A new genus of the ‘Pitar’ group (Bivalvia: Veneridae) from the Western Atlantic Ocean revealed by geometric morphometric analysisAbstract
Understanding shell morphology is central to taxonomic and evolutionary studies of bivalves. When traditional systematic studies find limitations in the recognition and classification of taxa, geometric morphometrics methods become a tool to tackle these uncertainties. Taxonomic difficulties are frequently found in systematics studies of the generally homoplastic Pitarinae (Venereidae). Recent contributions have proposed that Neogene-Recent South American species traditionally assigned to Pitar sensu stricto showed a distinguishable morphology that allowed separating them from that genus, including them in Proteopitar. In this contribution, we perform two morphometric analyses: elliptic Fourier analysis (EFA) and 2D landmark analysis with the aim of evaluating the intra- and interspecific variation of these taxa from the Western Atlantic Ocean included in Pitar s.s. to evaluate its doubtful generic assignments. EFA results show a highly variable outline in Proteopitar patagonicus, superimposed in the morphospace of all other taxa. The three analyzed groups, Pitar, Proteopitar, and extant Western Atlantic Ocean species, are statistically differentiable in hinge morphologies (landmark analysis), as corroborated by the Discriminant Function Analysis. The latter taxa are also distributed in a restricted portion of morphospace in EFA and along with the recognition of additional morphological differences allow us to define the new genus Jasypitar.
Key words
elliptic fourier analysis; landmark analysis; Pitar; Proteopitar; Jasypitar
INTRODUCTION
The Pitarinae Stewart, 1930 is the largest subfamily within the highly diverse Family Veneridae (Bivalvia), with more than 70 genera (Mikkelsen et al. 2006), a cosmopolitan distribution, and a stratigraphic range extending from Late Cretaceous to the Recent (Keen 1969). It is characterized by the presence of shells with smooth or commarginal sculpture, often smooth and glossy periostracum, cardinal teeth parallel (not radiating) on the right valve, anterior lateral tooth present, and usually smooth inner margin (Mikkelsen et al. 2006). Following the proposal of Alvarez et al. (2019), where the doubts regarding the use of Callocardiinae Dall, 1895 instead of Pitarinae Stewart, 1930 were discussed, we prefer to continue using Pitarinae as the name of the subfamily that includes the species of Pitar ss. As a reinforcement of this decision, in the most updated classification of venerids based on molecular phylogenies, proposed by Liu et al. (2022), Pitarinae is considered a valid group, separated from Callistinae Habe & Kosuge, 1967 which is synonymized with Callocardiinae.
The study of the southern South American Pitarinae began in the middle 19th Century with the contributions of d’Orbigny (1843, 1844) and Koch (in Philippi 1844). However, it was not until the beginning of the following century that von Ihering (1907) performed one of the most complete analyses of the fossil and extant mollusk species of South America, including this subfamily, and proposing that the Pitarinae of this region would be represented by Amiantis Carpenter, 1864 and Pitar Römer, 1857. The study of the Pitarinae from northern South America, Caribbean, and North America have a similar background with detailed revisions of the group performed by Römer (1857), Dall (1902), and Palmer (1927).
Pitar is one of the taxa with the most complex systematics due to its presumptive worldwide distribution and high diversity, having more than 30 extant species (Huber 2010). This genus dates back to the Late Cretaceous according to bibliographic references (Keen 1969, Skelton & Benton 1993) but a complete revision of the fossil and extant taxa is still lacking. The genus Pitar is highly homoplastic, which has increased the difficulty of performing an accurate systematic study. Jukes-Browne (1913) and Marwick (1938) argued about the characteristics of the genus, questioning whether the election of P. tumens (Gmelin, 1791, Recent, Senegal, pl. 8, Figs. 12-13) as its type species was proper or not due to the presence of several morphological differences with other members of Pitar. All these systematic issues are reflected in the intricate taxonomic history of the extant taxon Pitar patagonicus (d’Orbigny, 1844) from the southern West Atlantic Ocean, previously better known as P. rostrata (Koch in Philippi 1844) (junior synonym, see Alvarez et al. 2019), which was included in Pitar by von Ihering (1907) (see below). Another species from Argentina, the fossil P. mutabile del Río & Martínez, 1998 from the middle Miocene–late Miocene, is also placed in Pitar due to its similarities with P. patagonicus. Both taxa have several features in common (e.g., conic anterior lateral tooth in adults, lunule very wide in its central region which gives it a subcircular appearance, high hinge plates with thick cardinal teeth, grooved tooth 2a, and 4b separated from the nymph by a groove in all its extension) that are absent in Pitar tumens. Based on these differences and supported by a phylogenetic study, Alvarez et al. (2019) included these two species in their new genus Proteopitar. These authors also discussed the high intraspecific variation of the outline of both species, the extant species Pr. patagonicus being the most variable, with subquadrate, subtriangular, or subrounded outlines. This feature was taken into account in the name Proteopitar, alluding to the Greek sea-God Proteus, who was able to change his appearance at will. A third taxon was erected by von Ihering (1907), Pitar rostrata var. ortmanni, which was later synonymized with Proteopitar patagonicus by Aguirre (1994), synonymy subsequently validated by Alvarez et al. (2019).
