Carditella tegulata Reeve 1843

Carditella tegulata (Reeve, 1843)

Figs. 5A– O, 9E, Appendix 5

Cardita tegulata Reeve, 1843: pl. 9, fig. 48.

Cardita tegulata— Reeve, 1844: 194; Hupé, 1854: 318. Cardita tegulina [sic] [recte tegulata]—d’Orbigny, 1845: 581. Actinobolus tegulatus Reeve—Adams & Adams, 1857: 487. Carditella tegulata Reeve—Smith, 1881: 43; Lamy, 1922: 357. Carditella pallida Smith, 1881: 43, pl. 5, figs. 9, 9b.

Cardita tegulata Reeve—Clessin, 1888: 33, pl. 12, fig. 10. Erycinella (Carditella) pallida Smith, 1881 — Dall, 1903: 702. Carditella pallida Smith—Lamy, 1922: 355.

Carditella Pallida Smith, 1881 —dell, 1964: 193.

Carditella tegulata (Reeve, 1843) — Dell, 1964: 194, texfig. 3, no. 8; Reid & Osorio, 2000: 136, fig. 7J. Carditopsis flabellum flabellum (Reeve, 1843) — Reid & Osorio, 2000: 136 (in part) (non Reeve). Carditella tegulata Reeve, 1843 — Cárdenas et al., 2008: 230 (in part) (not fig 7.91). Carditopsis flabellum Reeve, 1843 — Cárdenas et al., 2008: 232, figs. 7.92–94 (non Reeve).

Type localities: Valparaíso, South America, 25 fathoms [46 m] (Cardita tegulata); Port Rosario, 2–30 fathoms [4– 55 m] (Carditella pallida).

Material examined: 3 syntypes of Cardita tegulata (NHMUK 1967583); 2 syntypes of Carditella pallida (NHMUK 1879.10.15.122-4), and 15 lots (Appendix 5, Table 1).

Other published records: none.

Known distribution: Valparaíso [33°S], Chile to Beagle Channel [55°S]. Although Dall (1909) reported C. tegulata as distributed from “Callao [Perú] to Valparaíso”, no formal records on the occurrence of this species in northern Chile or Perú are known. Living specimens: 10– 50 m.

Description: Shell small in size (maximum observed L = 7.0 mm), widely triangular (H/L = 0.87 ± 0.03, n = 31), equilateral to somewhat inequilateral, flat (W/H = 0.55 ± 0.04, n = 31), solid (Figs. 5A–L, O). Posterior end equal in height or slightly higher than anterior end. Anterior end sometimes slightly produced. Antero-dorsal margin long, descent straight to somewhat concave, forming a week angle at the junction with anterior margin. Anterior, ventral and posterior margins forming a continuous wide curve; ventral margin slightly expanded and truncated posteriorly. Postero-dorsal margin straight, as long as or longer than the antero-dorsal margin, sloping at a similar angle, forming well marked angle at the junction with posterior margin (Figs. 5A–L). Lunule and escutcheon elongated and narrow; lunule one-half the length of the escutcheon (Fig. 5 O). Beaks low, acute, subcentrally located, anteriorly directed (Figs. 5A–L, O). Prodissoconch eroded in studied specimens. Shell surface white, sculptured with 11–15 flat but strong radial ribs, paved with rectangular, juxtaposed scales; interspaces narrower than rib width, with fine commarginal lamellae (Figs. 5A–G, J). Periostracum thick, beige to pale-buff (Figs. 5A, B, D, E). Inner shell surface coincident with outer sculpture; inner margin crenulated (Figs. 5H, I, K, L). Pallial line continuous.

