taxonID	type	description	language	source
03F74A577A62FFD0D25FFA79FBADFE2A.taxon	description	A. nouryi was described by Lorois in 1852. The identification of this species resides solely in features of the shell, which is described as elliptical with numerous fine lateral ribs and weak keel tubercles. Fig. 3 incorporates a 1 A third large form also washes up on southern Gulf of California beaches in spring and is regularly attributed to the species A. pacificus, a synonym of A. argo; see Finn (2013) for details. reproduction of the illustration presented by Lorois, 1852 (plate 1, figure 5), and illustrations of a shell from the Gulf of California that is consistent with the original description (shell # 109, SBMNH 345768). According to Keen (1971) “ the ‘ shell’ is more elliptical than that of A. cornutus, with only the early part of the coil moderately well tinged with brown along the wide and weak tuberculate keel. The surface is delicately ribbed and has a finely granular texture ” (p. 895). Voss (1971) believed that “ Argonauta nouryi is a distinctive species […]. The shells are longer than in any other species of Argonauta, the ribs are more numerous, there are no distinct tubercles marking the edges of the carinal area; the carina is wide, very convex, and covered by numerous, small, blunt tubercles formed by the crisscrossing of the ribs ” (p. 32).	en	Finn, Julian K. (2018): Recognising variability in the shells of argonauts (Cephalopoda: Argonautidae): the key to resolving the taxonomy of the family. Memoirs of Museum Victoria 77: 63-104, DOI: 10.24199/j.mmv.2018.77.05, URL: http://dx.doi.org/10.24199/j.mmv.2018.77.05
03F74A577A62FFD0D25FFA79FBADFE2A.taxon	description	A mixed lot As described in the Materials and Methods section above, the 157 shells in the collection at SBMNH were collected on the same beach in Baja California on the same day. These shells had previously been identified as representing both A. cornutus and A. nouryi and were registered accordingly: SBMNH 345766, Argonauta cornutus 93 shells; SBMNH 345768, Argonauta nouryi, 64 shells. Initial examination of the lots indicated that the shells had been attributed to either A. cornutus or A. nouryi based on the presence or absence of ears – a character historically attributed to only A. cornutus. Further examination of the lot revealed that separation of the shells into two distinct groups (i. e. either A. cornutus or A. nouryi) was not as straightforward as first thought. While some shells within the lot displayed all the characters associated with either A. cornutus or A. nouryi, the lot also appeared to contain shells with combinations of the attributes of the two shell types. To illustrate this variation, three shells of similar size but varied appearance were selected. Fig. 5 presents photographs of these three shells from multiple perspectives: • • • Shell # 74 (SBMNH 345766), cornutus-type voucher (fig. 5 a, i – iv and fig. 4 c). Shell morphometrics: ShL 65.0; ShW 4.0; ShB 40.7; RC 45; EW 58.1; ApL 45.9; ApW 28.4; KW 15.6; KTC 27. Shell # 42 (SBMNH 345766), intermediate voucher (fig. 5 b, i – iv). Shell morphometrics: ShL 61.2; ShW 3.1; ShB 36.4; RC 47; EW 36.1; ApL 43.1; ApW 30.9; KW 14.0; KTC 32. Shell # 109 (SBMNH 345768), nouryi-type voucher (fig. 5 c, i – iv and fig. 3 b). Shell morphometrics: ShL 66.5; ShW 2.4; ShB 39.9; RC 54; EW (28.3); ApL 48.8; ApW 32.5; KW 15.8; KTC 54. While it would be straightforward to attribute shell # 74 (fig. 5 a) to A. cornutus Conrad, 1854, and shell # 109 (fig. 5 c) to A. nouryi Lorois, 1852, placement of shell # 42 (fig. 5 b) presents problems. While shell # 42 possesses the aperture shape of A. cornutus, it lacks its protruding ears. While shell # 42 possesses the keel tuberculation and reduced ventral keel tubercles of A. nouryi, its dorsal keel tubercles are large and pronounced. To determine whether there was a significant difference between eared and earless shells within the lot, a quantitative approach was undertaken. All intact shells within the lot were individually measured and weighed. All shells were designated as being either eared or earless based on the relative EW and ApW measurements. Because EW is an external measurement (i. e. measured across the extremities of the opposing ears) and ApW is an internal measurement (i. e. measured between the lateral walls of the shell), 1.0 mm was added to the ApW to accommodate for the thickness of the lateral walls of the shell. Shells were classified as follows: • • eared = EW> ApW + 1.0 mm (103 shells) earless = EW ≤ Apw + 1.0 mm (35 shells). Scatter plots were generated to compare eared and earless shells for all measured characters. Characters of primary interest were those previously reported to distinguish