Alvarez et al. (2019) also pointed out the notorious morphological differences between three species from the Western Atlantic Ocean traditionally assigned to Pitar [P. albidus Gmelin, 1791 (Caribbean Sea to northern Brazil), P. fulminatus Menke, 1828 (North Carolina, USA to Santa Catarina, Brazil), and P. palmeri Fischer-Piette & Testud, 1967 (Cabo Frio to Santa Catarina, Brazil) (distributions after Huber 2010)] and the type species of the genus, Pitar tumens, raising doubts about the inclusion of these American taxa in Pitar.
The main goal of this contribution is to analyze the intra- and interspecific variation of the taxa from the Western Atlantic Ocean formerly included in the genus Pitar to clarify their doubtful generic assignments, as well as to evaluate the possible presence of a new genus. In addition, we studied the extreme shell outline variation of the species within the genus Proteopitar to investigate its reliability as a character in systematic analyses.
The ZooBank Life Science Identifier (LSID) of this publication is: urn:lsid:zoobank.org:pub:83C065BF-5C02-461D-904E-073118AB3913.
MATERIALS AND METHODS
One hundred and thirty-nine left valves of species of Pitar and Proteopitar: P. tumens (4), P. albidus (12), P. fulminatus (22), P. palmeri (1), P. rostrata var. ortmanni (2), Proteopitar mutabilis (12), and Pr. patagonicus (86) were digitized (shell interior) with a Nikon digital SLR camera (Appendix). We examined shell shape variation through shape variables generated from two 2D geometric morphometric methodologies: outline and landmark (LM) analyses. For the outline analysis, the overall shape was studied by means of elliptic Fourier analysis (EFA; Kuhl & Giardina 1982) of the contour coordinates. The principles of the EFA methodology have been described by previous authors (Crampton 1995, Lestrel 1997). For each individual, chain codes were registered along the contour to calculate the elliptic Fourier descriptors (EFDs). The number of harmonics (n) was calculated following Crampton (1995) and the series was truncated at n=7 with an average cumulative power of 99.99% of the total average power. Based on the first harmonic ellipse, the different outlines were normalized regarding orientation, size, and starting point (Kuhl & Giardina 1982). Three of the four EFDs describing the first harmonic ellipse were constant for all the outlines (Crampton 1995) and were not included in posterior analyses. The software Shape 1.3v (Iwata & Ukai 2002) was used for all the EFA analyses. Subsequently, a Principal Component Analysis (PCA) of the Fourier coefficients was computed using PAST v3.25 (Hammer et al. 2001).
For the LM analysis, twelve landmarks were used to explore the morphological variation of the left hinge plate of the studied specimens. These landmarks were: (1) umbo position, (2) dorsal apex of the 2a and 2b teeth, (3) ventral apex of the 2a tooth, (4, 5) anterior and posterior apices of the ventral side of the 2b tooth, (6) dorsal apex of the 4b tooth, (7) ventral apex of the 4b tooth, (8) posterior end of the nymph, (9) dorsal apex of the AII tooth, (10, 11) anterior and posterior apices of the ventral side of the AII tooth, (12) anterior end of the lunule (Fig. 2b). The configurations were processed with tpsUtil v1.61 and tpsDig2 v2.30 (Rohlf 2017) and analyzed with MorphoJ v1.07a (Klingenberg 2011). Generalized Procrustes Analysis (GPA) was the alignment method employed. The analysis was followed by a PCA and, subsequently, a Discriminant Function Analysis (DFA) with a permutation test (1000 replications) was calculated. This analysis was implemented for three pairs of taxa: Proteopitar versus Brazilian Pitar species, Proteopitar versus Pitar s.s., and Brazilian Pitar species versus Pitar s.s.
Results of morphometric analysis (LM). a) Hinge morphospace generated by PCA, including PC1, PC2 and PC3. b) Comparison of the mean hinge configuration (grey lines) and the extreme configuration for each axis (black lines).
RESULTS
Geometric morphometrics
Outline analysis. The PCA performed with the Fourier coefficients shows three significant components that explain 89.29% of the total variation. Variation along the first component (PC1; 51.33%) corresponds to the elongation of the shell through its axis of maximum growth, ranging from triangular (more negative PC1 scores) to suboval shapes (more positive PC1 scores). The second component (PC2; 25.36%) highlights variation between outlines with large umbones and ventrally oriented anterior margins (more negative PC2 scores) and small umbones and anteriorly extended anterior margins (more positive PC2 scores) (Fig. 1). The third component (PC3; 12.59%) emphasizes minor changes in the concavity of the ventral and dorsal margins. Although in the PC1 there is a clear separation of the specimens of Proteopitar mutabilis from those of Pitar sensu stricto and the Brazilian Pitar species, there is no clear separation between specimens of Proteopitar patagonicus and all of the remaining species, because specimens of this last taxon occupy almost the entire morphospace. There is a minor overlap in the PC2, with most of the specimens of Pr. patagonicus dispersed along the negative values of this axis while Pitar s.s. and the Brazilian species of Pitar tend to be distributed in positive values. There are no differences in the morphospace distribution along PC3 among the specimens a priori assigned to Proteopitar, Pitar s.s., and the Brazilian Pitar.
