Carditella semen ( Reeve, 1843 )

Güller, Marina & Zelaya, Diego G., 2013, The Families Carditidae and Condylocardiidae in the Magellan and Perú – Chile provinces (Bivalvia: Carditoidea), Zootaxa 3682 (2), pp. 201-239 : 216-218

Carditella semen ( Reeve, 1843)

Figs. 7 A– O, Appendix 7

Cardita semen Reeve, 1843 : pl. 9, fig. 43.

Cardita semen— Reeve, 1844: 193.

Cardita semen Reeve—d’Orbigny, 1845: 581; Philippi, 1860: 158 ; Clessin, 1888: 51, pl. 5, fig. 3. Cardita naviformis Reeve—d’Orbigny, 1845: 580 (non Reeve, 1843). Actinobolus semen Reeve—Adams & Adams, 1857: 487 .

Cardium pygmaeum Philippi, 1860: 158 , pl.7, fig. 3a, b (non Donovan, 1799). Carditella semen Reeve—Smith, 1881: 43 ; Lamy, 1922: 357.

Carditella semen Reeve, 1843 — Soot-Ryen, 1959: 39.

Carditella tegulata Reeve, 1843 — Soot-Ryen, 1959: 40, pl. 1, fig. 11. Carditella semen ( Reeve, 1843) — Dell, 1964: 194, textfig. 3, no 7. Carditella tegulata ( Reeve, 1843) — Marincovich, 1973: 10, fig. 9; Guzmán et al., 1998: 68 (non Reeve, 1843).

Type localities: Mexillones, Desert of Atacama, Bolivia [sic] [= Mejillones, Chile], 3 fathoms [5.5 m] ( Cardita semen ); Isla Blanca [Atacama] ( Cardium pygmaeum ).

Material examined: 5 syntypes of Cardita semen ( NHMUK 1967585), and 18 lots (Appendix 7, Table 1 ).

Other published records: Chile ( Philippi, 1860 ; Lamy, 1922; Soot-Ryen, 1959, as C. tegulata ; Guzmán et al. 1998, as C. tegulata ) (Appendix 7, Table 2 ).

Known distribution: Islas Lobos de Afuera [07°S], Perú to Isla Blanca [27°S], Chile. Living specimens: 0– 12 m.

Description: Shell medium sized (maximum observed L = 11.5 mm), trapezoidal (H/L = 0.76 ± 0.04, n = 37), markedly inequilateral, somewhat inflated (W/H = 0.68 ± 0.08, n = 37), solid ( Figs. 7 A–E, G, H, J, K). Anterior end shorter and lower than posterior end. Antero-dorsal margin sloping, concave, forming a more or less marked angle at the junction with anterior margin. Anterior margin short, rounded, well differentiated from ventral margin, which is obliquely straight, projecting posteriorly. Posterior margin arched, sometimes obliquely truncated, twice the height of anterior margin, insensibly connected with ventral margin, and forming angulation at the junction with dorsal margin. Postero-dorsal margin straight, parallel to ventral margin, slightly sloping, longer than the anterodorsal margin in larger specimens ( Figs. 7 A–E, G, J, K). Lunule short, wide, sunken; escutcheon narrow ( Fig. 7 H). Beaks pointed, small, low, anteriorly located, anteriorly directed ( Figs. 7 B, C, E, H, J, K). Prodissoconch small (about 250 µm in length); P-1 with three depressions, P-2 separated from teleoconch by a low, wide rim ( Figs. 7 L, O). Shell surface sculptured with 12–16 strong, wide, rounded radial ribs, usually with stout, elongated nodules on the anterior part, and projected flat scales on posterior part; interspaces narrower than ribs, with fine, commarginal growth lines ( Figs. 7 A–F, I). Periostracum thick, brownish ( Figs. 7 A, C, D). Inner shell surface porcelaneous, with the posterior part usually stained in brown, sometimes evenly whitish ( Fig. 7 G). Inner margin crenulated, coincident with outer shell sculpture, more evident at posterior part ( Figs. 7 J, K). Pallial line continuous.