A. cornutus and A. nouryi. Shell shape. The most universally recognised character of A. nouryi is reportedly the elliptical shape of the shell: “ The whorls increase in size very rapidly and the last is very elongate. Viewed laterally it is much shallower than is usual in the genus ” (Robson, 1932, p. 198). The shells are said to be “ more elliptical than that of A. cornutus ” (Keen, 1971, p. 895) and “ longer than in any other species of Argonauta ” (Voss, 1971 a, p. 33). To investigate variation in shell shape across the lot, ShB was plotted against ShL (fig. 6). Probability plots indicate that both ShB and ShL follow normal distributions. An ANCOVA was used to determine if the slopes of the linear regression lines, generated for eared and earless shells, were the same or different. Shell type (eared or earless) was the independent variable, ShB the dependent variable and ShL the covariate. The ANCOVA revealed that the slopes of the regression lines are not equal and hence a significant difference in shell shape exists between eared and earless shells (F (1, 136) = 5.58, p = 0.02). Rib count. Argonauta nouryi shells are reported to have more ribs than A. cornutus shells: the ribs in A. nouryi are “ more numerous ” than in other species of Argonauta, while A. cornutus is reported to have “ few radial ribs ” (Voss, 1971, p. 32 – 33). To investigate variation in the number of ribs per shell across the lot, RC was plotted against ShL (fig. 7). Probability plots indicate that both RC and ShL follow normal distributions. An ANCOVA was used to determine if the slopes of the linear regression lines, generated for eared and earless shells, were the same or different. Shell type (eared or earless) was the independent variable, RC the dependent variable and ShL the covariate. The ANCOVA revealed that the slopes of the regression lines are not equal and hence a significant difference in the number of ribs per shell does exist between eared and earless shells (F (1, 136) = 21.2, p <0.001). Other features. To investigate the full range of quantifiable shell characters across the lot, scatter plots were similarly generated to investigate KTC, ApL, ApW and KW. Keel tubercle count. To investigate variation in the number of keel tubercles per shell across the lot, KTC was plotted against ShL (fig. 8). Probability plots indicate that both KTC and ShL follow normal distributions. An ANCOVA was used to determine if the slopes of the linear regression lines, generated for eared and earless shells, were the same or different. Shell type (eared or earless) was the independent variable, KTC the dependent variable and ShL the covariate. The ANCOVA revealed that the slopes of the regression lines are not equal and hence a significant difference in the number of keel tubercles per shell does exist between eared and earless shells (F (1, 136) = 51.66, p <0.001). Aperture length. To investigate variation in the length of the shell apertures across the lot, ApL was plotted against ShL (fig. 9). Probability plots indicate that both ApL and ShL follow normal distributions. An ANCOVA was used to determine if the slopes of the linear regression lines, generated for eared and earless shells, were the same or different. Shell type (eared or earless) was the independent variable, ApL the dependent variable and ShL the covariate. The ANCOVA revealed that the slopes of the regression lines are not equal and hence a significant difference in the length of the aperture does exist between eared and earless shells (F (1, 136) = 18.63, p <0.001). Aperture width. To investigate variation in the width of the shell apertures across the lot, ApW was plotted against ShL (fig. 10). Probability plots indicate that both ApW and ShL follow normal distributions. An ANCOVA was used to determine if the slopes of the linear regression lines, generated for eared and earless shells, were the same or different. Shell type (eared or earless) was the independent variable, ApW the dependent variable and ShL the covariate. The ANCOVA revealed that the slopes of the regression lines are not equal and hence a significant difference in the width of the aperture does exist between eared and earless shells (F (1, 136) = 4.07, p = 0.046). Keel width. To investigate variation in the width of the shell keels across the lot, KW was plotted against ShL (fig. 11). Probability plots indicate that both KW and ShL follow normal distributions. An ANCOVA was used to determine if the slopes of the linear regression lines, generated for eared and earless shells, were the same or different. Shell type (eared or earless) was the independent variable, KW the dependent variable and ShL the covariate. The ANCOVA revealed that the slopes of the regression lines are equal and