Results of morphometric analysis (EFA). a) Analysis of the overall shell shape variation along the first three PC axes. b) Extreme configurations for each axis (doted lines) and its corresponding mean (entire line). S.D. (Standard Deviation).
Landmark analysis. The PCA results reveal three significant components that explain 70.59% of the shape variation. The first component (PC1; 44.58%) is related to changes in the distance between the teeth, inclination of the lunule, and length of the nymph. The second component (PC2; 17.19%) explains the variation in the inclination of the 4b tooth, length of the 2b, width of the AII and length of the nymph. The third component (PC3; 8.81%) shows differences in the length of the AII, width of the 2b, and length of the lunule (Fig. 2).
In the Landmarks morphospace, Proteopitar and the Brazilian species of Pitar are at opposite ends of the PC1 with a small overlay area, Pitar s.s. has negative values and partially overlaps with Proteopitar specimens. Negative values of PC1 are characterized by the following features: the nymph is larger, cardinal teeth are also shorter, AII is lamellar, the hinge plate is lower, the umbo is more backwardly placed, and the lunule is more horizontal. In the PC2, the main difference is observed at specific level, with Pr. mutabilis placed mostly along negative values, Pitar tumens, P. albidus and P. palmeri within positive values, whereas Pr. patagonicus and P. fulminatus are placed on both sides of the axis (Fig. 2). The main variation in PC2 is related to small changes in orientation of the cardinal and lateral teeth, being both more anteriorly inclined through positive values. Along the PC3 there is a clear distinction between the morphospace occupied by the two American groups (Proteopitar and Brazilian Pitar) and the African Pitar (Pitar s.s.), which is placed at extreme negative values. At positive values of this PC the lunule is larger, the AII tooth is less distant from the cardinal teeth, and the 2b tooth is thinner than those placed on negative values (Fig. 2).
The DFA shows significant statistical values (Mahalanobis and Procrustes distances), and the Permutation and Cross-Validation tests indicate a few misclassified specimens (Table I).
Taxonomy
Family Veneridae Rafinesque, 1815
Subfamily Pitarinae Stewart, 1930
Jasypitar nov. gen.
Type species. Venus albida Gmelin, 1791, Recent, Caribbean Sea to Northern Brazil. Middle Pleistocene, Goaigoaza clays, Carabobo, Venezuela.
ZooBank Life Science Identifier (LSID) - urn:lsid:zoobank.org:act:3347C132-D494-451F-A63A-66C32D3706B0
Other included species. Jasypitar fulminatus (Menke, 1828) n. comb., Pleistocene-Recent, North Carolina (USA) to Santa Catarina (Brazil). Jasypitar palmeri (Fischer-Piette & Testud, 1967) n. comb., Recent, Cabo Frio to Santa Catarina (Brazil), and Late Pleistocene, Chuy Formation, La Coronilla, Uruguay.
Stratigraphic Range. Middle Pleistocene–Recent.
Diagnosis. Low umbones, short and thin cardinal teeth, elongated AII tooth, and short nymph. Ventral margin of the hinge plate strongly concave below 2a tooth, and parallel to the lunule margin and the AII tooth.
Derivation of name. “Jasy” means Moon in Guaraní, a native language commonly spoken in Paraguay, eastern Bolivia, northeastern Argentina, and southern Brazil. Pitar is the original name of the genus in which the species of Jasypitar were included by previous authors, and a common suffix of many Pitarinae. The grammatical gender of Pitar is masculine, Jasy is an addition to it, so Jasypitar should be treated as masculine.
Remarks. The three species of the genus are well known taxa inhabiting the tropical Atlantic coast of North and South America and the Caribbean Sea (Rocha & Matthews-Cascon 2015). The oldest record for a taxon of this genus belongs to a juvenile specimen of Jasypitar albidus reported by Weisbord (1964, p. 291, pl. 42, Figs. 7, 8) from the Goaigoaza clays, Carabobo, Venezuela of a Middle Pleistocene age (Macsotay & Caceres Hernandez 2005). There are some Pleistocene mentions of J. fulminatus from Grand Cayman Island (Rehder 1962), Bermudas Island (Spencer’s Point Formation) (Richards et al. 1969) and a late Pleistocene record of J. palmeri from the Chuy Formation, La Coronilla, Uruguay, further south than its extant distribution (Rojas & Martínez 2016, Rojas et al. 2018).
