Mulinia byronensis Gray, 1837

Signorelli, Javier H. & Pastorino, Guido, 2011, Revision of the Magellanic Mactridae Lamarck, 1809 (Bivalvia: Heterodonta), Zootaxa 2757, pp. 47-67 : 53-54

Mulinia byronensis Gray, 1837

( Figures 6–7 )

Mulinia byronensis Gray, 1837: 376 , fig. 33; Hanley, 1843: 35, pl. 10, fig. 38; Adams & Adams, 1856: 380; Dall, 1909: 274, 286–287; Carcelles & Williamson, 1951: 343.

Mactra byronensis d´Orbigny, 1846: 511; Reeve, 1854: pl. 15, fig. 77; Weinkauff, 1884: 101, pl. 34, figs. 3–4.

Mulinea byronensis Gray. Conrad, 1868: 31 .

Mactra byroni Weinkauff, 1884: 101 (nomen nudum).

Mactra byroneana Weinkauff, 1884: 101 (nomen nudum).

Mactra jousseaumi Mabille & Rochebrune, 1889: 106 .

Mactra pencana Philippi, 1893: 8 , pl. 1, fig. 2.

Mactra lotensis Philippi, 1893: 10 , pl. 3, fig. 8.

Diagnosis. Shell oval, elongated, dorsal margin delimited by a line from umbo to posterior end; short lateral teeth close to cardinals.

Description. Shell oval to trigonal, equilateral, compressed; dorsal margins curved; line from umbo to posterior end very clear; ventral margin curved; external surface smooth with irregular growth lines, brownish periostracum ( Fig. 6 A–H). Umbos prosogyrous, not inflated. Internally white with V-shaped pallial sinus of 1/3 of shell length; internal ligament in trigonal chondrophore ventrally developed. Right hinge with two anterior and two posterior lateral teeth, strong, each with one rounded cusp ( Fig. 7 A); two cardinal teeth on anterior side of chondrophore, posterior cardinal vertically oriented; Left valve with one anterior and one posterior lateral teeth ( Fig. 7 B), anterior cardinal tooth oblique in relation to dorsal margin. Ultrastructure of two layers, internal with cross lamellar complex and external with simple cross lamellar structure ( Fig. 7 C–D).

Type material. [ M. byronensis ] NHM 196324, 5 syntypes (figs. 6A–H); [ M. pencana ] MNHNC (unnumbered), holotype from Talcahuano, Chile (figs. 6I –K); [ M. jousseaumi ] MNHN (unnumbered), one syntype from Orange Bay (figs. 6L–M); [ Mactra lotensis ] MNHNC (unnumbered), holotype from Lota, Chile (figs. 6N–O).

Type locality. “South America ”.

Other material examined. Peru. Peru (NHM 1563, 2 complete valves). Chile. Valparaíso, Chile ( MLP 5355, 3 valves); Concepción, Chile (NHM s/n°, 4 valves); Talcahuano, Chile ( MACN 13804, coll. in 1923, 26 valves); Puerto El Hambre ( AMNH 34041, 1 valve); Magellanic Strait ( MLP 1848, 1 valve; MZUSP 13060, 3 valves; AMNH 34039, 1 valve; NHM 79.10.15.68, coll. by Coppinger on H.M.S. Alert). Argentina. Ushuaia, Tierra del Fuego ( MZUSP 22298, 2 valves, 1981).

Distribution. Peru to Ushuaia, Argentina.

Remarks. Weinkauff (1884) mentioned that Gray should have named this species Mulinia byroni or byroneana . However, these nominal taxa must be considered unjustified emendations. Mulinia byronensis is characterized by a more elongated shell than M. edulis . The posterodorsal line that delimits the posterior area in M. byronensis is absent in M. typica . Mactra jousseaumi , collected in Orange Harbor (Magellanic Strait) by the “Mission Scientifique du Cap Horn” ( Fig 6 L–M), and Mactra pencana ( Fig. 6 I–K) and Mactra lotensis ( Fig. 6 N–O), both described by Philippi (1893) living on the Chilean coast, are clearly synonyms.

Figures

FIGURE 6. Mulinia byronensis, A – H: Syntypes of Mulinia byronensis Gray (NHM N ° 196324); I – K: Holotype of Mactra pencana Philippi, 1893 (MNHNC unnumbered); L – M: Syntype of Mactra jousseaumi Mabille & Rochebrune, 1889 (MNHN unnumbered); N – O: Holotype of Mactra lotensis Philippi, 1893 (MNHNC unnumbered), scale bar = 1 cm.

FIGURE 7. Mulinia byronensis, A – B: hinge description by using the nomenclature developed by Bernard and Munier Chalmas, scale bar = 1 cm; C – D: Ultrastructure of the shell, C: general aspect, OL: outer layer, IL: inner layer; D: detail of the inner layer with the cross lamellar complex, scale bar = 100 µm.