Exploration of morphospace using Procrustes analysis in statoliths of cuttlefish and squid (Cephalopoda : Decabrachia) - Evolutionary aspects of form disparity

12 Pages·2000·6 MB·English

by  J L Dommergues

THE VELIGER
© CMS. Inc., 2000
The Veliger43(3):265-276 (July 3. 2000)
Exploration of Morphospace Using Procrustes Analysis in Statoliths of
—
Cuttlefish and Squid (Cephalopoda: Decabrachia) Evolutionary Aspects of
Form Disparity
JEAN-LOUIS DOMMERGUES and PASCAL NEIGE
Centre des Sciences de la Terre de TUniversite de Bourgogne & UMR CNRS 5561. 6 Boulevard Gabriel. F-21000
Dijon, France
AND
SIGURD BOLETZKY
V.
Observatoire Oceanologique de Banyuls, Laboratoire Arago, UMRCNRS 7628, F-66651 Banyuls-sur-Mer, France
Abstract. This paper reports on a pilot study using, for the first time, a Procrustes type analysis ofshape in exploring
the morphospace of cephalopod statoliths. A total of 12 species of cuttlefish and squid (Decabrachia) from the Medi-
terranean were analyzed, based on 18 homologous points (landmarks) chosen on the anterior statolith surface. For two
species (one cuttlefish, one loliginid squid) size ranges were sufficiently large to reveal ontogenetic trends in statolith.
Comparisons between species resulted in four well-defined sets of statolith morphology corresponding, respectively, to
(1) sepiid cuttlefish, (2) Rossia (a large sepiolid squid), (3) myopsid squids, (4) oegopsid squids and small sepiolids.
The morphological "dissociation" of large and small sepiolids suggests a relation between statolith size and shape
"distinctness," and draws attention to the possibly paedomorphic shapes at the lower end of the size scale.
INTRODUCTION Our study reconsiders the conclusion ofClarke & Mad-
dock (1988b) as to phylogenetic information provided by
Statoliths are calcareous particles that are attached to an statolith morphology, in (1) exploring morphospace pat-
epithelial receptor complex inside the paired statocysts of terns in statoliths ofseveral decabrachian groups, consid-
cephalopods. They grow by periodic addition ofaragonite ering variability at different levels from intraspecific to
layers crystallized from the statocyst fluid. They are part intergroup (family) level, (2) assessing biological form
ofthe macula/statolith system for the detection ofgravity disparity between statoliths in terms of morphological
andotherlinearacceleration. This gravityreceptorsystem distances that are testable against the phylogenetic trees
functions along with a complementary angular accelera- derived from molecular methods, and (3) identifying like-
tion receptor system, which occupies the greater part of ly homoplasies by comparing traditional taxonomy, ex-
the statocyst (Budelmaiin et al., 1997). The statolithshave ploitation ofmolecular patterns and statolith morphology.
been studied intensively since the beginning ofthe 1960's This approach should allow us to consider two evolution-
(e.g.. Young, 1960; Clarke & Maul, 1962; Lombarte et ary aspects complementary to one another, namely adap-
al., 1997). In recent years, much attention has been given tive significance versus genetic fixation of statolith mor-
to the growth layers observed in squid statoliths as po- phology.