Jasypitar and Pitar (type species P. tumens, Fig. 3a-c) are very similar in morphology, but it is possible to differentiate them by the lower and less inflated shells of Jasypitar, which also have a less prominent dorsal ligament, shorter nymphs, larger lunule, lower hinge plate, and the margin of the hinge plate, AII tooth and lunule are parallel to each other (Table II).
a), b) and c) Pitar tumens (Gmelin, 1791); MACN-In 40492; a) left valve, interior view; b) right valve, interior view; c) left valve, lateral view (Recent, Senegal). d), e) and f) Proteopitar patagonicus (d’Orbigny, 1844); NHMUK 1854.12.4.712, holotype; d) left valve, interior view; e) right valve, interior view; f) left valve, lateral view (Recent, Bahía San Blas, Buenos Aires, Argentina). g), h), i) and j), Jasypitar albidus (Gmelin, 1791); MACN-In 3141; g) left valve, interior view; h) right valve, interior view; i) left valve, lateral view; j) dorsal view (Recent, Kingston, Surrey, Jamaica); k), l), m) and n) Jasypitar fulminatus (Menke, 1828); MACN-In 2736; k) left valve, interior view; l) right valve, interior view; m) left valve, lateral view; n) dorsal view (Recent, São Sebastiao Island, São Paulo, Brazil). o), p), q), r), s) and t) Jasypitar palmeri (Fischer-Piette & Testud, 1967); MNHN_IM_2000-38651, holotype; o) left valve, interior view; p) right valve, interior view; q) left valve, lateral view; r) dorsal view (Recent, Grande Island, Rio de Janeiro, Brazil); s) and t), J. palmeri; FCDPI 4222; s) left valve, interior view; t) lateral view (Late Pleistocene, Chuy Formation, La Coronilla, Uruguay). Scale bar = 10 mm.
Jasypitar is distinguishable from Proteopitar (type species Pr. patagonicus, Fig. 3d-f) by its shorter nymph and cardinal teeth, lamellar AII, which is also placed closer to the cardinal teeth, lower hinge plate, more central umbo, more horizontal lunule, thinner 2a tooth, and the margin of the hinge plate, AII tooth and lunule all being parallel to each other. It is also notable that the portion of the dorsal ligament visible with closed valves is thinner than in Proteopitar, and that the pallial sinus is a little shorter (Table II).
Jasypitar albidus (Gmelin, 1791) n. comb.
(Fig. 3g-j)
1791 Venus albida Gmelin, p. 3287
1853 Dione albida (Gmelin), Deshayes, p. 68
1864 Venus albida Gmelin, Krebs, p. 95
1867 Caryatis albida (Gmelin), Römer, vol. 1, p. 91, pl. 14, Fig. 4
1885 Cytherea albida (Gmelin), Dall, p. 102
1901 Meretrix albida (Gmelin), Dall & Simpson, vol. 20(1), p. 485
1902 Pitaria albida (Gmelin), Dall, vol. 26(1312), pp. 370–371
1927 Pitaria (Pitaria) albida (Gmelin), Palmer, vol. 1(5), pp. 25-26, pl. 6, Figs. 17, 18, 20
1933 Cytherea (Dione) albida (Gmelin), Trechmann, vol. 70(823), p. 35
1934 Pitar albida (Gmelin), Johnson, vol. 40(1), p. 47
1936 Cytherea albida (Gmelin), Lermond, p. 8
1949 Pitar (Pitar) albidum (Gmelin), Morretes, vol. 7(1), p. 35
1951 Pitar (Pitar) albida (Gmelin), McLean, vol. 17(1), p. 80, pl. 16, Fig. 3
1964 Pitar (Pitar) albida (Gmelin), Weisbord, vol. 45(204), p. 291, pl. 42, Figs. 7-8
1975 Pitar albidus (Gmelin), Rios, p. 229, pl. 72, Fig. 1099
1994 Pitar albidus (Gmelin), Rios, p. 286, pl. 98, Fig. 1401
Description. Shell small to medium sized (common size 40 mm), subquadrate to subelliptic. Umbo slightly prominent placed at anterior quarter of total length. Lunule long, occupying almost the total length of anterior margin, narrow, flat or slightly convex, and limited by a very thin line. Nymphs short and smooth. Right valve with 3a lamellar, short, inclined backwards, subparallel to tooth 1 and joined to anterior lateral AIII; 1 triangular, slightly thicker, and higher than 3a; 3b subhorizontal, short, wide, bifid; AIII lamellar, smaller, and shorter than AI, which is triangular; channel that connects anterior lateral pit to cardinal pit deep and remarkably short. Left valve with 2a and 2b joined in an inverted V shape; 2a thin, lamellar, not grooved; 2b triangular, straight, and slightly higher than 2a; 4b short, slightly curved, higher in its middle region and separated from nymph by narrow groove; AII tall, lamellar in adults, close to cardinals. Margin of hinge plate, AII tooth and lunule parallel to each other. Dorso-posterior region of right valve with a groove for insertion of left valve. Right lunule margin with a groove for insertion of left valve. Scar of pedal retractor muscles joined to adductor scars. Pallial sinus triangular, short, ascending, and round-ended. Commarginal sculpture of growth lines.
Additional material examined. See Appendix.
