Corbula dietziana C. B. Adams 1852

Corbula dietziana C. B. Adams, 1852

Figure 2

Corbula dietziana C. B. Adams, 1852: 235–236. Dall, 1881: 114. Dall, 1886: 314; pl. I, fig. 5, 5a, 5b. Clench & Turner, 1950: 274–275; pl. 47, fig. 5–6. Mclean, 1951: 115; pl. 23, fig. 6. Warmke & Abbott, 1961: 207–208. Humfrey, 1975: 278; pl. 32, fig. 10.

Corbula (Cuneocorbula) dietziana. Dall & Simpson, 1900: 473. Lamy, 1941: 232.

Corbula (Hexacorbula) dietziana. Altena, 1971: 77. Rios, 1975: 251; pl. 80, fig. 1206.

Corbula (Caryocorbula) dietziana. Abbott, 1974: 538; fig. 5999. Rios, 1985: 270; pl. 94, fig. 1332. Rios, 1994: 292; pl. 99, fig. 1425. Rios, 2009: 585

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

Corbula blandiana C. B. Adams, 1852: 234–235. Clench & Turner, 1950: 261; pl. 47, fig. 3–4.

Corbula cymella Dall, 1881: 115. Dall, 1886: 315; pl. I, fig. 7, 7a.

Corbula (Cuneocorbula) cymella. Lamy, 1941: 232.

Corbula (Caryocorbula) cymella. Abbott, 1974: 540, fig. 6012. Rios, 1985: 269–270; pl. 94, fig. 1331. Rios, 1994: 292; pl. 99, fig. 1424. Rios, 2009: 585 [not figure that probably is a thin shell of C. patagonica d’Orbigny, 1846 (in 1843–1847)].

Caryocorbula cymella. Mikkelsen & Bieler, 2007: 386–387 [not figure, in the page 387, that probably is a shell of Caryocorbula marmorata (Hinds, 1843)]

Type material examined. Corbula dietziana C. B. Adams, 1852. MCZ 155604, lectotype designated by Clench & Turner (1950, p. 274–275; pl. 47, fig. 5–6) (validity of designation confirmed herein), open pair, 10.3 mm length, 7.3 mm height, 6.3 mm width (Fig. 2 A–B). Caribbean Sea, Jamaica, Kingston Harbor along the Palisads SE of the city.

Corbula blandiana C. B. Adams, 1852. MCZ 177062, lectotype designated by Clench & Turner (1950, p. 261; pl. 47, fig. 3–4) (validity of designation confirmed herein), open pair, 11.9 mm length, 6.3 mm height, 4.3 mm width (Fig. 2 C–D). Caribbean Sea, Jamaica, Port Royal.

Corbula cymella Dall, 1881. USNM 64089, holotype by monotypy, one right valve, 14.0 mm length, 9.8 mm height (Fig. 2 E–F). United States of America, Florida, Gordon Key. According to Dall (1886), the original description was based in a single specimen.

Additional material. See Appendix. Labeled as Corbula sp. or Corbula dietziana. USA between North Carolina and Egmont Key, Florida; Brazil between Amapá State and Ilha Grande, Rio de Janeiro State.

Diagnosis. Shell moderate in size, thin to thick, subquadrate in pre-accretion stage, subtrigonal in thick one, inflated, inequilateral with well-developed pointed posterior rostrum. Posterior slope large, set off by a strong and sharp keel, more conspicuous in thin shells. Anterior dorsal margin short, concave, anterior margin broadly convex; posterior dorsal margin slightly convex, longer than anterior dorsal; posterior margin obliquely truncated forming an acute short rostrum with posterior end of ventral margin; ventral margin straight to slightly convex. Lunule very concave, generally with purple patch.

Nepioconch well distinguished mottled with red to brown patches with narrow and sharp commarginal ribs, intercalated with large and uniform width interspaces; mesoconch with radial bands with sculpture different between both shell valves.

