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Stranded shell of Spirula spirula from the Canary Islands (coll. Kerstin Warnke, Freie Universität Berlin, branch palaeontology). The arrows indicate the locations of chamber and septum. The protoconch is slightly damaged; scale bar = 5 mm.
Source publication
The mesopelagic recent cephalopod Spirula Lamarck,
1799 seems to be a suitable model organism for
approaching the embryonic development of the extinct
ammonoids. As no spawned egg masses of Spirula were
found, artificial fertilization provides an opportunity to
obtain information about the embryonic development.
The critical point is the correct re...
Contexts in source publication
Context 1
... resin for fixation during extraction of septa. The resin is of such high viscosity that intrusion of the substance into the chambers of the shell is avoided. No material that had been contaminated with resin was selected for analysis. A blast stylus W 224 (Krantz) was used to remove the outer shell and extract material from individual septa (Fig. 2). From specimens A, B and C a full set of septa was sampled, from D and E only septum 1-11. The carbonate was collected in TabTop Microcentrifuge tubes 1.5 ml (Roth, Karlsruhe-Germany) and sent to the Leibniz laboratories at Christian-Albrechts- Universität in Kiel for analysis. Measurement of oxygen and carbon isotope ratios was ...
Context 2
... as for all other septa. All samples are chosen with attention to a full set of septal layers as temporal inconsistencies during precipitation of single layers were reported from Nautilus septa ( Oba et al. 1992). A total of 11 randomly chosen samples from the outer shell wall of the preceding chamber was analysed to compare internal variations (Fig. 2). These isotope ratio measurements were run at the Freie Universität Berlin on a Thermo Electron Mat-253 isotope ratio mass spectrometer (IRMS) and Gasbench II carbonate device (e.g. Spöttl & Vennemann 2003). For isotope analysis about 200 μg carbonate was loaded into Exetainers and reacted with 100% H 3 PO 4 at 70°C. All isotope data ...
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In sections of the Rhenish Massif, the early Namurian El goniatite interval (= Zone of Tumulites pseudobilinguis) can be subdivided into seven goniatite zones on the basis of girtyoceratid ammonoids. These are from bottom to top Edmooroceras pseudocoronula Zone, Edmooroceras medusa Zone, Sundernites horni Zone, Tumulites angustus Zone, Tumulites ps...
Citations
... If individuals of T. minimus changed their habitat during their life cycle and became fossilised in their respective habitats, this would result in bias in the proportion of variously aged specimens. Ontogenetic active migration is assumed among some Mesozoic ammonoids and well known in many modern cephalopods (ammonoids; Morton 1988;Lukeneder et al. 2010;Ikeda and Wani 2012;Brayard and Escarguel 2013;Lukeneder 2015;Moriya 2015;modern cephalopods: Clarke 1970;Crick 1988;Landman 1988;Oba et al. 1992;Westermann 1996;Rexfort and Mutterlose 2006;Lukeneder et al. 2008;Price et al. 2009;Warnke et al. 2010;Dunstan et al. 2011b;Ritterbush et al. 2014). ...
Mature modifications, ontogeny, and dimorphism of the small-sized tetragonitid ammonoid Tetragonites minimus
were investigated in 43 specimens from the Santonian, Upper Cretaceous of the northwestern area of Hokkaido, Japan.
Four types of mature modifications were recognised in the shell diameters of 11–13 mm and 16–19 mm, and two
differently sized adults were regarded as microconchs and macroconchs respectively. The conch forms of dimorphic
pairs were similar in juvenile but differ in the later stage. The supplementary analysis showed that the remarkable
adult size differences in antidimorphs continued at least in the Turonian–Santonian. The mature size and size differ�ence between dimorphic pairs decreased chronologically. 36 specimens (84% of examined specimens) were mature,
and immature shells were rare in the Santonian. Most of the shells were remarkably well preserved, indicating that
T. minimus assemblage fossilised quickly near their original habitat without long-distance post-mortem transport.
Hence the bias in the fossil occurrence of adult T. minimus is unlikely to be due to taphonomy such as the bias of
fossilisation potential and floatability in the bottom currents. Tetragonites minimus might have been changing their
habitats during their life cycle.
... Lukeneder et al. (2008) calculated temperatures between 6 • C and 12 • C and considered S. spirula to hatch at a depth of more than 1000 m. This also agrees with stable oxygen isotope data from live-caught S. spirula from the Canary Islands indicating a variation of habitat depth during ontogeny between 350 and 800 m (Warnke, Oppelt & Hoffmann, 2010). ...
