in the last chamber.
100%
-• •
80
-
♦
•
60
-
40
•
l• i
20
<
♦
IMMATURE
• MATURE OR
ALMOST MATURE
0• •
AMOUNT
OF
LIQUID
IN
CHAMBER
(PERCENT FILLED)
Fig. 7. Plots of relative thickness of the last septum versus amounts of liquid volume within the
last chamber (percent chamber volume) for selected specimens from the Suva area. Relative
thickness of the last septum is expressed as percentage of total thickness of the preceeding
septum for immature shells or that of the expected thickness (1.3mm) of the full-grown final
septum for almost mature shells.

Kagoshima
Univ.
Res.
Center
S. Pac,
Occasional
Papers,
No.4,
1985
48
et al.,
1982
and
Hayasaka
and Shinomiya,
1982
for
detailed
records),
Tanabe et al.
(1983)
discussed
the
geographic
variation of
several
morphological
characters
of N.
pompilius
between
the two isolated
areas.
They
concluded
that the two
samples
show
astatistically significant
difference
in the
size
and
weight
distributions in the
mature
stage.
Definition of
mature
stage
in
our previous papers
(Hayasaka
et al.,
1982
;
Tanabe
et al,
1983)
was, however, relied on the
characteristic
features
of the
shell
such
as a
presence
of a
blacked
and
thickened
aperture,
closing
together
of the
final
two or
three
septa
and a
thickening
ofthe last
septum.
In this
study,
we
also
examined a development of gonad in some
specimens.
As a result, it was realized that the mature
females
and males with a well-developed gonad have the shells of about
140
mm and
150
mm in
diameter
respectively
(Fig.
2,
B).
These
average
shell
sizes
are about 20
mm
smaller
than
those
(Hayasaka et at,
1982,
fig.
19; Tanabe et al,
1983,
table 3) of mature
males
and
females
from
Tahon
Strait,
the
Philippines.
Thus,
this
paper
provides
more
concrete
data
for
the
geographic
variation of this species in the mature
stage.
Table 4. Statistical data on the nepionic
shell
size for the samples of
N.
pompilius
from the Fiji Islands (Suva area) and the Philippines
(Tafion Strait and Bohol Strait near Siquijor Islands).
Sample N X
±t
0.05SE(mm) s(mm) V Observed range (mm)
Suva
28
31.03+1.10
2.84
9.16
24.9-35.4
Tafion
6
25.72+0.95
0.90
3.50
24.7-27.1
Bohol
i
22.95
+
2.25
0.25
1.09
22.7-23.2
In addition to the
difference
in
mature
stage,
the
present
species
shows
a
fairly
large
intraspecific
variation in the
nepionic
shell
size
between
Fiji and
the
Philippines.
As
shown
in
Table
4,the
size
ranges
from
24.9
mm
to
35.4
mm
in
the
specimens
from
the Fiji
Islands
(Suva
and
Pacific
Harbour areas); and the
mean
nepionic
shell
size
(31.0
mm
; N=
28)
is
much
larger
than
those
of the
samples
from
Tafion
and
Bohol
Straits,
the
Philippines.
From
the
oxygen
isotopic
analysis
of the
shells
Cochran
et al.
(1981)
and
Taylor
and
Ward
(1983)
suggested
that the
nepionic
constriction
in
Nautilus
is
probably
marked
at the
time
of
hatching.
If this
opinion
is
correct,
the
above
difference
in the
nepionic
shell
size
among
the
three
population
samples
indicates
the
geographic
variation
in
the
size
of
post-embryonic
young
between
Fiji and
the
Philippines.
References
Chamberlain, J.
A.
Jr.,
1976:
Flow
patterns
and
drag
coefficients
of
chambered
cephalopod
shells. Palaeontology,
19,
539-563.
Cochran,
J. K.,
Rye,
D. M. and
Landman,
N. H.,
1981
:Growth rate and habitat of Nautilus
pompilius
inferred
from
radioactive
and
stable
isotope
studies.
Paleobiology,
1,
469-480.
Collins,
D. H.,
Ward,
P. D. and
Westermann,
G. E. G., 1980 : Function of cameral water in
Nautilus. Paleobiology, 6,
168-172.
Denton, E. J. and Gilpin-Brown, J. B„
1966
: On the
buoyancy
of the pearly
Nautilus.
J.
Mar.