hence a significant difference in the width of the keel does not exist between eared and earless shells (F (1, 136) = 0.87, p = 0.353). Statistical analysis indicates that significance differences in shell dimensions was associated with the presence or absence of ears. Eared shells have significantly lower RC (p <0.001), lower KTC (p <0.001), shorter ApL (p <0.001), increased ShB (i. e. shortened; p = 0.02) and increased ApW (p = 0.046). Earless shells have significantly higher RC (p <0.001), higher KTC (p <0.001), longer ApL (p <0.001), reduced ShB (i. e. elongate; p = 0.02) and reduced ApW (p = 0.046). KW was found to not be significantly different between shell types (p = 0.353). Historically, the features of eared and earless shell types have been considered to represent separate species such that features of eared shells are considered characteristic of A. cornutus, while features of earless shells are considered characteristic of A. nouryi. Two types of shell formation Close examination of individual shells revealed that features considered characteristic of each shell type could occur on a single shell. While individual shells could display features of both eared and earless shell types, the characters did not appear in isolation. Sequential growth sections of the shells appeared to display all the characteristics of one shell type or another. For example, the initial component of the shell (the smallest whorl) may display all the characters historically associated with an A. cornutus shell while the latter component (the larger final whorl) may display all the features associated with an A. nouryi shell. The most dramatic examples were shells that appeared to have been repaired over the course of the argonaut’s life. Fig. 12 presents photographs of one such shell from lot SBMNH 357476 (52.3 mm ShL). The initial component of the shell clearly displays the features historically attributed to A. nouryi (numerous fine ribs, reduced keel tubercles and no apparent ears), while the later component, following the clear repair line, displays a transition to features historically attributed to A. cornutus (ribs reduced in number and more pronounced, keel tubercles reduced in number and of larger size, and initiation of ears). The presence of both shell types on a single shell clearly demonstrates that they represent different types of shell formation, not different argonaut species. This observation is supported by morphological evidence; despite full examination of nine female argonauts with shells (six historically identified as A. cornutus and three A. nouryi), no morphological characters could be found to separate specimens with different shell types (see Finn, 2013). The realisation that the two shell morphs represented two shell formation types, not two argonaut species, required that they be defined independent of previous species association: • Type 1 shell formation (historically attributed to A. cornutus shells) – formation of ears, few pronounced ribs, few large keel tubercles, appearance of more pronounced arch in the keel resulting in a tighter final whorl (i. e. increased ShB, reduced ApL). • Type 2 shell formation (historically attributed to A. nouryi shells) – absence of ears, numerous less pronounced ribs, numerous small keel tubercles, appearance of less pronounced arch in the keel resulting in the appearance of a shallower final whorl and elliptical shell (i. e. reduced ShB, increased ApL). An important character associated with Type 2 shell formation is inter-keel tuberculation (tubercles on the keel surface; see fig. 2 e). The appearance of inter-keel tuberculation on the keel of a shell flags a shift to Type 2 shell formation, while a loss of inter-keel tuberculation signifies a shift to Type 1 shell formation. Based on this realisation, it became clear that this large lot, and all other material examined of these shell morphs, belonged to a single species. Because A. nouryi Lorois, 1852, has date priority over A. cornutus Conrad, 1854; this study treats A. nouryi as the available name. See Finn (2013) for full synonymy. The key to understanding shell variation The realisation that individual shells may be composed of combinations of two types of shell formation provided the key to understanding the huge variation in shell shape across the single large collection of argonaut shells from Baja California. Combinations of sequential shell formation could be recognised in all shells and hence their varied appearance could be understood. Shells were recognised within this single lot that display a single type of shell formation plus those with one, two or three transformations between the two shell formation types. The initial whorl of most of the shells displayed Type 