Belemnites are an extinct group of Mesozoic coleoid cephalopods with a fossil record ranging from the early Late Triassic [about 240 million years ago (Mya)] to the Cretaceous/Palaeogene boundary (65 Mya). Belemnites were widely distributed, highly abundant and diverse, and an important component of Mesozoic marine food webs. Their internal shells, specifically their low‐Mg calcite rostra, have been used as palaeoenvironmental carbonate archives for the last 70 years. This is primarily due to the assumption that the rostrum calcite formed in equilibrium with the oxygen isotope composition of ambient sea water. Of prime importance for the reliable interpretation of isotope data derived from these biogenic carbonates is a robust reconstruction of the palaeobiology of their producers. Here we provide a critical assessment of published reconstructions of belemnite soft‐body organization and their lifestyle and habitats. Different lines of evidence, including sedimentological, geochemical, morphological, and biomechanical data, point towards an outer shelf habitat of belemnites, for some taxa also including the littoral area. Belemnite habitat temperatures, oxygen content, salinities, and life span are constrained based on observations of the ecology and life history of modern coleoids. Belemnite habitat depth might have been largely controlled by food and temperature, with a temperature optimum between 10°C and 30°C. The distribution of modern coleoids is for most species restricted to well‐oxygenated water masses and a salinity between 27 and 37 psu. The trophic position of belemnites as both predators and prey is documented by unique fossil finds of stomach contents and soft tissue preservation, such as jaws, hooks, and ink sacs. Belemnites were medium‐sized predators in the epipelagic zone (not deeper than ∼200 m) hunting for crustaceans, other cephalopods, and fishes. Taxa with elongated rostra probably were fast and highly manoeuvrable swimmers. Forms with conical rostra represent slow but highly manoeuvrable swimmers, and forms with depressed rostra likely had a bottom‐related life habit. Predators of adult belemnites were sharks, bony fishes, and marine reptiles. Belemnites, like most of the modern coleoids, were relatively short lived, most likely living only for 1–2 years. Understanding the biomineralization of belemnite rostra is highly relevant for an improved interpretation of their geochemistry. Here we confirm that belemnite rostra are composed of low Mg‐calcite fibres, but they do not contain distinct types of laminae. These fibres are composed of two distinct calcite phases. One phase is a filigree network of tetrahedral organic‐rich calcite and the second phase is represented by organic‐poor calcite.
... Spirula spirula ( Fig. 2A,B) is one of the few exceptions, where the ramshorn-shaped shell does not occupy the full ML. Isotopic signatures in the shells that possess the IC (Lukeneder et al. 2008;Warnke et al. 2010) suggest that hatchlings emerge from the egg with the shell containing two to three chambers (IC = 0.6-0.7 mm), which agrees well with captures of the youngest specimens with 2-3 mm ML and a two-chambered shell (Chun 1914;Bruun 1943;Clarke 1970). Similarly, Yamaguchi et al. (2015) correlated lower rotational angles between septa 1 and 3 with hatching. ...
Coleoid cephalopods exhibited two distinct reproductive strategies, resulting in small pelagic and large demersal hatchlings, both in the geologic past and recently. In ectocochleate cephalopods, the hatching event is recorded in shell structures (e.g., nepionic constrictions, ultrastructural shifts, or ornamentation differences). In contrast, well-defined hatching markers do not exist on coleoid shells. Changes in septal spacing may be evidence of hatching (e.g., some extant sepiids), but not in all fossil groups. In the present study, we subdivide the early ontogenetic shells of phragmocone-bearing coleoids (belemnoids, spirulids, and sepiids) into key architectural stages and describe their reference to the hatching event. Belemnoids exhibit three key stages, the second of which is here considered to occur shortly before or after hatching. In spirulids and sepiids, there is only one key stage. In Mesozoic belemnoids, spirulids, and sepiids, hatching accordingly occurred with a total shell length of less than 2 mm, which corresponds to mantle lengths of small planktonic hatchlings. Production of small pelagic hatchlings and thus small eggs was therefore the dominant reproductive strategy within the Coleoidea. The first evidence of enlarged hatchlings appeared during the Maastrichtian in Groenlandibelus. During the Eocene, the large-egg strategy apparently became more widespread, particularly in belosaepiids.