Remarks. One of the differences between Jasypitar albidus and the other species of the genus is the periostracum colour, being chalky white in J. albidus, white with brown or yellow spots or markings in J. fulminatus, and pinkish white in the case of J. palmeri. Jasypitar albidus also has the narrowest lunule of the three species, which is less trigonal, and more compressed.
Jasypitar fulminatus (Menke, 1828) n. comb.
(Fig. 3k-n)
1791 Venus holosericea Gmelin, nomen oblitum, p. 3290
1828 Cytherea fulminata Menke, nomen protectum, p. 91
1844 Cytherea varians Hanley, p. 109
1844 Cytherea rubiginosa Philippi, p. 19, pl. 3, Fig. 2
1858 Cytherea holosericea Gmelin, Menke, p. 15
1890 Cytherea penistoni Heilprin, p. 142, pl. 8, Fig. 4
1902 Pitaria fulminata Menke, Dall, vol. 26(1312), p. 371
1926 Pitar fulminata Menke, Peile, vol. 17, p. 95
1954 Pitar fulminata Menke, Abbott, p. 414, pl. 39d
1967 Pitar (Pitar) varians Hanley, Fischer-Piette & Testud, p. 212
1971 Pitar (Pitar) fulminata Menke, van Regteren Altena, p. 67
1975 Pitar fulminatus Menke, Rios, p. 229, pl. 72, Fig. 1101
1994 Pitar fulminatus Menke, Rios, p. 286, pl. 98, Fig. 1403
1994 Pitar fulminatus Menke, Diaz Merlano & Puyana Hegedus, p. 81, Fig. 181
2006 Pitar fulminatus Menke, Denadai et al., vol. 6(3), p. 3, 10A–10C
2014 Pitar fulminata Menke, de Freitas Tallarico et al., p. 97, pl. 3.42
Description. Shell small to medium sized (common size 40 mm), subquadrate to subtriangular. Umbo slightly prominent placed at anterior quarter of total length. Lunule long, occupying almost the total length of anterior margin, narrow, flat or slightly convex, and limited by a very thin line. Nymphs short and smooth. Right valve with 3a lamellar, short, inclined backwards, subparallel to tooth 1 and joined to anterior lateral AIII; 1 triangular, slightly thicker, and higher than 3a; 3b subhorizontal, short, thin, bifid; AIII lamellar, strikingly smaller, and shorter than AI, which is triangular; channel that connects anterior lateral pit to cardinal pit deep and very short. Left valve with 2a and 2b joined in an inverted V shape; 2a thin, lamellar, not grooved; 2b triangular, straight, or slightly curved and slightly lower than 2a; 4b short, slightly curved, higher in its middle region and separated from nymph by narrow groove; AII tall, lamellar in adults, close to the cardinals. Margin of hinge plate, AII tooth and lunule parallel to each other. Dorso-posterior region of right valve with groove for insertion of left valve, another groove for insertion of left valve in lunule margin. Scar of pedal retractor muscles joined to adductor scars. Pallial sinus triangular, short, ascending, and round-ended. Commarginal sculpture of thin commarginal ribs.
Additional material examined. See Appendix.
Remarks. As Huber (2010, p. 732) proposed the name Cytherea fulminata is the valid name for this species, and it has to be considered as nomen protectum. Meanwhile, the previous name Venus holosericea Gmelin, 1791, p. 3290, has to be treated as nomen oblitum. Venus holosericea was never used by other authors, except Menke (1858, p. 15), who recognized the junior synonym of C. fulminata.
Jasypitar fulminatus is differentiated from the other members of the genus by the portion of the dorsal ligament that is visible from outside, being an intermediate stage between J. albidus, and J. palmeri. Besides its color, the ornamentation of the shell is different from the other two species, in the case of J. fulminatus it consists of thin commarginal ribs, whereas J. albidus has commarginal lines and J. palmeri thin lirae.
Jasypitar palmeri (Fischer-Piette & Testud, 1967) n. comb.
(Fig. 3o-t)
1967 Pitar (Pitar) palmeri Fischer-Piette & Testud, p. 212, pl. 4, Fig. 24-29
1994 Pitar palmeri Fischer-Piette & Testud, Rios, p. 287, pl. 98, Fig. 1404
2018 Pitar cf. palmeri Fischer-Piette & Testud, Rojas et al., p. 234
Description. Shell small sized (common size 30 mm), subtriangular. Umbo slightly prominent placed at anterior quarter of total length. Lunule long, occupying almost the total length of anterior margin, wide, flat or slightly convex, and limited by a very thin line. Nymphs short and smooth. Right valve with 3a lamellar, short, inclined backwards, subparallel to tooth 1; 1 triangular, thicker, and slightly higher than 3a; 3b subhorizontal, dorsally elongated, very wide, bifid; AIII lamellar, smaller, and shorter than AI, which is also lamellar; channel that connects anterior lateral pit to cardinal pit deep and very short. Left valve with 2a and 2b joined in an inverted V shape; 2a thin, lamellar, not grooved, slightly curved; 2b triangular, narrow, straight, and slightly lower than 2a; 4b short, slightly curved, higher in its middle region and separated from nymph by narrow groove; AII tall, lamellar, close to the cardinals. Margin of hinge plate, AII tooth and lunule parallel to each other. Dorso-posterior region of right valve with groove for insertion of left valve, another groove for insertion of left valve in lunule margin. Scar of pedal retractor muscles joined to adductor scars. Pallial sinus triangular, short, ascending, and round-ended. Commarginal sculpture of very thin lamellae.
