Caryocorbula swiftiana (C. B. Adams, 1852 )

Arruda, Eliane P., 2020, Taxonomic revision of the recent marine Corbulidae (Mollusca, Bivalvia) from Brazil, Zootaxa 4851 (1), pp. 1-59 : 31-35

Caryocorbula swiftiana (C. B. Adams, 1852)

Figures 8 and 9

Corbula swiftiana C. B. Adams, 1852: 236–237 . Dall, 1881: 114. Dall, 1886: 314; pl. II, fig. 5a–5c. Dall & Simpson, 1900: 473. Clench & Turner, 1950: 347–348; pl. 48, fig. 1–2. Morris, 1973: 92. pl. 32, fig. 12.

Corbula (Cuneocorbula) swiftiana . Lamy, 1941: 229–230.

Corbula (Caryocorbula) swiftiana . Abbott, 1974: 539; fig. 6002.

Corbula barratiana C. B. Adams, 1852: 237–238 , not figured. Dall, 1881: 114. Dall, 1886: 313; pl. II, fig. 7, 7a–7c. Clench & Turner, 1950: 259; pl. 47, fig. 7–8.

Corbula (Caryocorbula) barratiana . Abbott, 1974: 539; fig. 6001.

Corbula kjoeriana C. B. Adams, 1852: 237 . Dall, 1886: 316; pl. 1, fig. 6, 6a and 6b. Clench & Turner, 1950: 298–299; pl. 47, fig. 1–2.

Corbula caribaea d’Orbigny, 1853 (in 1841–1853): 284; pl. 27, fig. 5–8. Morris, 1973: 91; pl. 31, fig. 7. Mclean, 1951: 115; pl. 23, fig. 8. Humfrey, 1975: 278; pl. 32, fig. 11. Cosel, 1986: 190–193; fig. 105a–150c.

Corbula (Cuneocorbula) caribaea . Dall & Simpson, 1900: 473. Lamy, 1941: 229.

Corbula (Corbula) caribaea . Warmke & Abbott, 1961: 207; pl. 43, fig. 43c. Altena, 1971: 73–77, fig. 23c–f. Rios, 1985: 269; pl. 94, fig. 1327. Rios, 1994: 291; pl. 99, fig. 1420. Rios, 2009: 584 [not figure that probably is a shell of Caryocorbula chittyana ]. Salvador et al., 1998: 1032.

Caryocorbula caribaea . Mikkelsen & Bieler, 2007: 386–387.

Aloidis caribaea . Carcelles, 1944: 290–291; pl. 13, fig. 102. Castellanos, 1967: 270; pl. XXV, fig. 6, 7 and 8.

Corbula (Caryocorbula) cf. lavalleana . Weisbord, 1964: 396–399; pl. 57, fig. 7–14 [not d’Orbigny, 1853 (in 1841–1853)].

Corbula (Caryocorbula) contracta . Warmke & Abbott, 1961: 207; plate 43, fig. A (not Say, 1822). Abbott, 1974: 538; fig. 5998 (not Say, 1822).

Corbula nasuta . Morris, 1973: 91–92; pl. 31, fig. 12 (not G. B. Sowerby, 1833).

Caryocorbula (Caryocorbula) nasuta . Forti, 1969: pl.7, fig. 1a–b (not G. B. Sowerby, 1833).

Type material examined. Corbula swiftiana C. B. Adams, 1852 . MCZ 186103 , lectotype designated by Clench & Turner (1950, p. 347–348; pl. 48, fig. 1–2) (validity of designation confirmed herein), open pair, 10.9 mm length, 6.5 mm height, Caribbean Sea: Jamaica, Kingston, east part of Kingston Harbor ( Fig. 8 A–B) . MCZ 155601 , paralectotypes, two open pairs, 19 right valves and 13 left valves, Caribbean Sea: U. S. Virgin Islands, St. Thomas .

Corbula barratiana C. B. Adams, 1852 . MCZ 186107, lectotype designated by Clench & Turner (1950, p. 259; pl. 47, fig. 7–8) (validity of designation confirmed herein), left valve, 8.6 mm length, 6.1 mm height, Caribbean Sea: Jamaica, Kingston Harbor ( Fig. 8 C–D).

Corbula kjoeriana C. B. Adams, 1852 . MCZ 186105 , lectotype designated by Clench & Turner (1950, p. 298–299; pl. 47, fig. 1–2) (validity of designation confirmed herein), right valve, 11.7 mm length, 7.1 mm height, Caribbean Sea: Jamaica: Kingston Harbon ( Fig. 8E ) . MCZ 155600 , paralectotypes, 2 right valves and 2 left valves, Caribbean Sea: U. S. Virgin Islands, St. Thomas .