... Spirula is well known for its daily vertical migrations, spending the daytime around depths of about 600-700 m and the night around depths of 100-300 m (Clarke, 1969). Because live caught specimens are rare, recent attempts used the δ 18 O signal of their aragonitic shell to decipher, e.g, vertical ontogenetic migration patterns (Lukeneder et al., 2008;Price et al., 2009;Warnke et al., 2010). Vertical migration can be achieved by using the jet as well as the two fins while predominantly hanging head-down in the water column (Hoffmann and Warnke, 2014). ...
Here, we report on different types of shell pathologies of the enigmatic deep-sea (mesopelagic) cephalopod Spirula spirula. For the first time, we apply non-invasive imaging methods to: document trauma-induced changes in shell shapes, reconstruct the different causes and effects of these pathologies, unravel the etiology, and attempt to quantify the efficiency of the buoyancy apparatus. We have analysed 2D and 3D shell parameters from eleven shells collected as beach findings from the Canary Islands (Gran Canaria and Fuerteventura), West-Australia, and the Maldives. All shells were scanned with a nanotom-m computer tomograph. Seven shells were likely injured by predator attacks: fishes, cephalopods or crustaceans, one specimen was infested by an endoparasite (potentially Digenea) and one shell shows signs of inflammation and one shell shows large fluctuations of chamber volumes without any signs of pathology. These fluctuations are potential indicators of a stressed environment. Pathological shells represent the most deviant morphologies of a single species and can therefore be regarded as morphological end-members. The changes in the shell volume / chamber volume ratio were assessed in order to evaluate the functional tolerance of the buoyancy apparatus showing that these had little effect. Key words: pathology; parasitism; Spirula; mesopelagic; ecology; predator; buoyancy; cephalopods
... All of the carbonate skeleton forming groups have by now been analyzed for these proxies. This includes several works about the composition of the shells of nautilids (Eichler & Ristedt, 1966;Cochran et al., 1981;Taylor & Ward, 1983;Oba et al., 1992;Landman et al., 1994; as well as the calcite from their jaws (Kruta et al., 2014), the aragonitic endoskeletons of Spirula spirula (Lukeneder et al., 2008;Warnke et al., 2010) and sepiids Dance et al., 2014), and the calcitic shells of the pelagic octopus Argonauta argo . ...
... Several studies have documented that the oxygen stable isotope ratio (δ 18 O) of aragonitic exoand endoskeletons of extant cephalopods is useful to reconstruct the living conditions of these animals (e.g., Landman et al., 1994;Lukeneder et al., 2008;Warnke et al., 2010;Dance et al., 2014). The extent to which biogeochemical data in argonaut shells reflect environmental parameters, however, is yet unknown. ...
The Coleoidea are by abundance as well as diversity the dominant group of cephalopods in modern seas and an important component of marine ecosystems. They are characterized by an endoskeleton which is largely reduced in many recent taxa. This endoskeleton can be covered by secondary carbonate deposits forming a so-called rostrum. The rostra of the extinct belemnites represent the most common coleoid fossils of the Jurassic and Cretaceous. Due to their low-Mg calcite composition, which is relatively stable during diagensis, belemnite rostra have become one of the most frequently used geochemical archives for the marine paleoenvironment. Paleoenvironmental proxies commonly derived from the rostrum calcite are stable carbon and oxygen ratios (δ13C, δ18O), as well as the element ratios Mg/Ca and Sr/Ca. These proxy data have been predominantly applied to reconstruct paleotemperature and carbon cycle trends.
Despite this widespread application, there are several factors which restrict the use of belemnite rostra as paleoenvironmental archives. The primary microstructure of belemnite rostra is controversially debated, with reconstructions ranging from originally aragonitic, highly porous low- Mg calcitic, to mostly dense low-Mg calcitic. Many structural features of the rostra have not been investigated in detail in a comparative paleontological framework. The likely nektic, active lifestyle of belemnites makes interpretation of their geochemical data more complicated than that of benthic animals due to possible migration. Potential vital effects, formation of the rostrum calcite out of (isotope)chemical equilibrium due to biomineralization processes, are often neglected. Furthermore, all fossils are subject to different extents of diagenesis which might alter their geochemical composition. Screening for diagenetic alteration is difficult in belemnites, because no recent cephalopod provides a structure which is identical to the calcitic rostrum and could be used as a benchmark of perfect preservation.