Additional material examined. See Appendix.
Remarks. Fischer-Piette & Testud (1967) remarked that P. palmeri has no external ligament, a characteristic that separates this species not only from others of the Pitar group, but also distinguishes it from the rest of the venerids. We observed that the nymph of the type material of P. palmeri (MNHN_IM_2000-38651; Fig. 3o-r) is the shortest of the three species and the ligament is less developed externally than in the other taxa of the genus, but still visible. If we compare this condition among the three species, we can recognize that J. albidus has the largest nymph and the widest separation between valves in the ligament area, J. palmeri has the shortest nymph and the narrowest separation, and J. fulminatus has an intermediate stage for both characters. Another remarkable characteristic of J. palmeri is its shorter and more ascending pallial sinus (Fig. 3s).
DISCUSSION
As Huber (2010) stated, there are many Caribbean species doubtfully classified and the intraspecific variation of well-known species such as J. albidus (Gmelin, 1791) and J. fulminatus (Menke, 1828) have not been studied yet, which could lead to problems of misclassification. A geometric morphometric approach (using both methodologies, EFA and LM) is demonstrated to be an adequate tool to distinguish both intra- and interspecific variation as well as intergeneric differences in bivalves in recent years. There are many examples in the bibliography applying geometric morphometric methodologies to the evolutionary and systematic study of bivalves. Some examples of these studies include analysis of the variation through ontogeny (Márquez et al. 2010, Alvarez & Pérez 2016, Pérez & Santelli 2018); sexual dimorphism (Pérez et al. 2017a); ecological morphotypes (del Río et al. 2016, Collins et al. 2019); geographical morphotypes (Getino Mamet et al. 2021); anagenetic and cladogenetic changes (Boretto et al. 2014, Milla Carmona et al. 2018, Trovant et al. 2017); and systematics (Collins et al. 2013, Pérez et al. 2017b).
According to the results of the EFA, Jasypitar nov. gen. has short shells with subrounded to suboval outlines. This outline is similar to that of Pitar tumens. The distribution of these taxa is almost completely overlapped by the position in morphospace of the subrounded to suboval specimens of Proteopitar patagonicus, which means that it is not possible to differentiate them by their outline itself.
A similar situation occurs with the subtriangular specimens of Proteopitar mutabilis sharing their morphospace with specimens of Pr. patagonicus. The extremely variable outline of Pr. patagonicus, previously reported by Alvarez et al. (2019), clearly influences the EFA analysis, because its specimens are distributed in almost the entire morphospace. Alvarez et al. (2019) did not indicate differences between the outline of these taxa, but our results allow us to separate Jasypitar from Proteopitar based on the restricted area of the morphospace occupied by Jasypitar. In addition, Alvarez et al. (2019) used some outline features to distinguish Pr. mutabilis from Pr. patagonicus. In our results, Pr. mutabilis occupies a more restricted portion of the morphospace than Pr. patagonicus.
In terms of hinge configuration, the three genera Pitar, Proteopitar, and Jasypitar nov. gen. are easily distinguishable, as corroborated by the DFA. Proteopitar occupies a central position in the morphospace while Pitar and Jasypitar are found at opposite ends. The LM analysis showed that the main differences between Pitar s.s. and Jasypitar are that Jasypitar has lower umbones, which means a less sloped lunule, shorter and thinner cardinal teeth, a longer AII tooth, and a shorter nymph. As was indicated by Alvarez et al. (2019), differences based on hinge configuration are important among these genera, which agrees with our results, but are opposite to the proposals of Huber (2010), Rios (1975, 1985), Fischer-Piette & Testud (1967), who considered that all the studied species are members of Pitar.
The phylogenetic analysis performed by Alvarez et al. (2019) also corroborated the evolutionary differences among Proteopitar, Pitar, and the new genus Jasypitar, because they obtained these species included in three different clades. Proteopitar mutabilis and Pr. patagonicus constitute a unique clade with very high support, but Alvarez et al. (2019) questioned the inclusion of the Brazilian species J. albidus and J. fulminatus (here included in Jasypitar nov. gen.) in the genus Pitar as proposed by previous authors (Rios 1975, 1985, Huber 2010). Finally, Alvarez et al. (2019) recovered Jasypitar albidus and J. fulminatus as part of the same clade with high support values and sharing seven synapomorphies: umbo anterior; lunule length of two-thirds of total height; nymph short; tooth 3b two times longer than tooth 1; lateral margin of the nymph low; thinner valves; tooth 3a of similar height of the other cardinal teeth. In that phylogenetic analysis Pitar tumens is the earliest diverging taxon of the “Pitar clade”, where Proteopitar is the most derived genus being the sister taxon of Lamelliconcha, another American genus, with Jasypitar species occupying an early diverging position.