&
tential age markers (Jereb et al., 1991; Arkhipkin Bi- Form disparity needs to be described in morphological
&
zikov, 1997; Bizikov Arkhipkin, 1997). terms applied to the disparity definition proposedby Raff
Clarke & Maddock (1988a, b) came to the conclusion (1996), according to which disparity is the measure of
that the shape ofthe statoliths depends little on theirfunc- how fundamentally different organisms are. Methods of
tion and heavily on the phylogeny. In contrast, the overall geometric morphometry (Procrustes analysis) have
structure of the statocysts apparently reflects rather proved interesting on theoretical grounds (Bookstein,
strongly the respective life style and locomotor activity 1991) and efficient in their applications to various zoo-
of a species (Young, 1988, 1989). Thus the question re- logical groups (e.g., Tabachnik & Bookstein, 1990; Laur-
mains open whether statolith form, even if it appears to in et al., 1994; Neige & Dommergues, 1995; David &
depend little on the function of the statolith (Clarke & Laurin, 1996; Neige & Boletzky, 1997). These methods
Maddock, 1988b), might nevertheless reflect some phys- are based on the utilization of anatomically conspicuous
ical constraints relatedtothe movement oftheendolymph points (landmarks sensii Sneath, 1967; Bookstein et al.,
inside the statocyst. 1985; Bookstein, 1991). A given set oflandmarks serves
Page 266 The Veliger, Vol. 43, No. 3
Table 1
Traditional classification of the studied taxa (after Mangold & Portmann, 1989), and number of individuals (n) used for
analysis.
Order Suborder Family Subfamily
SEPIOIDEA Sepiidae Sepia officinalis Linnaeus, 1758 11
Sepia elegans d'Orbigny, 1835 11
Sepia orbignyana Ferussac, 1826 11
Sepiolidae Rossiinae Rossia macrosoma (Delle Chiaje, 1829) 03
Sepiolinae Sepieila neglecta Naef, 1916 05
Sepietla oweniana (Pfeffer, 1908) 07
Sepiola sp. 01
TEUTHOIDEA Myopsida Loliginidae Loligo vulgaris Lamarck. 1798 32
Alloteuthis media (Linnaeus, 1758) 31
Oegopsida Enoploteuthidae Abralia veranyi (Riippell, 1844) 01
Ommastrephidae lllicinae Illex coindetii (Verany, 1837) 09
Todaropsis eblanae (Ball, 1844) 02
as a morphological descriptor. Comparison ofthe relative face curvature in the lateral dome (Point 17) is used, our
positions of these landmarks warrants localization and descriptor also provides some information on the relief
quantification of morphological differences between on- of the anterior face. Figure IC gives the localization and
togenetic stages, individuals, or taxa. Such a representa- assessment of the 18 landmarks as adopted in this study,
tion is called a morphospace (Neige et al., 1997); here it taking into account the terminology of Bookstein (1991).
is given in the form ofaphenogram forcephalopod stato-
Data Acquisition and Morphometric Treatment
Hths.
Homologous points, localized on camera lucida draw-
MATERIALS and METHODS ings of statoliths, were seized using a digitizer
OSPACE® DIGITIZER). The adjustments permitting
Our analysis covers nine genera: fourSepioidea, fiveTeu- form comparisons were achieved with the LSTRA algo-
thoidea (Table 1). This sample represents a wide range of rithm ofthe Procrustes program (David & Laurin, 1992).
decabrachian diversity and covers the greater part oftaxa
The phenetic trees derived from a distance matrix, cal-
s1t9u9d6i,ed19r9e7ce;ntBloyucwhiethr-mRooldeocnuila&r mBeotnhnoadusd,(B1o9n9n6)a.udAlelt talh.e, c3)u,lawteerdewiotbhtatihneedPruoscirnugsttehsepFriotcghraamlg(osreiethAmppoefntdhiexP1H,Y2-,
specimens were caught in the area of Banyuls-sur-Mer
LIP program (Felsenstein, 1990).
(western Mediterranean).
The first step of the analysis was to compare all the
individuals in pairs (Pairwise analysis ofProcrustes soft-
Landmarks
ware) within each species. In some cases, this step could
Although the statoliths of decabrachian cephalopods allow one to surmise an ontogenetic trend in statolith
show a wide variety offorms, their structure is sufficient- morphology. To test the veracity of this observation, a
ly constant to permit recognition of homologies. In our phenetic tree is established that summarizes all the pair-
study, homologies are derived from a subdivision of the wise comparisons. If such a trend is confirmed, the sam-
whole statolith in four basic compartments according to ple is represented for the following interspecific analysis
the terminology of Clarke (1978): attachment area or by two categories: one for small specimens, the other for
wing, ventral rostrum, lateral dome, and dorsal dome large ones.