This thesis consists of four studies which investigate different aspects of the structure and geochemistry of recent (argonauts; Argonauta argo) and fossil (belemnites; Belemnitida) calcitic skeletons of coleoid cephalopods. The first study deals with belemnite rostra of the Nusplingen Plattenkalk (Upper Jurassic, southwestern Germany). Oxygen stable isotope values of the rostra provide paleotemperatures inconsistent with their depositional setting. The predominant influence on their geochemical record was probably a locally or regionally increased evaporation rate. These findings highlight the importance of a critical interpretation of belemnite data in a sedimentological/paleontological framework.
III
The second study is the first to investigate geochemical data of the calcitic shells of the pelagic argonauts. High-resolution sampling of the shells reveals a complex combination of vital effects related to growth rate, as well as environmental influences acting on the shells’ δ18O, δ13C, Mg/Ca, Sr/Ca, and Ba/Ca ratios. Environmental influences are, nevertheless, only revealed if they are constrained by the potential drift/migration path and habitat of these cephalopods.
The third study presents microstructural and geochemical data derived from the belemnite Neohibolites minimus. The two growth stages of their rostra have distinct microstructures and geochemical compositions. These microstructures and cathodoluminescence patterns of the rostra are compared to those of argonaut shells. Development and evolution of the rostra is discussed and evidence for vital effects in these belemnites presented.
Finally, the fourth study compares two distinct belemnite taxa (Mesohibolites sp., Duvalia grasiana) which experienced the same diagenetic pathway. Differences in preservation of these taxa are reflected in their geochemistry and cathodoluminescence patterns. Diagenesis of the rostra was controlled by their different primary microstructure. The largely porous pseudoalveoli of Mesohibolites were cemented during diagenesis while large sections of the D. grasiana rostra recrystallized due to their high primary organic content. This results in an invariable loss of large sections of the ontogenetic geochemical record of the rostra and necessitates a precise taxonomic identification of the rostra.
In conclusion, these studies reveal that I) the exact environmental parameters which influence the skeletal geochemistry are often difficult to discern in recent and particularly in fossil coleoid cephalopods, II) vital effects might influence the geochemical data significantly, distorting environmental signals, and III) diagenesis of belemnite rostra is influenced by differential reaction of their microstructures, often leading to the loss of ontogenetic records and necessitating a precise taxonomical determination of analyzed rostra. All of these factors largely restrict the utility of belemnite rostra as environmental archives.
... Because the environment in the oceans and seas still is inadequately known, it is often difficult to understand the function of the vertical migration. Also, Spirula is a diurnal vertical migrant (Bruun 1943;Clarke 1969Clarke , 1970Warnke et al. 2010;Hoffmann & Warnke 2014). According to Clarke (1969) the entire population lives during daylight at water depths of 600-700 m, but ascends at night to the depths of 100-300 m. ...
... According to Clarke (1969) the entire population lives during daylight at water depths of 600-700 m, but ascends at night to the depths of 100-300 m. Studies of stable isotopes in the shell septa during the ontogeny (Warnke et al. 2010) show that the hatching depth of Spirula is about 800 m. The young animal stays at this depth about 10-14 weeks and migrates then upwards to an average depth of 350-400 m where it stays the following half year, then descending to an average depth of 550-600 m. ...
The shell wall in Spirula is composed of prismatic layers, whereas the septa consist of lamello-fibrillar nacre. The septal neck is holochoanitic and consists of two calcareous layers: the outer lamello-fibrillar nacreous layer that continues from the septum, and the inner pillar layer that covers the inner surface of the septal neck. The pillar layer probably is a structurally modified simple prisma layer that covers the inner surface of the septal neck in Nautilus. The pillars have a complicated crystalline structure and contain high amount of chitinous substance. The interspaces between the pillars probably are traversed horizontally by numerous chitinous membranes like in the cuttlebone chambers in Sepia. The connecting ring is composed of similar two layers as that in the extant Nautilus: the outer spherulitic?prismatic layer and the inner chitinous layer. The spherulitic?prismatic layer takes its origin on the outer surface of the septal neck, whereas the inner chitinous layer is the non-calcified continuation of the lamello-fibrillar nacreous layer of the septal neck. The siphuncular structure in Spirula is compared with that in the extant Nautilus, fossil nautilosiphonate nautiloids, and five taxa of coleoids.
