Mulinia exalbida Gray, 1837

Signorelli, Javier H. & Pastorino, Guido, 2011, Revision of the Magellanic Mactridae Lamarck, 1809 (Bivalvia: Heterodonta), Zootaxa 2757, pp. 47-67 : 58-60

Mulinia exalbida Gray, 1837

( Figures 11–12 )

Mulinia exalbida Gray, 1837: 376 , Hanley, 1843: 35; Adams & Adams, 1856: 380; Conrad, 1868: 31; Weinkauff, 1884: 100, pl. 34, fig. 1–2.

Mactra exalbida Gray. Reeve, 1854 : pl. 15, fig. 78.

Mulinia bicolor Bernard, 1983: 40 (non Gray).

Mactra cibaria Philippi, 1893: 9 , pl. 2, fig. 4.

Mactra calbucana Philippi, 1893: 9 , pl. 2, fig. 5.

Diagnosis. Shell oval, inequilateral; hinge plate anteriorly oriented; posterior end low, inflated, with a more defined angle; irregular growth lines protruded from external surface; pallial sinus circular, short and high.

Description. Shell oval, subcircular, inequilateral, strong, maximum length up to 73 mm; with irregular growth lines very well defined, protruded from external surface; periostracum thin, yellowish, commonly absent in the umbonal area; umbos prosogyrous, located approximately at midpoint of shell length, not in contact. Posterior dorsal margin rounded, convex behind umbos, descending gently to posterior end and merging into the ventral rounded margin with a much defined angle ( Fig. 11 A–B). Lunule and escutcheon not delimited by any ornamentation. Internally white; adductor muscle scars circular, conspicuous, similar in size and shape. Pallial sinus short, Ushaped, rounded and high ( Fig. 11 D). Hinge formula as typical for Mactridae , right valve lateral teeth short and very close to cardinals; anterior ventral lateral teeth with subnodular morphology not observed in more elongated dorsal lateral teeth. Cardinal teeth unfused, on anterior side of ventrally well-developed chondrophore; two posterior lateral teeth similar in size and shape ( Fig. 12 A). Left valve lateral teeth short but deep; cardinal teeth fused, Vshaped, flanked by accessory lamellae ( Fig. 12 B). Shell ultrastructure ( Fig. 12 C–D) coinciding with that of previous species analyzed ( Taylor et al., 1973).

Type material. [ M. exalbida ] NHM 1837.12.1.3688, holotype and one paratype (figs. 11A–D); [ M. cibaria ] MNHN (unnumbered), holotype from Magellanic Strait (figs. 11E–G); [ M. calbucana ] MNHNC (unnumbered) holotype from Calbuco, Chile (figs. 11H–L).

Type locality. “South America ” only mentioned in the original description.

Other material examined. Chile. South America (NHM 1962.1087, 2 valves); de los Reyes Island, Concepción (NHM, coll. by M. Orellana in 1976, 8 valves.); Calbuco ( MNHNC, 1 valve); Puerto Yates ( MLP 9386, coll. by Beaufils in 1898, 1 valve); Estero de los Elefantes (NHM (unnumbered, Raleigh Int. Expedition, Chile 98); 52° 21´S, 73° 33´W ( AMNH 137036); Magellanic Strait ( MNHNC, 1 valve without periostracum).

Distribution. Concepción, Chile, to Magellanic strait.

Remarks. Mulinia exalbida has been neglected in the 20th century South American literature ( Carcelles, 1950; Carcelles & Williamson, 1951) probably because of its indefinite original type locality. However, Mulinia exalbida is a valid species that inhabits the Magellanic Province with Mactra cibaria ( Fig. 11 E–G) and M. calbucana ( Fig. 11 H–L) as its synonyms. The morphology of the type material of both taxa (MNHNC) coincides with Mulinia exalbida .

Figures

FIGURE 11. Mulinia exalbida, A – D: Holotype of Mulinia exalbida (NHM 1837.12.1.3688), scale bar = 1 cm; E – G: Holotype of Mactra cibaria Philippi, 1893 (MNHNC unnumbered); H – L: Holotype of Mactra calbucana Philippi, 1893 (MNHNC unnumbered), scale bar = 2 cm.

FIGURE 12. Mulinia exalbida, A – B: hinge detailed according to the nomenclature developed by Bernard and Munier Chalmas, scale bar = 1 cm; C – D: Ultrastructure of the shell, C: inner layer with the cross lamellar complex; D: outer layer showing cross lamellar structure, scale bar = 100 µm.