1 formation. Shell # 37 displays a single change from Type 1 to Type 2 shell formation (fig. 13). Shell # 72 displays a change from Type 1 to Type 2 shell formation and then a change back to Type 1 (fig. 14). Shell # 41 displays a change from Type 1 to Type 2 shell formation and then a change back to Type 1 and then to Type 2 (fig. 15). Damage to shells normally results in a conversion to Type 2 shell formation. In a transition between shell formation types, ears may be formed or subsumed. This is displayed across many shells within the lot. For examples, shell # 139 displays subsumed ears as a result of a transition from Type 1 to Type 2 shell formation (fig. 16), while shell # 136 displays ear formation, separate from the axis of the shell, as a result of a transition from Type 2 to Type 1 shell formation (fig. 17). Type material. Available type material for additional species synonymised with A. nouryi Lorois, 1852, was also examined for shifts in shell formation type. The holotype of A. dispar Conrad, 1854 (54.9 mm ShL, ANSP 129978) displays a single change from Type 2 to Type 1 shell formation (fig. 18). The holotype of A. expansus Dall, 1872 (80.2 mm ShL [P], USNM 61368), displays two changes – from Type 1 to Type 2 and then back to Type 1 (fig. 19). Shell thickness. Preliminary observations suggested that the shell walls of Type 1 formation are thicker than the walls of Type 2 formation. To investigate this phenomenon, a scanning electron microscope was used to examine variation in shell thickness across recognisable shell breaks that corresponded with a switch between shell types (a single damaged shell from lot SBMNH 357476 was sacrificed). Preliminary results indicate a reduction in shell wall thickness between Type 1 and Type 2 formation. Fig. 20 presents two scanning electron micrographs displaying a reduction in thickness across a break signifying transition from Type 1 to Type 2. Shell thickness on the lateral face drops from approximately 220 to 140 µm (fig. 20 a), while thickness at the keel drops from approximately 275 to 210 µm in this shell (fig. 20 b). A lack of material that could be fragmented for examination with a scanning electron microscope limited the extent to which this phenomenon could be investigated. The lots housed in the SBMNH collection are too valuable to be considered for this style of destructive investigation. A reduction in shell wall thickness may be related to producing a larger shell area with less shell material. The resulting thinner walled shell (Type 2) would therefore consist of less calcium carbonate and weigh less than an equivalently sized thicker walled shell (Type 1). The relative weights of the three shells presented in fig. 5 appear to support this theory. The Type 1 shell (cornutus-type voucher; 4.0 g) is 1.3 times the weight of the Type 1 / Type 2 shell (intermediate voucher; 3.1 g) and 1.7 times the weight of the Type 2 shell (nouryi-type voucher; 2.4 g), despite the shells having similar ShL. Weight (g) to length (mm) ratios of the three shells were: 1: 16 for the Type 1 shell (cornutus-type voucher); 1: 20 for the Type 1 / Type 2 shell (intermediate voucher); 1: 28 for the Type 2 shell (nouryi-type voucher). These ratios suggest that per gram of calcium carbonate, Type 2 shell production results in a shell 1.8 times the length of a Type 1 shell. To investigate this relationship across the lot, ShW was plotted against ShL with eared and earless shells distinguished (fig. 21). The scatter plot indicates a separation between eared and earless shells based on weight. This difference was analysed statistically to determine significance. Probability plots indicate that both ShW and ShL follow normal distributions. An ANCOVA was used to determine if the slopes of the regression lines, generated for eared and earless shells, were the same or different. Shell type (eared or earless) was the independent variable, ShW the dependent variable and ShL the covariate. The ANCOVA revealed that the slopes of the regression lines are not equal and hence a significant difference in weight exists between eared and earless shells (F (1, 136) = 86.7, p <0.001).	en	Finn, Julian K. (2018): Recognising variability in the shells of argonauts (Cephalopoda: Argonautidae): the key to resolving the taxonomy of the family. Memoirs of Museum Victoria 77: 63-104, DOI: 10.24199/j.mmv.2018.77.05, URL: http://dx.doi.org/10.24199/j.mmv.2018.77.05