(Figure lA). Nevertheless our approach of morphology To compare species, an average individual is calculated
using landmarks is different from the one chosen by (Consensus Analysis option ofProcrustes software) from
Clarke & Maddock (1988b) who took linear measure- all individuals included in the species, except in ontoge-
ments for subsequent processing by multivariate analysis. netically marked species where two average individuals
are calculated: one for small specimens, the other for
In this study, only the anterior side of the statolith is
analyzed. Apart from the fact that the attachment area, large ones.
which is one of the most important structural elements, RESULTS
is entirely exposed only on the anterior side, this side has
the advantage of showing a clear partitioning, which al- Variation within Species
lows one to recognize a large number of homologous For Loligo vulgaris, if the largest individual is com-
points (Figure IB). Since the position of maximum sur- pared with the smallest, the adult statolith appears rela-
J.-L. Dommergues et al., 2000 Page 267
Lateral dome Dorsal dome
Attachmentarea
orWing
a Wing fissure
:
b Wing shelf
:
c : Wing ventral indentation
Ventral rostrum
d Main spur
:
e Wingdorsal indentation
:
Number Type Description
1 2 Medialmost point ofwing spur
2 2 Medialmost point ofwing fissure
3 2-3 Dorsalmostpoint ofwing shelf
4 2-3 Ventralmost pointofwing shelf
5 1 Medial contact ofventral rostrum and wing
6 2 Lateralmostpoint ofwing ventral indentation
7 2 Medialmostpoint ofmain spur
8 2 Lateralmostpoint ofwing dorsal indentation
9 3 Intersection ofaparallel to the axis (5-10) and rostrummedial edge
10 2 Ventralmost pointofventral rostrum
11 3 Intersection ofaparallel to the axis (10-12) and ventral rostrum
12 2 Lateral contact oflateral dome and ventral rostrum
13 3 Intersection ofaparallel to the axis (12-14) and lateral dome
14 2 Lateralmostpoint oflateral dome
15 3 Intersection ofaparallel to the axis (14-18) and lateral dome
16 2 Medialmost point oflateral dome
17 2 Maximum swelling ofdorsal dome
18 2 Dorsalmostpointoflateral dome
Figure 1
A. Statolith morphology. B. Localization of homologous points used. C. Definitions and respective types (sensu
Bookstein, 1991) ofthe 18 homologous points used.
tively wider (Figure 2). The tree constructed from the SMALL (smallerthan 120mmMLinL. vulgaris, smaller
distance matrix (Appendix 1) is arranged from the small- than 130 mm ML in S. officinalis) versus LARGE.
est to the largest individuals (Figure 3). Thus the feeble The statoliths ofother species analyzed under identical
morphological modification during growth is indeed a di- conditions (Sepia elegans, S. orbignyana, Alloteuthis me-
rected one. The same obtains in Sepia officinalis. In our dia) do not reveal growth-related morphological modifi-
sample, there isprogressive shortening oftherostrumand cations. Rossia macrosoma, Sepietta rieglecta, S. oweni-
widening of the attachment area (Appendix 2, Figure 4). ana, Sepiola sp., Abralia veranyi, Todaropsis eblanae,
Thus for the interspecific analysis Loligo vulgaris and Illex coindetii are not represented by sufficiently different
Sepia officinalis are represented by two categories each: ranges of sizes to allow an ontogenetic analysis. Never-
Page 268 The Veliger, Vol. 43, No. 3
^
235
Size classes (mm) O
198
#[42<ML<81] -0182
-0137
0[82<ML<119]
—
141\ 9160
'
O[120<ML<157]
—0158
e[158<ML<196]
M:^'105
0[197<ML<235] 155
-0189
Original species 12\
-0185
-O205
Target species J"—0195
r^
0125
146
0165
—
B
Loligo vulgaris > Loligo vulgaris '-0143
(ML= 42mm) (ML= 235 mm) -•69
0179
-0192
-(D113
169
-®117
©86
'
<D86
^
147
44
46
158
Ia2 = 2.37 i54
'52
42
52
Original species Targetspecies
Figure 3
Figure 2
Phenetic tree forLoligo vulgaris showing the hierarchy ofstato-
An example ofcomparison using LSTRA (comparison between lith morphologies as a function ofmantle length (ML).