Corbula caribaea d’Orbigny, 1853 (in 1841–1853). BMNH 1854.10.4.552/1, lectotype designated herein, open pair, the specimen closest to the original length measurement, 9.2 mm length, 5.6 mm height, Havana, Cuba ( Fig. 8F ) . BMNH 1854.10.4.552/2–13, paralectotypes, 4 open pairs and two right valves and 6 left valves. The only known text and plate of Caryocorbula caribaea were published in 1853 (see remarks), in which there is no mention of a type. The lot BMNH 1854.10 .4.552 of the Natural History Museum of London is registered as being the syntype lot purchased of d’Orbigny .

Additional material. See Appendix. Labeled as Corbula caribaea , Caryocorbula caribaea or Caryocorbula swiftiana . USA between Sanibel Island, Florida and Saint Thomas, American Virgin Islands. Haiti, Port-au-Prince. Brazil between Amapá State and Rio Grande, Rio Grande do Sul State. Uruguay between La Paloma, Rocha and Punta Ballena, Maldonado. Argentina, Bahia Blanca, Buenos Aires.

Diagnosis. Shell small, thin to thick; oval to trigonal and equivalve in specimens in pre-accretion stage, trigonal-elongated and subequivalve in thick one, with moderate to well produced pointed posterior rostrum. Posterior slope narrow and gently concave, set off by a low and rounded keel. Valve surface, excluding the posterior slope, strongly and regularly convex, except for a concavity in the median-ventral area, just anterior to the keel. Anterior dorsal margin continuous with broad and convex anterior margin; posterior dorsal margin often longer than anterior dorsal; posterior margin short, obliquely truncated; posterior margin with a sinuous outline and frequently extended further towards the posterior by the lateral siphonal plate; ventral margin generally strongly convex over 2/3 anterior and concave or straight near the posterior margin, or regularly convex throughout length. Sculpture different in both valves, constituted by irregular and low commarginal ribs and by small radially arranged pustules, frequently present on the umbonal area and the posterior slope.

Redescription. Shape. Shell small (length: 3.5–11.5 mm; height: 2.5– 10 mm), trigonal-elongated, heavy, moderately inflated to inflated, subequivalve, subequilateral to equilateral, with moderate to well developed pointed posterior rostrum, aligned with the anteroposterior shell axis. Posterior slope narrow and gently concave, set off by a low and rounded keel, like a sigmoid line extending from the umbos to the posterior end of the ventral margin; keel intersects or fades before reaching the ventral margin; posterior slope forming an obtuse angle with central slope. Valve surface, excluding the posterior slope, strongly and regularly convex, except for a concavity in the median-ventral area, just anterior to the keel; right valve larger and more inflated than the left. Umbos prosogyrous with beaks at about 35%–56% of shell length from anterior end. Escutcheon lanceolate or sublancelote, larger and longer in the right valve, generally flat, sometimes depressed, defined by a low and rounded elevation in right valve and by a slender radial rib in the left valve; this slender radial rib is formed by confluence and the abrupt decrease in height of the adjacent commarginal ribs.

Anterior dorsal margin straight to convex, ventrally moderately inclined, continuous with broad and convex anterior margin, the latter situated in the same plane as the median longitudinal shell axis; posterior dorsal margin straight or convex, ventrally inclined, often longer than anterior dorsal; posterior margin short, obliquely truncated; viewed from its inner surface, posterior margin with a sinuous outline and frequently extended further, towards the posterior, by the lateral siphonal plate; ventral margin generally strongly convex over 2/3 anterior and concave or straight and inclined dorsally near the posterior margin, or regularly convex throughout length.

Ornamention. Exterior surface whitish with light brown periostracum. Sculpture different on both valves, constituted by irregular and low commarginal ribs and by small radially arranged pustules, frequently present on the umbonal area and the posterior slope; commarginal ribs slender, regularly to irregularly spaced with bases narrower than interspaces in the left valve and rounded and with base width equivalent to intercostal spaces in the right valve. Inner surface smooth, generally white, yellow in some specimens.

Hinge. Hinge axis almost parallel to antero-posterior shell axis. Right valve with cardinal tooth below the beak, and a resilial socket moderately sunken under umbo, rarely deep behind; right cardinal tooth pyramidal, stout, with apex curved dorsally, isosceles-triangle-shaped when viewed laterally. Left valve with a deep trigonal cardinal socket just posterior to the beak, with lateral walls strongly or slightly wrapped around its opening, and a chondrophore projecting almost perpendicular to the plane of hinge plate when viewed from its dorsal side. Chondrophore broad, flattened or shallowly excavated and divided into anterior and posterior trigonal areas by a radial ridge; posterior margin of chondrophore with a stout, rounded, tooth-like knob. Trough on right valve for reception of left valve continuous with the hinge plate, extending around all margins of the valve, except on the posterior margin.