CONCLUSIONS
By means of geometric morphometric analysis on hinge configuration and the consideration of other morphological characters, such as low umbones; short and thin cardinal teeth; elongated AII tooth; short nymph; ventral margin of the hinge plate below 2a tooth strongly concave, and parallel to the lunule margin and the AII tooth; and an external ligament less visible than in Pitar and Proteopitar, we erect the new Western Atlantic genus Jasypitar to include J. albidus (Gmelin, 1791), J. fulminatus (Menke, 1828), and J. palmeri (Fischer-Piette & Testud, 1967). Our results agree with the previous phylogenetic results of Alvarez et al. (2019), in which Jasypitar, Pitar and Proteopitar are monophyletic. The identification of the new genus Jasypitar allows us to better understand the taxonomy of the Pitarinae, a taxonomically complex group that has long been misunderstood because of its wide distribution, abundant diversity, and highly homoplastic shells.
ACKNOWLEDGMENTS
We especially thank K.S. Collins and S.N. Nielsen for their helpful comments and suggestions that improved this work. We thank C.J. del Río for her assistance, and helpful comments on an early version of the manuscript. The authors are indebted to the curators who facilitated access to paleontological and biological collections: C.J. del Río (MACN-Pi), A. Tablado and M. Romanelli (MACN-In), and to V. Heros and P. Maestrati (MNHN) for the pictures of the holotype of J. palmeri. CONICET is acknowledged for the postdoctoral grant given to MJA. AR acknowledges PEDECIBA, and ANII FCE_1_2021_1_167109 research grant for financial support.
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Appendix
Appendix.| Collection number | Valves | Species | Locality | Province | Country | Formation | Age |
|---|---|---|---|---|---|---|---|
| CIRGEO-PI 2805p | 2 | Pr. mutabilis | Cantera a 7km Ea S. Julio | Tierra del Fuego | Argentina | Carmen Silva | middle Miocene |
| CIRGEO-PI 2867p | 2 | Pr. mutabilis | Puesto 26 | Tierra del Fuego | Argentina | Carmen Silva | middle Miocene |
| CPBA 15092 | 17 | Pr. mutabilis | Puesto Fracaso | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 12510 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 12512 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 12513 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 15514 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 12515 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 12516 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 12518 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 12519 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 12520 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 12522 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 17392 | 2 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14469 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14470 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14471 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14472 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14473 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14474 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14475 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14476 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14477 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14478 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14479 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14480 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14481 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14482 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14483 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14485 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14486 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14487 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14488 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14489 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 13284 | 1 | Pr. mutabilis | Punta Norte | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14462 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14463 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14465 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14466 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14467 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14468 | 1 | Pr. mutabilis | Pto. Pirámides/P. Valdés | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 12507 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 12508 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 12509 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 12511 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 12517 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 12487 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 12488 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14460 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 14461 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 15491 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 15492 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 15493 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 15494 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| CPBA 15495 | 1 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| MAS-Pi 1005 | 1 | Pr. mutabilis | Ea. La Juanita | Entre Ríos | Argentina | Paraná | late Miocene |