03F74A577A6EFFC2D25FFE3CFD58FA10.taxon	description	The original description of A. hians [Lightfoot], 1786, refers to a single image in Rumphius (1705): plate 18, figure B (fig. 22 a), designated as a lectotype by Moolenbeek (2008) in the absence of type material. Shells of A. hians can be recognised by smooth lateral ribs and a keel that increases in width with shell growth. Inter-keel tuberculation is absent. Argonauta hians has long been recognised as displaying considerable variation in shell form. Voss and Williamson (1971) noted that “ In the series from Hong Kong the sides of the aperture at the umbilicus range from strongly eared or auriculate with very large few knobs on the keel to specimens with no trace of auriculation and with rather more numerous, smaller knobs ” (p. 105). They found that “ if the 30 shells are laid out graded from large few knobs and strong auricles to smaller, more numerous knobs and flat sides there is an even gradation with no breaks or sudden changes ” (p. 105). They concluded that all shells “ belong to the same species ” (p. 105). As part of this study, 274 A. hians shells were directly examined in museum and private collections in Australia, United States, Europe, South Africa and Japan. With knowledge gained from examining shells of A. nouryi, all shells from all sites were examined for an abrupt change in keel tubercle height or ears that had been formed or subsumed in single shells. Because inter-keel tuberculation is not expressed in argonaut shells other than A. nouryi, this character could not be used. Two shell formation types. Shells of A. hians were found to display two clear shell formation types: • Type 1 shell formation – few pronounced ribs, large prominent keel tubercles, formation of ears. • Type 2 shell formation – numerous less-pronounced ribs, small and greatly reduced, keel tubercles, absence of ears. These shell formation types are similar to those expressed in A. nouryi except that variation in the arch of the shell was not observed and inter-keel tuberculation was not present. This variation had been noted by Voss and Williamson (1971) who stated: “ The knobs on the keel are very large and prominent in the first half of the shell and may remain large on the last half or may become considerably smaller ” (p. 105). Two shells are presented as examples: • • A shell from the Philippines (79.6 mm ShL [P], BMNH unreg., “ Cuming, i. ”) (fig. 23). This shell displays a clear shift from Type 1 to Type 2 shell formation indicated by a reduction in the size and spacing of the keel tubercles, a reduction in the ratio of ribs to keel tubercles from approximately 1.5: 1 to 1: 1 and ears subsumed. A shell from the North West Shelf, Western Australia (53.0 mm ShL, WAM S 31510) (fig. 24). This shell displays a shift from Type 1 to Type 2 shell formation. This transition occurred when the shell was at a smaller size and hence the ears are less developed. The resultant aperture shape (fig. 24 c) is extremely similar to that observed in Type 2 A. nouryi shells; see fig. 5 c, ii for comparison. Variation also occurs between the opposing faces of individual shells, further highlighting the plasticity of shell characters in this species. A single shell is presented here as an example: • A shell from Madagascar (60.8 mm ShL, NMV F 164734, “ Madagascar ”) displays a large ear on the right side only; the left side is earless (fig. 25).	en	Finn, Julian K. (2018): Recognising variability in the shells of argonauts (Cephalopoda: Argonautidae): the key to resolving the taxonomy of the family. Memoirs of Museum Victoria 77: 63-104, DOI: 10.24199/j.mmv.2018.77.05, URL: http://dx.doi.org/10.24199/j.mmv.2018.77.05
03F74A577A6EFFC2D25FFE3CFD58FA10.taxon	materials_examined	Of the 274 A. hians shells examined, 41 can be attributed to A. boettgeri based on the above description. While it is possible to select a subset of shells possessing these characteristics, which in isolation appear distinct, examination of the entire range of material quickly dissolves the parameters on which this subset is based. All features mentioned above are variable in A. hians: ribs and keel tubercles can be numerous or scarce, pronounced or reduced, consistent across the shell or variable; ears can be present or absent, produced or subsumed, expressed on one side of the shell or both; the shell surface can be granular or smooth, pigmented or white. Two shells, displaying variation across the growth of the shell, are presented as examples: • A shell from the British Museum (76.1 mm ShL [P], BMNH unreg., locality unknown, “ B 698, t. ”; fig. 26). This shell displays an aperture shape and axial region consistent with the original description of A. boettgeri (fig. 22 b, c) yet defies the description of A. boettgeri by showing signs of possessing ears at an earlier growth stage. While the ears have been subsumed with a shift from Type 1 to Type 2 shell formation, only the keel tubercles on the right side show a reduction in size (fig. 26 b); the left keel tubercles have remained large (fig. 26 a). • A shell