49 Tanabe et
al.;
Morphological Analysis of Nautilus
pompilius
Biol. Assoc. U. K., 46, 723-759.
Hamada,
T.,1977: Distribution and some ecological barriers on the habitat condition of
Nautilus
and its application to the rearing of
Nautilus
macromphalus.
Sci. Paps. Coll.
Gen.
Educ,
Univ.
Tokyo,
27,
89-102.
Hayasaka,
S. and Shinomiya, A.,
1982
: Marine ecological study on the habitat of Nautilus in
the environs of Viti Levu Island, Fiji Islands. Sci. Res. Rep.
Oceania,
(NAV '81)Kagoshima
Univ.
Res.
Center
S.
Pac,
I.
69-73
(in Japanese).
,
Saisho,
T.,
Kakinuma,
Y.,
Shinomiya,
A.,
Oki,
K.,
Hamada,
T.Janabe,
K.,
Kanie,
Y.,
Hattori,
M.,
Vande
Vusse, F.,
Alcala,
U
Cordero,
P. A. Jr.,
Cabrera,
J. J.
and
Garcia,
R.G., 1982: Field study on the habitat of
Nautilus
in the environs of Cebu
and Negros Islands, the Philippines.
Mem.
Kagoshima
Univ.,
Res.
Center
S. Pac, 3(1).
67-115.
Hirano, H.,
1977:
Biometrical
characteristics of
Nautilus
pompilius.
Gakujutsu
Kenkyu
(The
Sci. Res.),
Ser.
Biol.
Geol.,
School
of Educ,
Waseda
Univ.,
26,
13-23.
and
Obata,
I.,
1979
: Shellmorphology of
Nautilus
pompilius
and
A^.
macromphalus.
Bull. Natl. Sci. Mus., Ser. C (Geol. & Paleont.), 5,
113-130.
, and Tanabe, K. 1980: Biometric characteristics (In:
Hamada,
T., Obata,
I. and Okutani, T.
eds.,
1980)
p.
34-43.
Tokai
Univ.
Press,
Tokyo.
Huxley.
J. S., 1932: Problems of Relative Growth. 312p. Dover Publ., New York.
Moseley,
H., 1838: On the geometrical forms of turbinated and discoid shells. Phil. Trans.
Royal Soc. Lond. in
1838,
351-370.
Obata, I.,
1959
:Croissance sur
quelques
Especes
des
Desmoceratidae.
Mem.
Fac. Sci.,
Kyushu
Univ.,
Ser. D (Geol.), 9, 33-45.
, 1960: Spirale de quelques ammonites. Ibid., 9,
151-163.
Raup, D. M., 1966: Geometric analysis of shell coiling: general problems.
/.
Paleont., 40,
1178-1190.
Saunders,
W. B.,
1981
a : A new species of Nautilus from Palau. The
Veliger,
24,
1-7.
,
1981
b : The species of living Nautilus and their distribution. Ibid., 24, 8-17.
Tanabe,
K.,
Hayasaka,
S., Saisho, T., Shinomiya, A. and Aoki, K. 1983: Morphologic
variation of
Nautilus
pompilius
from the Philippines and Fiji Islands (In :
Hayasaka,
S. ed,
1983.).
Kagoshima
Univ.,
Res.
Center
S. Pac,
Occasional
Papers.,
1,
9-21.
Taylor,
B.
E. and Ward, P. D., 1983: Stable isotopic
studies
of
Nautilus
macromphalus
Sowerby
(New
Caledonia) and
Nautilus
pompilius
L. (Fiji).
Palaeogeogr.,
Palaeoclimatol,
Palaeoecol., 41, 1-16.
Thompson, D., 1917: On growth and Form. 1116 p. Cambridge Univ. Press, London.
Tsukahara,
J., 1985: Histological and histochemical studies of gonads of
Naultilus
pompilius
from Fiji (In: Hayasaka, S.
ed.,
1985).
Mem.
Kagoshima
Univ.,
Res.,
Center
S. Pac,
Occasional
Papers,
4, 50-60.
Ward,
P. D. and
Chamberlain,
J. A. Jr., 1983: Radiographic observation of chamber forma
tion cycle in Nautilus
pompilius.
Nature,
303,
57-59.
,
Greenwald,
L. and
Greenwald,
O., 1980: The buoyancy
of
the chambered
Nautilus.
Sci.
Amer., 243, 190-203.
, and
Magnier,
Y.,
1981
: The chamber formation cycle in Nautilus
macromphalus. Paleobiology, 7,
481-493.

Plates
7-9

Explanation of Plate 7
Figs.
1-3.
Median
sections
of
the
shells
of
Nautilus
pompilius
from
Suva
area,
Fiji
Islands.
1.
Early
whorls
of
specimen
SV
13-2
(male).
Scale
bar
indicates
5
mm.
Arrow
points
to a primary constriction.
2.
Specimen
SV
15-3
(female).
Scale
bar
represents
1
cm.
3.
Specimen
SV 14-3
(male).
Scale
bar
represents
1
cm.

Tanabe
et al.: Morphological Analysis
f
i
>
/
( v /
¥*
'X
\
j^i
T!l|
Plate
7
I
X

Explanation of Plate 8
Figs.
1-6.
Dorsal
views
of
the
mature
or
almost
mature
shells
of
Nautilus
pompilius
from
the
Suva area, Fiji Islands. All X2/3.
1.
Specimen
SV
13
- 3 (mature
female).
2.
Specimen
SV
5- 3 (mature
female).
3.
Specimen
SV
12-1 (almost
mature
female).
4.
Specimen
SV
14-5
(almost
mature
female).
5.
Specimen
SV
14-2
(almost
mature
female).
6.
Specimen
SV
14-3
(mature
female).

Tanabe et al.: Morphological
Analysis
Plate
lift
HHnHHP
4
Hi
lllllv:
P 1
>.••:.• .:.•::;•

Explanation of Plate 9
Figs. 1-4.
Nautilus
pompilius
from
Suva area, Fiji
Islands.
Lateral (a) and dorsal (b)
views
of
each specimen. All X 0.5.
1. Specimen SV
10-4
(immature male).
2. Specimen SV
10-3
(immature female).
3. Specimen SV
10-2
(immature male).
4. Specimen SV
10-1
(immature male).

Tanabe et al.: Morphological
Analysis
Plate
9
2a mf f
f'm*
1b
-i: pr*i>
2K
3b
od
latii
\*
r
1-
^r
¥
s/"
:»*:
IIP*
••mWti
*•.,-_,»,,,»>-.'.-«
•*SaF
4b
.
~fM!:isi^:
4a
i *
jfjM
w
: