Flexopecten felipponei ( Dall, 1922 )

Oviedo, Loreley & Pastorino, Guido, 2023, Description of the early shell morphology of three species of Pectinidae (Mollusca: Bivalvia) from Argentina, Zootaxa 5361 (3), pp. 427-443 : 435

Flexopecten felipponei ( Dall, 1922)

Figure 3

Prodissoconch

The Prodissoconch-1 has a faint radial striation, without distinct commarginal growth lines, mean length is 81 µm (n = 2). The Prodissoconch-2 has thin commarginal growth lines, mean length of the P-2 is 197 µm (n = 2), and P-1/P-2 length ratio is 0.41 (n = 2) ( Table 3 , Fig. 3F ).

Nepioconch

The microsculpture of the LV is fine and presents regularly and densely distributed pits ( Fig. 3A, C, E ). The mean height of the LV is 1.97 mm (n = 2) and the height of the prismatic stage of RV is 1.93 mm (n = 2) ( Table 4 ).

The ctenolium develops during the prismatic stage; the AA has an auricle prismatic stage. The byssal notch (RV) is deep, the byssal sinus (LV) still incipient.

Post-nepioconch

Ribs begin to develop rather early underlying the pitted and prismatic layer, respectively. The left valve has 28 to 34 faint folds (n = 2), with primary and secondary ribs being difficult to distinguish; there are no scales ( Fig. 3A, B, C ). The microsculpture of the fold interspaces morphs into elongate pits that, towards the shell edge, become fine antimarginal ridges and gutters ( Fig. 3C ).

The posterior and anterior auricles of the LV, and the posterior auricle of the RV show similar microsculpture patterns, interrupted by prominent growth ridges. The posterior auricle is slightly longer than the anterior one (ratio AA/PA = 0.92) ( Table 4 ).

The free margin of posterior auricles is straight whereas the one in the anterior auricle is anteriorly inclined. Two well defined ribs start from the ‘auricle prismatic stage’ of the anterior auricle (n = 2) ( Fig. 3D ). The byssal notch becomes sinuous and the byssal sinus is more conspicuous than in the nepioconch. The active ctenolium presents three to four teeth (n = 2) ( Table 4 ). The umbonal angle is obtuse (α =100º) (n = 2) ( Table 4 ). The shell can be white or light yellow in color.

Figures

FIGURE 3. Flexopecten felipponei. A. Left valve. B. Right valve. C. Fold of Post-nepioconch of LV stage. D. Anterior auricle and byssal notch. E. Microsculpture of LV Nepioconch. F. Prodissoconch of RV. Scale bars: A= 1 mm; B= 1 mm; C= 200 µm; D= 400 µm; E = 80 µm; F=100 µm. All specimens from Fracasso Beach (42.39754S, 64.19199W), Chubut Province, Argentina (CNP-INV 4084).