from Museums Victoria (25.0 mm ShL [P], NMV F 164767, locality unknown; fig. 27). This shell would historically have been attributed to A. boettgeri due to its small size and distinctive earless aperture. This shell displays a dramatic change in keel tubercle size and spacing associated with a shift from Type 2 to Type 1 shell formation, thus highlighting the plasticity of these characters. In the absence of any consistent and definable diagnostic shell characters (in combination with a lack of diagnostic morphological characters or distinct distributions; see Finn, 2013), no evidence exists to justify maintaining A. boettgeri as a separate species. Consequently A. boettgeri Maltzan, 1881, is treated here as a synonym of A. hians [Lightfoot], 1786. Insight from whole animals. As described in the Materials and Methods section above, a single specimen lot of 73 female A. hians, most with intact shells, exist in the collections of the Western Australian Museum and Museums Victoria. On initial examination, it was found that the lot included submature, mature and spawned (i. e. females with eggs attached to the central axis of the shell) individuals. The shells of the spawned females tended to show a shift to Type 2 shell production in the last components of the shells (all other shells were composed entirely of Type 1 shell production). This led to the consideration that shell shape and transformation may be triggered by changes in reproductive stage or condition. To understand the underlying cause of a change in shell formation type at the point of egg laying, a subset of 33 intact and measurable individuals were selected and fully measured. The subset included submature, mature and spawned individuals, with a size range of 13 – 27 mm DML and 21 – 36 mm ShL. Two larger females, also collected over the North West Shelf, were incorporated into the analysis to expand the size range (QM Mo 77789: 39.9 mm DML and 51.8 mm ShL; 28.7 mm DML and 38.9 mm ShL). Changes in shell morphometrics relative to animal size. Shell dimensions were plotted against DML to determine if the size of the shell relative to the size of the female changes between submature, mature and spawned individuals. Scatterplots against DML were generated for ShL, ShB, ApL, ApW, KW and EW. The scatter plots indicate a linear relationship between shell dimensions and animal size, with linear regressions returning coefficient of determination values (i. e. R 2 values) between 0.72 and 0.90 (see Table 1). No discontinuities were observed between the three maturity stages. Ontogenetic changes in animal morphology. Dimensions and characters of the female argonauts were plotted against DML to determine if the relative proportions of the female changes between submature, mature and spawned individuals. Scatterplots against DML were generated for MW, HW, FL and AL. The scatter plots indicate a linear relationship between animal dimensions, with linear regressions returning coefficient of determination values (i. e. R 2 values) between 0.76 and 0.88 (see Table 2). No discontinuities were observed between the three maturity stages. Ontogenetic changes in shell morphometrics. Shell dimensions and characters were plotted against ShL to determine if relative shell proportions change between submature, mature and spawned females. Scatterplots against ShL were generated for ShB, ApL, ApW, KW and EW. The scatter plots indicate a linear relationship between shell dimensions and characters, with linear regressions returning coefficient of determination values (i. e. R 2 values) between 0.74 and 0.96 (see Table 3). No discontinuities were observed between the three maturity stages. The scatter plots provided no evidence of a change in relative shell and animal proportions between submature, mature and spawned individuals. If the examined characters underwent dramatic transformation with changes in state of maturity, it was expected that discontinuities would be observed in the plotted data. It is apparent that the visual change in shell form observed across this lot was not reflected in the relative measurements of the individuals measured.	en	Finn, Julian K. (2018): Recognising variability in the shells of argonauts (Cephalopoda: Argonautidae): the key to resolving the taxonomy of the family. Memoirs of Museum Victoria 77: 63-104, DOI: 10.24199/j.mmv.2018.77.05, URL: http://dx.doi.org/10.24199/j.mmv.2018.77.05