two individuals of Loligo vulgaris of different sizes). A. Vector
field resulting from Procrustes adjustment. B. Presentation used
able in statolith morphology; males and females never
in this analysis.
clustered separately in the phenograms.
Variation between Species
theless, for Illex coindetii, recent data from a very wide
range of sizes reveal an ontogenetic change of statolith Pairwise analyses among loliginids (Alloteuthis media
shape (Gonzalez & Guerra, 1997). Our present data cor- and Loligo vulgaris) show that statoliths of Alloteuthis
respond to stage 2 described by these authors. media of any size resemble more closely the SMALL
Even when sexes were distinguishable in sufficiently Loligo vulgaris than the LARGE ones (Figure 5A, B).
large numbers of individuals (Sepia elegans, S. orbigny- Differences are rather modest (max. 2A- = 1.58, Appen-
ana, Illex coindetti), no sexual dimorphism was detect- dix 3) and are expressed mainly by the overall form of
J.-L. Dommergues et al., 2000 Page 269
A B
Sepia officinalis -> Sepia officinalis
(ML =48 mm) (ML= 191 mm) 170
0
191
-O 144
Size classes (mm)
• ML
[48 < < 83]
[84<ML<
119]
O [120<ML<
155]
Ia2= 1.37 O [156<ML< 191]
Figure 4
A. Comparison between two individuals ofSepia officinalis of different mantle lengths. B. Phenetic tree forSepia
ojficinalis showing the hierarchy of statolith morphologies as a function of mantle length (ML).
the statolith, which is more slender in AUoteuthis media tances are larger (max. SA- = 2.49, Appendix 3). Their
and in SMALL Loligo vulgaris, and by the lateral and statoliths are characterized by the lack of a ventral ros-
ventral expansion of the lateral dome, which is very trum (which implies superposition of points 5, 9, 10, 11;
marked in LARGE Loligo vulgaris. In contrast, the ven- Figure 5F), a strongly (especially dorsally) reduced at-
tral rostrum shows only very few morphological modifi- tachment area, and by a well-developed dorsal dome,
cations. This result suggests an ontogenetic heterochrony: which is only poorly demarcated from the lateral dome,
AUoteuthis media having paedomorphic statoliths com- however. The overall outline is slender in the statoliths
pared to Loligo vulgaris. of the Sepiolinae.
The morphological differences between oegopsid The analyses reveal particularly marked differences be-
squids (Abralia veranyi, Illex coindetti, Todaropsis eb- tween Sepiidae and Sepiolinae (max. SA- = 5.05, Ap-
lanae) are undeniable (max. 2A- = 3.38, Appendix 3), pendix 3). An intermediary position between these two
but they do not affect the general pattern ofstatolith mor- sets is heldby the sepiolidRossiamacrosoma (Figure 5G,
phology (Figure 5C): the ventral rostrum is short, the at- H), which appears closer to the sepiids (max. 2A- = 3.02,
tachment area is long comparedto the rest ofthe statolith, Appendix 3) than to the Sepiolinae (max. 2A- = 4.43,
the overall form is slender, and the lateral dome is rather Appendix 3). Apart from the lack of a (typically sepiid)
indistinct. subspherical lateral dome, the main difference between
A comparisonbetweenthe two teuthoidgroups (Myop- Rossia macrosoma and sepiid statoliths is the smallerros-
sida versus Oegopsida) reveals notable differences (for trum with a more rounded end and a wider lateral dome.
example a 2A- of 3.73 between LARGE Loligo vulgaris Moreover, the pairwise analyses performed between
and Illex coindetii: Figure 5D, Appendix 3). In compar- Sepia elegans and Rossia macrosoma, on the one hand
ison with L. vulgaris, I. coindetii has statoliths in which (see Figure 5G), and between Loligo vulgaris and Rossia
the rostrum is markedly reduced, the lateral dome trun- macrosoma, on the other (Figure 51), highlight the inter-
cated laterally, but well developed dorsally and ventrally, mediary position ofR. macrosoma between the Sepiidae
and which has a longer attachment area. and myopsid Teuthoidea. In contrast, the Sepiolinae ap-
The three species of Sepia Linnaeus, 1758, have very pear closer to the oegopsid Teuthoidea, as shown by the
similar statoliths (max. SA^ = 1.53, Appendix 3), always comparison between Illex coindetii and Sepietta oweni-
with a lateral dome forming a very distinct subspherical ana (Figure 5J).
structure (which sets them apart from all the other taxa
studied), a long and broad rostrum showing a truncated DISCUSSION
or broadly rounded end, and a large, massive attachment
area (Figure 5E). The Sepiolinae form anothergroup with The phenetic tree derived from the distance matrix (Ap-
high morphological coherence, although interspecies dis- pendix 3) gives a quantitative representation of relations
> >> > > > > > >
Page 270 The Veliger, Vol. 43, No. 3
— — —
Loligovulgaris(Small) Loligo vulgaris(Large) Illexcoindetii
. ^ , AUoteuthismedia ^ AUoteuthismedia Todaropsiseblanae
XA2= 1.15 ZA2-1.58 IA2= 1.74
— — —
Loligovulgaris(Large) Sepiaelegans Sepiettaoweniana
i-N Illexcoindetii r" Sepiaofficinalis(Large) Sepiettaneglecta
IA2 = 3.73 IA2=1.36 SA2=1.31
— — —
Sepia elegans Rossiamacrosoma Loligo vulgaris(Large)
Rossiamacrosoma Sepiettaoweniana Rossiamacrosoma
I
2:A2=2.28 SA2= 3.87 IA2= 2.39
J.-L. Dommergues et al., 2000 Page 271
between statolith morphologies in the species studied (Boletzky, 1995). Theresulting systematic changes within
(Figure 6). It reflects many of the taxonomic divisions the former Sepioidea, or within the Decabrachia as a
traditionally accepted (Voss, 1977; Mangold & Portmann, whole, are now highlighted by the possible transfer of
1989; Sweeney et al., 1992). Idiosepius to the Oegopsida based on nucleotide and ami-
For the Teuthoidea, the phenetic tree topology obtained no acid sequences processed with the Neighbour Joining
with our method suggests a clear separation ofMyopsida method, Bonnaud et al. (1997).
(with loliginid genera Loligo Lamarck, 1798, and AUo- Provided that this new position ofIdiosepius is not due
teuthis, Wiilker, 1920) and Oegopsida (represented by to an artefact of data processing (especially relating to
two families, the Enoploteuthidae with Abralia Gray, use of a distance method), the similarity of the statoliths
1849, and the Ommastrephidae with lUex Steenstrup, of Idiosepius (Jackson, 1988) with those of Sepiolinae
1880, and Todaropsis Girard, 1890). In contrast, the Se- suddenly appears in new light. Indeed these statoliths are
pioidea do not cluster Sepia and Rossia macrosoma, on similar not only to those of Sepiolinae, but also to those
the one hand, differ from the Sepiolinae (Sepiola Leach, of ommastrephid and enoploteuthid squids. Of course,
1817, Sepietta Naef, 1912), on the other Thus the stato- this observation should not be taken to mean that the
liths of the Sepiolidae fall under two distinct morpholo- Sepiolinae or the whole family Sepiolidae would now
gies, which correspond to the Rossiinae and Sepiolinae, have to follow in the wake of Idiosepius in view of the
respectively. other similarities (cf. Fioroni, 1981; Clarke, 1988).