| MACN-Pi 6395 | 6 | Pr. mutabilis | Puesto San José Este | Chubut | Argentina | Pto. Madryn | late Miocene |
| NHMUK 1854.12.4.712 | 2 | Pr. patagonicus | Bahía San Blas | Buenos Aires | Argentina | - | Recent |
| ANSP 31131 | 1 | Pr. patagonicus | Plataforma Cont. Arg. | - | Argentina | - | Pleistocene |
| MLP 2482 | 13 | Pr. patagonicus | arroyo Las Brusquitas | Buenos Aires | Argentina | - | Holocene |
| MLP 26232 | 1 | Pr. patagonicus | Cerro de la Gloria | Buenos Aires | Argentina | - | Holocene |
| MLP 26253 | 1 | Pr. patagonicus | Mar Chiquita | Buenos Aires | Argentina | - | Holocene |
| MLP 26297 | 1 | Pr. patagonicus | Ea. Rincón de López | Buenos Aires | Argentina | - | Holocene |
| MLP 34020 | 1 | Pr. patagonicus | Cantera Atlántida | Buenos Aires | Argentina | - | Holocene |
| MLP 25946 | 1 | Pr. patagonicus | Ea. Rincón de López | Buenos Aires | Argentina | - | Holocene |
| MLP 2469 | 21 | Pr. patagonicus | Cno. La Magdalena a PI | Buenos Aires | Argentina | - | Holocene |
| MLP 33414 | 1 | Pr. patagonicus | Bahía San Blas | Buenos Aires | Argentina | - | Recent |
| MLP 26255 | 1 | Pr. patagonicus | Mar Chiquita | Buenos Aires | Argentina | - | Holocene |
| MLP 26252 | 1 | Pr. patagonicus | Mar Chiquita | Buenos Aires | Argentina | - | Holocene |
| MLP 26233 | 1 | Pr. patagonicus | Mar Chiquita | Buenos Aires | Argentina | - | Holocene |
| MLP 26234 | 1 | Pr. patagonicus | Mar Chiquita | Buenos Aires | Argentina | - | Holocene |
| MLP 26225 | 1 | Pr. patagonicus | Mar Chiquita | Buenos Aires | Argentina | - | Holocene |
| MLP 26254 | 1 | Pr. patagonicus | Mar Chiquita | Buenos Aires | Argentina | - | Holocene |
| MLP 2478 | 1 | Pr. patagonicus | Rawson | Chubut | Argentina | - | Recent |
| MLP 26251 | 1 | Pr. patagonicus | Mar Chiquita | Buenos Aires | Argentina | - | Holocene |
| MLP 2479 | 4 | Pr. patagonicus | arroyo Las Brusquitas | Buenos Aires | Argentina | - | Holocene |
| MLP 2476 | 16 | Pr. patagonicus | Bahía Sanguinetti | Santa Cruz | Argentina | - | Holocene |
| MLP 2480 | 27 | Pr. patagonicus | Bahía Sanguinetti | Santa Cruz | Argentina | - | Holocene |
| MLP 34421 | 1 | Pr. patagonicus | Balneario La Chiquita | Buenos Aires | Argentina | - | Recent |
| MLP 33805 | 1 | Pr. patagonicus | Los Pocitos | Buenos Aires | Argentina | - | Holocene |
| MLP 1829p | 1 | Pr. patagonicus | San Antonio Oeste | Río Negro | Argentina | - | Holocene |
| MACN-Pi 426 | 1 | Pr. patagonicus | Puerto San Julián | Santa Cruz | Argentina | - | Pleistocene |
| MACN-Pi 425 | 2 | Pr. patagonicus | San Jorge Gulf | Santa Cruz | Argentina | - | Pleistocene |
| MACN-Pi 6301 | 1 | Pr. patagonicus | Puerto Madryn | Chubut | Argentina | - | Holocene |
| MACN-Pi 6397 | 5 | Pr. patagonicus | Ezeiza | Buenos Aires | Argentina | - | Pleistocene |
| MACN-Pi 6444 | 1 | Pr. patagonicus | 25 Km east of SAE | Río Negro | Argentina | B. San Matías | Pleistocene |
| MACN-In 35353 | 28 | Pr. patagonicus | La Paloma | Rocha | Uruguay | - | Recent |
| MACN-In 1814 | 6 | Pr. patagonicus | Ubatuba | São Paulo | Brazil | - | Recent |
| MACN-In 14151 | 8 | Pr. patagonicus | Mar del Plata | Buenos Aires | Argentina | - | Recent |
| MACN-In 11191 | 16 | Pr. patagonicus | Puerto Militar | Buenos Aires | Argentina | - | Recent |
| MACN-In 21268 | 16 | Pr. patagonicus | San Matías Gulf | Río Negro/Chubut | Argentina | - | Recent |
| MACN-In 18306 | 172 | Pr. patagonicus | Puerto Quequén | Buenos Aires | Argentina | - | Recent |
| MACN-In 16577 | 38 | Pr. patagonicus | Mar del Plata | Buenos Aires | Argentina | - | Recent |
| MACN-In 16145 | 6 | Pr. patagonicus | Bahía Brigman | Buenos Aires | Argentina | - | Recent |
| MACN-In 12021 | 18 | Pr. patagonicus | Necochea | Buenos Aires | Argentina | - | Recent |
| MACN-In 11581 | 14 | Pr. patagonicus | Mar del Plata | Buenos Aires | Argentina | - | Recent |
| MACN-In 13041 | 6 | Pr. patagonicus | Quequén | Buenos Aires | Argentina | - | Recent |
| CPBA 6930 | 1 | Pr. patagonicus | arroyo Las Brusquitas | Buenos Aires | Argentina | - | Holocene |
| FCDPI 7545 | 6 | Pr. patagonicus | La Coronilla | Rocha | Uruguay | - | Late Pleistocene |
| FCDPI 6252 | 1 | Pr. patagonicus | La Coronilla | Rocha | Uruguay | - | Late Pleistocene |
| FCDPI 6619 | 1 | Pr. patagonicus | La Coronilla | Rocha | Uruguay | - | Late Pleistocene |
| MACN-In 3141 | 20 | J. albida | Kingston | Surrey | Jamaica | - | Recent |
| MACN-In 5010 | 4 | J. fulminata | Isla de Guayba | Río de Janeiro | Brasil | - | Recent |
| MACN-In 2736 | 38 | J. fulminata | Isla Sao Sebastiao | Sao Paulo | Brasil | - | Recent |
| MACN-6556 | 4 | J. fulminata | Isla Governador | Río de Janeiro | Brasil | - | Recent |
| FCDPI 4222 | 1 | J. palmeri | La Coronilla | Rocha | Uruguay | - | Late Pleistocene |
| MACN-In 40492 | 2 | Pitar tumens | - | - | Senegal | - | Recent |
| FMNH 296352 | 4 | Pitar tumens | - | - | Senegal | - | Recent |
