Carditopsis flabellum ( 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 : 219-221

Carditopsis flabellum ( Reeve, 1843)

Figs. 8 A–P, 9F, Appendix 8

Cardita flabellum Reeve, 1843 : pl. 9, fig. 47.

Cardita flabellum— Reeve, 1844: 194.

Actinobolus flabellum Reeve—Adams & Adams, 1857: 487 .

Carditopsis flabellum Reeve—Smith, 1881: 43 ; Lamy, 1922: 360.

Cardita flabellum Reeve—Clessin, 1888: 13 , pl. 3, fig. 3.

Carditopsis flabellum Reeve, 1843 — Dall, 1903: 712; Soot-Ryen, 1959: 40. Carditella pallida duodecimcostata Melvill & Standen, 1912: 361 , pl. 1, figs. 19, 19a. Carditopsis flabellum flabellum ( Reeve, 1843) — Dell, 1964: 195, texfig. 3, no 2–3; Reid & Osorio, 2000: 136 (in part). Carditopsis flabellum malvinae (Orbigny, 1846) — Dell, 1964: 195 (non d’Orbigny). Carditopsis flabellum ( Reeve, 1843) — Ramorino, 1968: 204, pl. 2, fig. 2, pl. 6, figs. 2, 3.

Type localities: Valparaíso, South America ( Cardita flabellum ); Burdwood Bank, 56 fathoms [102 m] ( Carditella pallida duodecimcostata ).

Material examined: syntypes of Cardita flabellum ( NHMUK 196381), 4 syntypes of Carditella pallida duodecimcostata ( RSM 1921.143.712), and 58 lots (Appendix 8, Table 1 ).

Other published records: Chile ( Ramorino, 1968) (Appendix 8, Table 2 ).

Known distribution: Valparaíso [33ºS], Chile to Malvinas / Falkland Islands [54°S]. Lamy (1922) reported the species from Perú, although the source of this record is unknown. Living specimens: 5– 292 m.

Description: Shell small (maximum observed L = 5.8 mm), trigonal (H/L = 0.88 ± 0.04, n = 17), equilateral in smaller specimens, slightly inequilateral in larger specimens, somewhat inflated (W/H = 0.60 ± 0.07, n = 17), solid ( Figs. 8 A–L). Anterior end obliquely projected in larger specimens. Antero-dorsal and postero-dorsal margins straight in smaller specimens, sloping steeply at similar angles; postero-dorsal margin longer than the antero-dorsal one. Postero-dorsal margin concave in larger specimens. Anterior, ventral and posterior margins forming a wide continuous curve, which insensibly connects to the postero-dorsal margin, and originates a well marked angle at the junction with the antero-dorsal margin ( Figs. 8 A–H, K, L). Lunule and escutcheon large, wide, and deep ( Figs. 8 I, J). Beaks small, low, subcentrally located, orthogyrate ( Figs. 8 A–L). Prodissoconch large (450 to 530 µm in length); P-1 with a central depression and strong radial ribs in well preserved specimens; P-2 separated from teleoconch by a lamellate rim, expanding in wings anterior and posteriorly ( Figs. 8 I, J, O). Shell surface sculptured with 11–16 strong, rounded radial ribs (up to 18 ribs fide Ramorino, 1968) paved with juxtaposed scales; interspaces wider than ribs, with fine commarginal lamellae ( Figs. 8 A–F, P). Periostracum thin, brown-yellowish ( Figs. 8 A–C). Inner shell surface coincident with outer sculpture; inner margin crenulated ( Figs. 8 K, L). Pallial line entire, ill defined.

Hinge plate narrow ( Figs. 8 M, N). Right valve ( Fig. 8 N): anterior cardinal tooth (CA3) forming a well developed hook, with anterior (CA3a) and posterior (CA3b) parts elongated, similar in length; CA3a merged with dorsal margin. Posterior cardinal tooth (CP3p) solid, elongated, straight, well separated from CA3b. Anterior lateral tooth (LAI) narrow, elongated, with distal cusp. Posterior lateral tooth (LPIII) low, ill defined. Left valve ( Fig. 8 M): anterior cardinal teeth (CA2 and CA4b) straight, anteriorly directed, almost parallel to each other; CA2 high, strong; CA4b lower and narrower than CA2. Posterior cardinal tooth (CP2p) hooked, with anterior part small, conical, with subcentral cusp, posteriorly directed, and posterior part elongated, close to dorsal margin. Anterior lateral (LAII) and posterior lateral (LPII) narrow, elongated; the former close to shell margin. External ligament absent. Internal ligament strong, located on a large, triangular resilifer, between anterior and posterior cardinal teeth ( Figs. 8 M, N).

Anatomy (Fig. 9F): Mantle margin with a large inhalant-pedal aperture, and a small posterior exhalant opening. Transverse section of anterior adductor muscle small, reniform; transverse section of posterior muscle ovate, larger than the anterior one. Only inner demibranch present. Demibranch nearly rectangular in outline, composed of up to 35 filaments. Ascending lamellae three-fourths the height of descending lamella. Labial palps small. Foot with byssal groove.

Remarks: Carditopsis flabellum appears as a very variable species in shell outline: from nearly equilateral in small specimens to increasingly more inequilateral in larger specimens; more or less inflated; and with a variable number of radial ribs. This intraspecific variability only becomes evident studying large series of specimens. In fact, at the same locality, specimens with 11 to 15 ribs were found. In addition, this series of specimens shows some differences in the sculpture of P-2, which seem to be correlated with the state of preservation: well preserved specimens show radial ribs while others (eroded specimens?) have a mesh-like pattern; the continuity of this character is confirmed by the finding of specimens with intermediate conditions.

D’Orbigny (1845) reported Carditopsis flabellum as a synonym of Cyclocardia compressa . Hinge teeth and ligament placement reveal that they correspond to different species and genera.

Dell (1964) regarded Cardita malvinae d’Orbigny, 1845 as a subspecies of Carditopsis flabellum , and assigned to this taxa specimens collected by the R.V. William Scoresby at Malvinas / Falkland Islands. The study of these specimens (NHMUK 1964723) reveals that they actually correspond to C. flabellum and are not conspecific with d’Orbigny’s species (see below).

Figures

FIGURE 8. Carditopsis flabellum. A, B, G: Syntype of Cardita flabellum, Valparaíso (NHMUK 196381); C, H: Syntype of Carditella pallida duodecimcostata, Burdwood Bank, 102 m (RSM 1921.143.712); D – F, P: Cape Horn, 198 m (ZMB 103461); I: Cape Horn, 198 m (ZMB 103423); J, O: Cabo San Pío, 65 – 80 m (MLP 13717); K – N: Isla Becasses, 30 – 40 m (MLP 13719). A – F: Outer views; A, C, D, F: Right valve; B, E: Left valve; G, H, K, L: Inner views; G, K: Left valve; H, L: Right valve; I, J: Dorsal view; M, N: Detail of hinge plate; M: Left valve; N: Right valve; O: Prodissoconch; P: Shell sculpture. Abbreviations: 3 a, 3 b, 3 p, 4 b, 2 p = cardinal teeth; LAI, LAII = anterior lateral teeth; LPII, LPIII = posterior lateral teeth; L = ligament; D = central depression; R = radial ribs; W = wing. Arrow shows P- 1 / P- 2 boundary. Scale bars: A, B, D, E, G, K, L = 2 mm; C, F, H, J, M, N = 1 mm; I, O, P = 500 µm.