... Wellpreserved shells provide a reliable geochemical archive that reflects the life span migration cycle. Lukeneder et al. (2008), Price et al. (2009) and Warnke et al. (2010) used the aragonitic internal shells (Mutvei 1964;Dauphin 1976Dauphin , 2001aWatabe 1988;Doguzhaeva 1996Doguzhaeva , 2000Doguzhaeva et al. 1999;Mutvei and Donovan 2006) as a geochemical proxy to interpret the ontogenetically related habitat changes. Subsequently, an ontogenetically controlled vertical migration was concluded. ...
... After hatching in deep, cold seawater below 1000 m at temperatures around 4-6°C, they start as a deep-water dweller during early ontogenetic stages but switch to warmer mid-water habitats (at 12-14°C) during growth (Lukeneder et al. 2008; see Price et al. 2009, andWarnke et al. 2010). Finally, fully grown adults tend to retreat once again to slightly deeper and cooler environments. ...
In September 2014, the 9th International Symposium Cephalopods—Present and Past (ISCPP) and the 5th International Coleoid Symposium were held at the University of Zurich. The numerous contributions from two joint symposia fill more than one special issue. After the first special issue, which was published in 2015 in the Swiss Journal of Palaeontology (Vol 134, Issue 2), the present second special issue also contains contributions from all fields of research on fossil and Recent cephalopod. In this editorial, we provide a short obituary honouring Fabrizio Cecca and report from the three conference field trips.
... Several studies have documented that the oxygen stable isotope ratio (δ 18 O) of aragonitic exo-and endoskeletons of extant cephalopods is useful to reconstruct the living conditions of these animals (e.g., Landman et al. 1994;Auclair et al. 2004;Rexfort and Mutterlose 2006;Lukeneder et al. 2008;Price et al. 2009;Warnke et al. 2010;Dance et al. 2014). The extent to which biogeochemical data in argonaut shells reflect environmental parameters, however, is yet unknown. ...
The argonauts (genus Argonauta) are enigmatic cephalopods. They have a cosmopolitan distribution in subtropical and tropical seas, where they inhabit the epipelagic zone. Their biology, ecology, and life cycle are poorly understood. It is for the first time that stable isotope (δ13C, δ18O) and element ratios (Mg/Ca, Sr/Ca, Ba/Ca) from three argonaut shells have been analyzed in order to test whether their life cycle and habitat are reflected in these data. The three studied shells have been collected in October 2012 from a mass stranding in Yoichi Bay, Hokkaido, Japan. The specimens were sampled along the keel of the shells to acquire ontogenetic records and along growth-sections of the shells to obtain synchronous data of differing shell growth rates. Carbon and oxygen isotope values as well as Mg/Ca ratios are in part controlled by the shell growth rate. Sr/Ca values show similar ontogenetic trends in the three shells. Comparison with measured sea surface temperature data indicates a temperature control on δ18O, Mg/Ca, and Sr/Ca, and a fast growth of the argonaut shell. Ba/Ca ratios of the shells might record environmental parameters. These new data highlight the influence of vital effects, but they also demonstrate that argonaut shell isotopic and elemental records can be used to understand the life cycle of these animals better.
... We also discuss the ability of ammonoids to use their phragmocone to obtain neutral buoyancy. A major line of reasoning is the actualistic comparison with living nautilids (e.g., Ward 1979Ward , 1982Ward , 1986 and other phragmoconebearing cephalopods (e.g., Ward and Boletzky 1984;Warnke et al. 2010). The upward acting buoyant force is a product of the volume and density of the displaced liquid (in this case seawater, since all cephalopods are marine) which is equivalent to the volume of the submerged object, its magnitude is equal to the weight of the displaced fluid (Archimedes principle, see, e.g., Heath 1897). ...
... Depth distribution during ontogeny is fortunately also recorded in the stable oxygen isotopes of these cephalopod shells. Based on the shells of two live caught specimens of Spirula, Warnke et al. (2010) documented ontogenetic changes in terms of depth distribution. Juveniles hatch at around 800 m water depth and subsequently migrate upwards to around 350-400 m; as adults, they sink again down to about 550-600 m (Warnke et al. 2010). ...
... Based on the shells of two live caught specimens of Spirula, Warnke et al. (2010) documented ontogenetic changes in terms of depth distribution. Juveniles hatch at around 800 m water depth and subsequently migrate upwards to around 350-400 m; as adults, they sink again down to about 550-600 m (Warnke et al. 2010). ...