Clarke & Maddock (1988b:182) concluded that stato- In contrast to the new position ofIdiosepius suggested
liths largely confirm a broad pattern as expected from by the above-mentioned molecular study, phylogenetic
general systematic studies. However, for the Sepiolidae, relationships of the Sepiolidae change depending on
they note that Heteroteuthis and Rossia are closer to the which subfamilies are included in the analysis: when rep-
Sepiidae than is Sepiola. resented by Sepietta and Heteroteuthis the Sepiolidae
The morphological similarity between the statoliths of cluster with the Sepiidae (Bonnaud et al., 1997), when
Rossia macrosoma and Sepia could be related to similar- represented by Rossia Owen, 1834, and Sepiola, they
ities in both animal and statolith sizes between Sepia and cluster with agroup containing ommastrephids along with
Rossia macrosoma, but the adult size of Heteroteuthis loliginids and sepiids, the latter two forming terminal sis-
Gray, 1849, is closer to that of Sepiola or Sepietta. This ter groups (Boucher-Rodoni & Bonnaud, 1996).
has to be kept in mind in attempts to interpret the dis- An interesting parallel appears in the distribution of
parity between the statolith morphologies of Rossiinae morphological characters in decabrachian spermatozoa.
and Sepiolinae in relation to functional constraints. Like- Healy (1989, 1990) observed that the respective forms in
wise, the morphological similarity between statoliths of the cuttlefish Sepia, in the loliginids Loligo and Alloteu-
Sepiolinae and of oegopsid squids could be related to this, and in the sepiolids Rossia and Sepietta are similar
similarities in statolith size, but it cannot be related to the for the differentiation of a mitochondrial spur at the fla-
adult sizes ofthe animals, which are very different. Thus gellar basis. In contrast, the acrosome comes in two
the question arises whether this similarity of statolith forms, one (rounded) showing greater similarity between
morphology might reflect a close phylogenetic relation- sepiid cuttlefish and loliginid squids, the other (elongate)
ship. This has to be discussed in relation to other pub- showing greatersimilaritybetweendifferent sepiolids (in-
lished data, and especially with a close look at Idiosepius cludingHeteroteuthis). However, the spermatozoaoiHet-
Steenstrup, 1881. eroteuthis are different from those ofRossia andSepietta;
Various data now call for a redefinition (or abandon- they have a periflagellar mitochondrial sleeve instead of
ment) ofthe higher taxa Sepioidea and Teuthoidea. With- a mitochondrial spur. Surprisingly, this mitochondrial
in the Teuthoidea, the suggested transfer ofChtenopteryx sleeve is very similar to what exists in Spirula Lamarck,
Appellof, 1890, from the Oegopsida to the Myopsida (to 1799, whereas the (elongate) acrosomes of spirulid sper-
join the loliginds, as suggested by Young, 1991, and matozoa are in their turn similar to those of the sepiolid
Brierley et al., 1996), is a minor change, but it may fore- spermatozoain general. But othermorphological and mo-
shadow greater rearrangements. The removal from the lecular data do not suggest Spirula to be the closest rel-
Sepioidea, either of the Sepiolidae together with the Se- ative of sepiolids.
piadariidae and the Idiosepiidae (Fioroni, 1981), or ofthe In both instances, statolith morphology and spermato-
Sepiolidae with the Idiosepiidae only (Clarke, 1988), has zoan morphology, one has to cope with a mosaic of fea-
already launched a reassessment of sepiolid relationships tures. This situation necessitates acarefulreassessment of
Figure 5
Some examples of pairwise comparisons selected to illustrate the morphological differences within studied Deca-
brachia.