Hinge plate narrow (Figs. 5M, N). Right valve (Fig. 5N): anterior cardinal tooth (CA3) hooked, with anterior part (CA3a) narrow, merged to dorsal margin, and posterior part (CA3b) larger, triangular at the base; posterior cardinal tooth (CP5b) short and narrow, oblique, close to CA3b, parallel to nymph. Anterior lateral tooth (LAI) elongated, narrow, with distal cusp. Posterior lateral tooth (LPI) elongated, high, not clearly differentiated from shell margin. Left valve (Fig. 5M): with two small and divergent cardinal teeth, the anterior tooth (CA2) elongated, ventrally directed, the posterior one (CA4b) conical, with subcentral cusp. Anterior lateral tooth (LAII) high, with subcentral cusp, close to dorsal margin. Posterior lateral tooth (LPII) elongated, relatively narrow, with distal cusp. External ligament located on a nymph which extends for one-third the length of postero-dorsal margin (Figs. 5M– O). Internal ligament small, in a resilifer just below the beak, over the CP5b in the right valve, and behind CA4b, in the left valve (Figs. 5M, N).

Anatomy (Fig. 9E): Transverse section of anterior and posterior adductor muscles large, the anterior ovate, the posterior pyriform, slightly smaller than the anterior. Both inner and outer demibranchs, present, posteriorly fused with each other. Outer demibranch one-fifth of size of inner demibranch, with 24 filaments in the larger specimens; ascending and descending lamellae equally developed. Inner demibranch with 35 filaments in the larger specimen; ascending and descending lamellae almost equal in height. Foot with posterior byssal gland.

Remarks: Carditella pallida was originally differentiated from C. tegulata by the number of radial ribs ( 14–15 in the former, 11–12 in the latter), and the subcentrally located beaks. Reid & Osorio (2000) reported specimens from Estero Elefantes (45º55’S), with intermediate characters, suggesting that both names could refer to clinal variations of a single species. Our study of additional specimens allows us to confirm that Carditella pallida and C. tegulata are synonyms. The shell of this species varies from triangular and almost equilateral (similar to that described for C. pallida) to trapezoidal and inequilateral forms (corresponding to what was previously referred to as C. tegulata).

Examination of the specimen figured by Reid & Osorio (2000) as “ Carditopsis flabellum flabellum ” (NHMUK 20080555), reveals a well-developed external ligament, therefore corresponding to Carditella tegulata. However, another specimen from the same expedition and station (MNHNCL 169) actually corresponds to the species referred to by the authors.

Figure 5. Carditella tegulata. A, D, H, K: Syntype of Cardita tegulata, Valparaíso, 46 m (NHMUK 1967583); B, E: Syntype of Carditella pallida, Port Rosario, 4–55 m (NHMUK 1879.10.15.122-124); C, F, I, L, M– O: Playa Llonco, 30–50 m (MACN-In 39064); G, J: Bahía Tom, 14 m (LACM 73-72). A–G, J: Outer views; A–C, G: Right valve; D–F, J: Left valve; H, I, K, L: Inner views; H, I: Left valve; K, L: Right valve; M, N: Detail of hinge plate; M: Left valve; N: Right valve; O: Dorsal view. Abbreviations: 2, 3a, 3b, 4b, 5b = cardinal teeth; LAI, LAII = anterior lateral teeth; LPI, LPII = posterior lateral teeth; eL = external ligament; iL = internal ligament. Scale bars: A, B, D, E, G–L = 2 mm; C, F, M– O = 1 mm.

Cárdenas et al. (2008) identified valves from Golfo Corcovado, Chile as Carditopsis flabellum. Although described as “lacking an outer ligament”, the figures they provided, as well as the material they studied (MZUC 32643), actually has an external ligament. The morphological characteristics of these valves reveal that they correspond to C. tegulata. The specimen figured by Cárdenas et al. (2008) as C. tegulata, actually corresponds to C. naviformis; however, the other specimens from the same lot (MZUC 32641) do correspond to C. tegulata. Melvill & Standen (1912) described Carditella pallida duodecimcostata from Burdwood Bank. The study of the type specimens reveals that they are not members of the genus Carditella but Carditopsis (see under Carditopsis flabellum).