03F74A577A7CFFC2D1FAFA58FB6FF8EE.taxon	description	Two types of A. nodosus shells exist in collections: a finer shell with more ribs and small rib tuberculations (fig. 29 a), and a coarser shell with fewer ribs and larger rib tuberculations (fig. 29 b). This variation has previously been used as justification for splitting A. nodosus into two species. Kirk (1885), in recognising the two forms, generated a new species name for the fine tuberculated and earless form (A. gracilis) to separate it from the coarse tuberculated and eared form (known to Kirk, 1885, as A. tuberculata Shaw). Robson (1932) recognised the two shell types as varieties, not separate species, stating: “ Though the shell of this species is clearly distinguished from its fellows by the rough tuberculations, there are evidently two well marked varieties – one with very large carinal knobs and coarse sculpture, the other with low knobs and fine sculpture ” (p. 200). Dell (1952) called this the “ nodosa - tuberculata complex ” 2 and described it as follows: “ Group 1. The shell is eared laterally and the tuberculations on the ribs are comparatively large – this is what has been called nodosa. Group 2. The edge of the lip comes off the previous whorl in an even curve without trace of an ‘ ear’. The tuberculations are much finer and more numerous than in Group 1 – tuberculata ” (p. 54). Dell (1952) considered both forms to belong to a single species. While both shell varieties are common, individual shells displaying an obvious shift between fine and coarse shell formation are extremely rare. A single shell from Moreton Bay, Queensland (109.1 mm ShL, QM Mo 14232) displays a transition from fine shell formation to coarse shell formation at a point of previous damage (fig. 30). While the later component of the shell possesses ears, it is not clear whether the earlier component was eared or earless. No obvious changes were noted in shell thickness, curvature of the keel or relative heights of sequential keel tubercles. Examination of a large number of A. nodosus shells found no examples displaying a marked change in keel tubercle height or ears that had been formed or subsumed. While eared and earless forms exist, transition between the two types appeared more gradual than the sudden transformation documented in smaller species. A shell in the British Museum (109.0 mm ShL [P], BMNH unreg., locality unknown, “ B 395, e. ”) displays an ear on only one side, clearly demonstrating the plasticity of this character in this species (fig. 31). 2 Following Finn (2013) it is necessary to correct the original spelling of A. nodosa to A. nodosus. In accordance with the International Code of Zoological Nomenclature, Article 34.2 “ the ending of a Latin or latinized adjectival or participial species-group name must agree in gender with the generic name with which it is at any time combined [Art. 31.2]; if the gender ending is incorrect it must be changed accordingly (the author and date of the name remain unchanged) ” (I. C. Z. N., 1999). As Argonauta is masculine “ from the final noun nauta (a sailor) ” (I. C. Z. N., 1999, p. 34) the species-group name must be changed from the feminine nodosa (- a feminine) to the masculine nodosus (- us masculine).	en	Finn, Julian K. (2018): Recognising variability in the shells of argonauts (Cephalopoda: Argonautidae): the key to resolving the taxonomy of the family. Memoirs of Museum Victoria 77: 63-104, DOI: 10.24199/j.mmv.2018.77.05, URL: http://dx.doi.org/10.24199/j.mmv.2018.77.05
03F74A577A40FFFED1FAFF08FDC5FB97.taxon	description	Shells of A. argo are extremely consistent in dimensions and sculpturing. The area that has caused the most confusion for naturalists defining the species has been the aperture edge. A. argo can display huge variation in the shape of the aperture edge near the axis. Note the variation in the aperture edge of the two shells presented in fig. 32. Unlike ear formation, this variation occurs on the edge of the lateral wall parallel with the longitudinal axis of the shell; it is not a lateral extension. The expression of the lateral ribs can vary slightly from fine to coarse, suggesting the presence of two varieties (fig. 32). Transition between fine and coarse shell formation on a single shell is extremely rare. An illustrated shell from Monterey, California (81.9 mm ShL, USNM 61374) displays a shift from finer to coarser shell formation at the point of earlier damage (fig. 33). Small A. argo shells can also display laterally protruding ears. A shell from Venezuela (51.4 mm ShL, USNM 122208) highlights the plasticity of this character, displaying an ear on only the right side (fig. 34). The varied size and shape of the keel tubercles on the opposing sides of this shell demonstrate the range of variability of these structures in this species.	en	Finn, Julian K. (2018): Recognising variability in the shells of argonauts (Cephalopoda: Argonautidae): the key to resolving the taxonomy of the family. Memoirs of Museum Victoria 77: 63-104, DOI: 10.24199/j.mmv.2018.77.05, URL: http://dx.doi.org/10.24199/j.mmv.2018.77.05