Redescription. Shape. Adult shell heavy, moderated in size (length: 3–16.6 mm; height: 2–11 mm), subtrigonal, very inflated, inequivalve and inequilateral with well-developed pointed posterior rostrum, aligned with the anteroposterior shell axis. Posterior slope large set off by a strong and sharp keel that dies out before reaching the ventral margin; plane tangential to posterior slope forming a strong obtuse to almost straight angle with the plane tangential to central slope. Umbos high, prosogyrous with beaks at about 20%–35% of shell length from anterior end. Lunule not demarcated, very concave, generally with purple patch. Escutcheon flattened, very large in right valve, narrow in left, defined by a low and sharp ridge which disappears gradually.

Anterior dorsal margin short, concave, slightly ventrally inclined; anterior margin broadly convex; posterior dorsal margin slightly convex, ventrally inclined and longer than anterior dorsal; posterior margin obliquely truncated forming an acute short rostrum with posterior end of ventral margin; ventral margin straight to slightly convex. Lateral siphonal plate (made of calcified periostracum) rarely present, when present only in the left valve.

Ornamentation. Periostracum deciduous, dark brown, present only on the mesoconch. Mesoconch with radial band patches; large, rounded and high commarginal ribs and narrow interspaces in right valve and with narrow, low and rounded commarginal ribs and larger interspaces in the left valve. Inner surface smooth, white, brown or red with purple or white patches.

Hinge. Hinge axis parallel to the anterior-posterior shell axis in thick specimens. Right valve with cardinal tooth posterior to the beak and a resilial socket under sunken umbo; right cardinal tooth pyramidal, stout, with apex curved dorsally, equilateral-triangle-shaped when viewed laterally. Left valve with anterior cardinal socket posterior to the beak, deep with lateral walls slightly wrapping around its opening, and a narrow chondrophore weakly projecting with large and low posterior knob; very tick shells with enlarged resilium-like pit attached to lower surface of chondrophore in specimens bigger than 10–12 mm of length. Trough on right valve for reception of left valve continuous with the hinge plate, extending around all margins of the valve.

Muscle scars. Adductor muscle scars moderate to strongly well impressed, in oblique angle in relation to anterior-posterior shell axis in both valves; pear shaped anterior adductor muscle scar; posterior adductor rounded. Anterior pedal retractor muscle scar elongated; posterior retractor muscle scar rounded; anterior and posterior pedal retractor scar joining adductor scar. Pallial line far from valve margin, oblique in relation to the anterior-posterior shell axis (higher anterior, lower posterior). Pallial sinus not invaginated, forming a straight or convex line on both valves.

Nepioconch and pre-accretion shell. Nepioconch mottled with red to brown patches and sculpture equal in both valves constituted by narrow and sharp commarginal ribs, intercalated with large and uniform width interspaces. Specimens in pre-accretion stage subquadrate with keel more conspicuous than thick shells and with medial radial sulcus more conspicuous in the left valve; sculpture as in nepioconch; posterior end rostrum more acute and conspicuous; hinge axis oblique in relation to the anterior-posterior shell axis in both valves; right valve with cardinal tooth less conspicuous and without resilial socket in very thin shells; left valve with chondrophore less projecting than specimens in post-accretion stage.

Distribution. The specimens of C. dietziana analyzed were collected from off Cape Hatteras, North Carolina, USA to Ilha Grande, state of Rio de Janeiro, Brazil, from a depth of 2 to 182 m. In Brazil, the northernmost site of collection is in the state of Amapá.

Remarks. Specimens in pre-accretion stage of C. dietziana are similar to specimens in post-accretion stage of Caryocorbula marmorata and so it is difficult to distinguish between them in locations where they occur together. Comparing specimens of similar size of about 8mm length, C. dietziana has an anterior dorsal margin and a lunule more concave than Caryocorbula marmorata, and an anterior margin situated further below the median longitudinal shell axis.

Corbula dietziana has an identical shell to the East Pacific Corbula speciosa (Reeve, 1843) (Coan 2002, Coan & Valentich-Scott 2012), and further studies are needed to determine whether this similarity is restricted to the shell.