Muscle scars. Adductor muscle scars slightly impressed in the valve, nearly perpendicular or oblique in relation to antero-posterior shell axis in both valves; anterior adductor scar pear-shaped; posterior adductor scar rounded. Anterior pedal retractor muscle scar elongate; posterior retractor muscle scar rounded; anterior and posterior pedal retractor scar joining adductor scars. Pallial line far from free border in both shell valves, especially in anterior two thirds. Pallial sinus shallow extending to anterior edge of posterior adductor muscle scar and intersecting to anteroventral point of the posterior muscle scar.

Pre-accretion shell. Specimens in pre-accretion stage oval to trigonal, subequilateral to equilateral, equivalve; posterior margin truncated, comparatively longer than thick shells. Posterior slope keel intersects ventral margin. Sometimes exterior surface with whitish V-shaped stain at the umbo that vanishes as valve thickness increases. Radially arranged pustules present in central and posterior slope. Thin hinge plate with inconspicuous tooth-like knob. Pallial sinus absent.

Distribution. Caryocorbula swiftiana is recorded for all Western Atlantic coast, from Massachusets ( USA) to Argentina ( Mikkelsen & Bieler 2007). In Brazil, specimens were analyzed from the state of Amapa to municipality of Rio Grande, state of Rio Grande do Sul, from intertidal zone to 86 m. Specimens from Florida, Puerto Rico, Haiti, Uruguai and Argentina were also analyzed.

Remarks. The most common name attributed to Caryocorbula swiftiana is Corbula caribaea d’Orbigny, 1853 (in 1841–1853). The original publication dates of d’Orbigny bivalves described in Histoire physique, politique et naturelle de l’Ile de Cuba ” is uncertain. According to Aguayo (1943), the d’Orbigny report was originally published in French and subsequently translated into Spanish, and the French edition was issued in two text volumes and one volume of plates, named Atlas. The volumes of the French edition were published in small installments, whose individual dates have never been fully compiled ( Mikkelsen and Bieler 2001). The date most attributed to Caryocorbula caribaea is 1842. The only known text and plate of Caryocorbula caribaea were published in the 1853 edition. In this edition the date applied to the species is 1846. However, it is not known if this date refers to the date of publication of the original French installment. Until the publication dates of d’Orbigny articles are clarified, Caryocorbula swiftiana has priority.

Caryocorbula swiftiana shows the highest morphological variation among the corbulid species compared herein. This species can be recognized by its trigonal-elongate and inflated shell with a very pronounced posterior rostrum and a short and sinuous posterior margin. In some populations, the valve surface is highly convex in its anterior 2/3 region and slightly concave anterior to the keel. These characteristics vary greatly among populations and during the growth of the shell.

Tallarico et al. (2015) analyzed the spermatozoan ultrastructure and mitochondrial gene sequence of C. swiftiana specimens from São Sebastião municipality with different thicknesses and concluded that the specimens correspond to the same species. Like the smaller and thinner specimens studied by Tallarico et al. (2015), the specimens from São Sebastião analyzed in the present revision show a whitish V-shaped stain on the umbo ( Fig. 9C and 9 G–H), which vanishes as valve thickness increases and the hinge plate becomes expanded and thickens.

Thick shells of Caryocorbula swiftiana from Ubatuba and São Sebastião (north of the state of São Paulo) are peculiar in that they are generally shorter than 7 mm in length and have a more trigonal form ( Fig. 8 G–H). Specimens in pre-accretion stage lack a pallial sinus, the hinge plate is narrow with a resilial socket deeply retracted below to beak ( Fig. 9K ), the left hinge has a small or absent knob ( Fig. 9I ), the posterior shell margin is long with respect to shell height, and the shell has conspicuous pustulose radial sculpture ( Fig. 9 A–B, 9G–H). The size at which the shell thickens varies greatly among populations and even small shells (specimens <5 mm) can be very thick and inflated.

Specimens from further north of Ubatuba and further south of São Sebastião municipalities have larger, more elongated, and thicker shells, with regularly and strongly convex valves ( Fig. 8 I–L and 8Q–R). In some of these individuals, the resilium grow beyond the chondrophore and is fixed below it.

The causes of these differences are unknown but could be related to low primary productivity ( Saldanha-Corrêa & Gianesella 2008), finer sediments and patchy oxy-reducing conditions ( Furtado et al. 2008) observed in the litoral north of São Paulo State.

Other characteristics also vary among specimens of the same population, such as the width of the commarginal ribs and the shape of the chondrophore. Generally, the sculpture differs slightly between the valves. In the left valve, the commarginal ribs are narrower than their interspaces, whereas in the right valve the rib bases can be similar to or slightly larger than the intercostal spaces. In some specimens, the bases of the commarginal ribs near the umbo can be broader or narrower than those near to the ventral margin. The shape of the chondrophore can also vary. In some specimens the knob is more developed than in others. Further study is required to test for morphological variability versus cryptic species.