Page 272 The Veliger, Vol. 43, No. 3
Sepia elegans
<p
Sepia officinalis (Small)
o Sepia officinalis (Large)
Sepia orbignyana
"° Rossia macrosoma
<> Loligo vulgaris (Large)
<' Loligo vulgaris (Small)
•^ Alioteuthis media
o
Abralia veranyi
Sepioidea
Sepiidae ^^ o
lllexcoindetii
Sepiolidae
(Rossiinae) *P
^ o Todaropsis
(Sepiolinae)
eblanae
Teuthoidea
(Myopsida) yv
Loliginidae \/
(Oegopsida) Sepietta neglecta \\
Enoploteuthidae
Ommastrephidae| _|_. ^ Sepiettaoweniana
\)^
(Illicinae) IZJ
o Sepiola sp
Figure 6
Phenetic tree constructed from the quantification of differences and similarities in the statoliths of 12 analyzed
species. All statoliths are drawn to the same scale. Note the overall size decrease from the top to the bottom ofthe
figure.
J.-L. Dommergues et al., 2000 Page 273
each of the characters considered. As to statolith mor- crostructure of the gladius and statolith from the boreal Pa-
phology, the subglobular shape of the lateral wing in Se- cific giant squid Moroteiithis rohusta (Oegopsida; Onycho-
teuthidae). Journal ofZoology, London 241:475-492.
pia then appears as a truly distinctive feature (a likely
synapomorphy) that is much more significant as a phy- BoLE(TMZoKlYl,usSc.a:v.C1e9p9h5a.loTphoedas)y.stePmpa.tic99p-o1si0t4ioninofS.thev.SeBpoiloeltizdkaye
logenetic signature than the overall structure ofthe stato- (ed.), Mediterranean Sepiolidae. Bulletin de I'lnstitut ocen-
lith. For the rest, it is the lack ofsuch distinctive features ographique de Monaco, Numero special 16.
that leads to an ostensible mixture of systematic groups, BoNNAUD, L., R. BoucHER-RoDONi & M. MoNNEROT. 1996. Re-
similarity ofform being inversely related to statolith size lationship of some coleoid cephalopods established by 3'
(Figure 6). More data from the subfamily Rossiinae, es- end of the 16S rDNA and cytochrome oxidase 111 gene se-
pecially from the small juvenile statoliths, are needed to quence comparison. American Malacological Bulletin 12(1/
2):87-90.
see whether the statoliths ofthe Sepiolinae represent pae- BoNNAUD, L., R. BouCHER-RoDONi & M. MoNNEROT. 1997. Phy-
domorphic forms derived from an ancestral situationclos- logeny ofcephalopods inferredfrom mitochondrial DNAse-
er to that of Rossia, or whether the latter results from quences. Molecular Phylogeny and Evolution 7(l):44-54.
hypermorphosis sensu Gould (1977). Complementary BooKSTEiN, F L. 1991. Morphometric Tools forLandmark Data.
sets of ontogenetic data from the Heteroteuthinae might Geometry and Biology. Cambridge University Press: Cam-
also be instructive. bridge. 435 pp.
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Only in Rossia, some emphasis on the horizontal channel Brierley, a. S., M. R. Clarke & J. P Thorpe. 1996. Ctenop-
teryx sicida. a bathypelagic loliginid squid? American Mal-
occurs (supposedly related to turning in the yawing
plane). Discriminant analysis separates these statocysts BuDEaLcMoAloNgNi,calB.BuUl.l,etRi.nS1c2H(i1P/P2):&13S7.-v1.43B.oLETZKY. 1997. Cepha-
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might reflect the emphasis on the horizontal channel and the United Kingdom 58:701-712. —
Clarke, M. R. 1988. Evolution of recent cephalopods a brief
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