The buoyancy of ammonoids is one of the most controversial issues of ammonoid paleobiology. This chapter gives a short historical review about attempts made to clarify the potential function of the cephalopod chambered shell (phragmocone) and ammonoid life habits either as benthic crawler or as free swimmers in the water column. In order to understand efficiency of buoyancy control and the mode of life of the extinct ammonoids decoupling of cameral liquid, process of osmotic pumping including local osmosis, pre-septal gas, and the role of the siphuncle and cameral liquid were discussed extensively. It is accepted that processes like osmotic pumping and local osmosis act in ammonoids due to similar architecture of the extant relatives including the presence of a siphuncle. Additionally, the calculation of buoyancy represents a major task which depends on exact reconstructions of volumes and densities for shell and soft body. With the rise of 3D-imaging techniques the determination of volumes were enhanced and now represent an important step towards more precise buoyancy calculations.
... Wellpreserved shells provide a reliable geochemical archive that reflects the life span migration cycle. Lukeneder et al. (2008), Price et al. (2009) and Warnke et al. (2010) used the aragonitic internal shells (Mutvei 1964;Dauphin 1976Dauphin , 2001aWatabe 1988;Doguzhaeva 1996Doguzhaeva , 2000Doguzhaeva et al. 1999;Mutvei and Donovan 2006) as a geochemical proxy to interpret the ontogenetically related habitat changes. Subsequently, an ontogenetically controlled vertical migration was concluded. ...
... After hatching in deep, cold seawater below 1000 m at temperatures around 4-6°C, they start as a deep-water dweller during early ontogenetic stages but switch to warmer mid-water habitats (at 12-14°C) during growth (Lukeneder et al. 2008; see Price et al. 2009, andWarnke et al. 2010). Finally, fully grown adults tend to retreat once again to slightly deeper and cooler environments. ...
... Note, however, that ocean surface temperatures are not the crucial parameters for the life of Spirula (Lukeneder et al. 2008; for oceanic temperatures see Mehra and Rivin 2010; GRTOFS 2015). As also shown by stable isotope studies (Lukeneder et al. 2008;Price et al. 2009, andWarnke et al. 2010) on S. spirula shells, the life cycle takes place within a water depth range from 1000 m up to 200 m (Bruun 1955;Clarke 1970;Reid 2005;Haimovici et al. 2007;Hoffmann and Warnke 2014). Reid (2005) and Warnke and Keupp (2005) concluded a distribution of S. spirula in subtropical and tropical oceanic waters where the water temperature is 10°C or warmer at a depth of 400 m (Lu 1998;Reid 2005), 800 m (Hoffmann and Warnke 2014) and 1000 m (Warnke and Keupp 2005; for oceanic temperatures see Mehra and Rivin 2010;GRTOFS 2015). ...
The ram’s horn squid Spirula spirula is a unique deep-water marine organism whose life cycle remains enigmatic. Interpretations of its ecology and habitat preferences are currently based solely on dredging, on fishery data, stable isotope data and rare molecular genetic analyses of dead specimens. These methods form the basis to decipher phylogeographic questions of otherwise unobservable deep-sea animals such as S. spirula. Here, new morphological data from internal shells (specimens n = 408, analysed n = 260) are presented from 12 different populations over huge distances, from the Atlantic, Indian and the Pacific Oceans. A monospecific status is assumed for Spirula, with its species S. spirula. The dataset shows a highly variable shell morphology including size distribution within distinct populations. Populations from the Indian Ocean are larger than those from the Atlantic and the Pacific. Specimens from the northern Indian Ocean (Maldives, Sri Lanka, Thailand) are larger than specimens from the eastern Indian Ocean (Mauritius, Tanzania) and the south-eastern Indian Ocean (western Australia). Specimens from the eastern Atlantic (Canary Islands) are smaller than those of the western Atlantic (Brazil, Tobago). The Canary Islands yielded by far the smallest specimens, while the largest specimen comes from Thailand. Specimens from the locality at eastern Australia (south-west Pacific) have an intermediate size range. Morphologic and geographic data suggest a geographically induced size differentiation within S. spirula. Preliminary findings on conchs mirror the known (from soft parts) existence of two sexual dimorphs in Spirula. The next step would be to collect more material from other localities. A more detailed morphometric approach based on specimens from which the sexes are known is required to enable a detection of the presence of sexual dimorphism by morphometric analyses on internal shells of Spirula.