Because of such significant variability, the present synonymy list is long. Among the commonly reported synonyms for Caryocorbula swiftiana are Corbula caribaea d’Orbigny, 1853 (in 1841–1853), Corbula barratiana C. B. Adams, 1852 , Corbula chittyana C. B. Adams, 1852 , Corbula lavalleana d’Orbigny, 1853 (in 1841–1853), Corbula fulva C. B. Adams, 1852 and Corbula kjoeriana C.B. Adams, 1852 . Among these species, I consider Corbula chittyana and Corbula lavalleana , included in the Caryocorbula genus, to be valid, and the characters that distinguish these species from C. swiftiana are discussed there. Unfortunately, Corbula fulva could not be analyzed.

Corbula uruguayensis Marshall, 1928 , has also been considered a synonym of C. swiftiana ( Carcelles 1944; Castelanos 1967; Figueiras & Sicardi 1970; Rios 1994, 2009; Rosenberg 2009). However, C. uruguayensis is a specimen in pre-accretion stage of C. patagonica that has not yet undergone shell thickening. The pre-accretion shell of C. patagonica , compared with Caryocorbula swiftiana , has a more inequivalve shell, a sharp radial keel between the central and posterior slope, longer posterior margin, and less convex valve surface with more regularly spaced commarginal ornamentation.

According to Coan (2002), C. swiftiana should also be synonymized with Caryocorbula nasuta (G. B. Sowerby I, 1833) of which Corbula nuciformis G. B. Sowerby I, 1833 , is a synonym ( Coan 2002). When comparing the lectotypes of both species with C. swiftiana , I have observed that this species lacks marginal ribs near the ventral margin and a serrate edge, which are, however, present in some larger specimens of C. nasuta (> 12 mm) ( Coan 2002). None of the analyzed specimens of C. swiftiana reached the size of 18 mm registered for C. nasuta . The variability of the shell thickness of C. swiftiana has also been observed by Coan (2002) for C. nasuta . Overall, these relatively minor differences do not allow to make a clear distinction between C. nasuta and C. swiftiana and additional studies are needed to demonstrate whether the two species are synonymous.

Figures

FIGURE 8. Caryocorbula swiftiana (C. B. Adams, 1852). A–B. lectotype (Clench & Turner 1950) MCZ 186103. A. external view of complete shell from left valve. B. external view of complete shell from right valve. C–D. lectotype of Corbula barratiana C. B. Adams, 1852 (Clench & Turner 1950) MCZ 186107. C. external view of right valve. D. internal view of right valve. E. lectotype of Corbula kjoeriana C. B. Adams, 1852, (Clench & Turner 1950) MCZ 186105, external view of right valve. F. lectotype of Corbula caribaea d’Orbigny, 1853 (in 1841–1853), designated herein BMNH 1854.10.4.552/1, external view of complete shell from left valve. G–H. CIB 1057. G. external view of left valve. H. external view of right valve. I–L. CMPHRM 2313. I. external view of left valve. J. internal view of left valve. K. external view of right valve. L. internal view of right valve. M–P. CIB 1065. M. external view of left valve. N. internal view of left valve. O. external view of right valve. P. internal view of right valve. Q–S. José Carlos Tarasconi Private Collection 08/09.1994. Q. external view of left valve. R. external view of right valve. S. dorsal view. Scale bars: A–F = 3mm. G–S= 2mm. Legends: c= chondrophore. cs= cardinal socket. ct= cardinal tooth; k= knob; ke= keel lsp= lateral siphonal plate; ps= pallial sinus; rs= resilial socket. The pink color of figures I–L is the result of the dye used in the screening material.

FIGURE 9. Caryocorbula swiftiana (C. B. Adams, 1852). A–H. Specimens in pre-accretion stage. A–D. CIB 1165. A. external view of left valve. B. internal view of left valve. C. external view of right valve. D. internal view of right valve. E–F. CIB 1162. E. external view of left valve. F. external view of right valve. G–H. CIB 1074. G. external view of left valve. H. external view of right valve. I–L. Hinge of shells with different thickening. I. CIB 1165, left valve hinge of specimen pre-accretion stage. J. CMPHRM 2396, left valve hinge of specimen in post-accretion stage. K. CIB 1165, right valve hinge of specimen in pre-accretion stage. L. CMPHRM 2396, right valve hinge of specimen in post-accretion stage. Scale bars: A–F= 2mm; G–L= 1mm. Legends: c= chondrophore. cs= cardinal socket. ct= cardinal tooth; k= knob; rs= resilial socket.