Hinge plate narrow; dorsal margin between beaks and lateral teeth finely granulated ( Figs. 7 M, N). Right valve ( Fig. 7 M): anterior cardinal tooth (CA3) forming a prominent hook, with anterior part (CA3a) narrow, elongated, close to dorsal margin; and a posterior part (CA3b) wide, high with proximal cusp, triangular at the base. Posterior cardinal tooth (CP5b) elongated, narrow. Anterior lateral (LAI) strong and low, with rounded distal cusp. Posterior lateral tooth (LPI) elongated, massive, relatively high. Left valve ( Fig. 7 N): with two small and divergent cardinal teeth, the anterior one (CA2) triangular at the base, ventrally directed; the posterior tooth (CA4b), elongated, oblique. Anterior lateral tooth (LAII) high, with subcentral cusp, close to dorsal margin. Posterior lateral (LPII) massive, elongated. External ligament short and wide, located in a nymph that extends one-third the length of postero-dorsal margin ( Figs. 7 H, J, K, O). Internal ligament minute, on a resilifer located in the dorsal half of hinge plate, above CA4b in left valve, and behind CA 3 in right valve ( Figs. 7 M, N).

Remarks: Carditella semen closely resembles C. naviformis in general shell outline and sculpture but differs in having a coarser sculpture and wider ribs (particularly the posterior ones). Additionally, the antero-dorsal margin is concave in C. semen (more evident in the left valve), and the anterior margin is more clearly defined. Carditella semen also has stronger lateral teeth, and a consistently smaller, not mammillate prodissoconch, with three distinct depressions in P-1.

The study of a large number of specimens of Carditella semen allowed to determine the ontogenetic variation: small specimens have an equilateral shell outline; the unequal growing of anterior and posterior ends results in larger specimens being somewhat inequilateral—such as the syntypes ( Figs. 7 A, D, G)—to markedly inequilateral ( Fig. 7 C).

The specimens reported by d’Orbigny (1845) from Arica, Chile, as C. naviformis (NHMUK 1854.12.4.762) actually correspond to C. semen .

Soot-Ryen (1959), Marincovich (1973) and Guzmán et al. (1998) identified specimens from northern Chile as Carditella tegulata . The reexamination of the specimens studied by Marincovich (1973: fig. 9, housed at LACM) reveals that they actually correspond to C. semen . The illustration provided by Soot-Ryen (1959: pl. 2, fig. 11) suggests that this specimen also corresponds to C. semen and not to C. naviformis as assumed by Dell (1964) and Reid & Osorio (2000). The same is valid for the record of C. tegulata by Guzmán et al. (1998: textfig.).

The types of Cardium pygmaeum were not found either at the MNHNCL or ZMB, where other material studied by Philippi is housed. However, the original description and illustration suggest that C. pygmaeum could be a senior synonym of Carditella semen [not of C. tegulata , as suggested by Coan (2003)]. Cardium pygmaeum Philippi, 1860 , is in turn a primary homonym of Cardium pygmaeum Donovan, 1799 .

Figures

FIGURE 7. Carditella semen. A, D, G: Syntypes of Carditella semen, Mexillones, 5.5 m (NHMUK 1967585); B, E, F, H – O: Iquique, intertidal (LACM 64 - 16); C: Arica (NHM 1854.12.4.762). A – E: Outer view; A – C: Right valve; D, E: Left valve; F, I: Detail of shell sculpture; F: Anterior end; I: Posterior end; G, J, K: Inner views; G, J: Right valve; K: Left valve; H: Dorsal views; L: Larva removed from adult; M, N: Detail of hinge plate; M: Right valve; N: Left valve; O: Prodissoconch and ligament. Abbreviation: R = rim. Arrow shows P- 1 / P- 2 boundary. Scale bars: A, B, D, E, G, J, K = 1 mm; C = 3 mm; F, I, O = 200 µm; H, M, N = 500 µm; L = 100 µm.