Trinitasia iheringi ( Dall, 1897 ) Dall, 1897

Signorelli, Javier H. & Pastorino, Guido, 2012, Taxonomic revision of Brazilian Mactridae Lamarck, 1809 (Bivalvia: Cardiida), Zootaxa 3245, pp. 30-53 : 33-35

Trinitasia iheringi ( Dall, 1897) new combination

Figures 2 A–D, 3A–H

Mactrella iheringi Dall, 1897: 123 ; 1902: 510, pl. 32, fig. 8; 1915: 62.

Mulinia kempfi Cauquoin, 1969b: 1175 , fig. 1.

Mactra iheringi ( Dall, 1897) — Rios, 1970: 196, pl. 57; 1975: 236, pl. 75, fig. 1130; 1985: 243, pl. 86, fig. 1211; 1994: 265, pl. 90, fig. 1293; 2009: 536, fig. 1487.

Mactrellona iheringi ( Dall, 1897) — Altena, 1971: 54, pl. 5, fig. 1–3.

Mactra inceri Petuch, 1998: 39 , figs. 7, 8, 11.

Diagnosis. Shell length up to 65 mm, anterodorsal margin concave; pallial sinus deep and V-shaped; left hinge with the V-shaped cardinal tooth almost fused with the anterior lateral tooth, dorsal edge prolonged.

Description. Shell trigonal to subcircular, inequilateral, strong, umbones prosogyrate, inflated; dorsal margin concave in front of umbones ( Fig. 2 A–B), anterior end rounded; escutcheon not defined, ventral margin convex; external surface smooth, maximum length measured 57 mm (MACN-In 1817). Internally white, left hinge with two short lateral teeth (AII & PII), with one cusp, cardinal tooth V-shaped composed of two simple divergent cardinals (2a & 2b) flanked by accessory lamella (4b) ( Fig. 2 I); right hinge with two anterior lateral teeth (AI & AIII) elongated and similar in size and shape, two posterior lateral teeth (PI & PIII), the ventral one larger and elongated; with two cardinal teeth (3a & 3b) unfused and fragile; a trigonal chondrophore ventrally developed complete the hinge plate ( Fig. 2 H); pallial sinus V-shaped and deep to about half shell length. Ultrastructure of the shell with an outer crossed lamellar layer of elongated crystallites arranged into lamellae; crystallites in adjacent lamellae differ in alignment by approximately 90–98°. Inner shell layer variably complex crossed lamellar ( Figs. 2 J–K).

Mantle cavity organs. Siphons entirely fused and covered by the periostracum ( Fig. 3 A), internal papillae observed along the length axis ( Figs. 3 B–C); body laterally compressed with a rounded and large foot ( Fig. 3 H); ctenidia composed of two elongated and lenticular demibranchs, inner demibranch larger ( Fig. 3 D) with a food groove over the ventral margin ( Fig. 3 E), not observed in the outer one; labial palps trigonal, moderately elongated but large in relation to ctenidia size ( Fig. 3 F–G).

Type material. [ Mactrella iheringi ] USNM 107632 , holotype, one LV; [ Mulinia kempfi ] MNHN unnumbered, two syntypes; [ Mactra inceri ] CMNH 47338 , holotype, length 35.5 m, width 41 mm; CMNH 47346–50 , four paratypes .

Type locality. São Paulo state, Brazil, collected by H. von Ihering.

Other material examined. Nicaragua Bragman's Bluff, Puerto Cabezas ( CMNH 47.338, holotype, length 35.5 m, width 41 mm; CMNH 47346–50, four paratypes). Brazil—Aracaju, ( MNRJ 724, 1406); Alagoas ( FURG 11134); Bahía ( FURG 11450, 27544); Caravelas ( MZUSP 13039); Alcobaça ( MNRJ 8536); Espírito Santo ( MZUSP 82659; FURG 15977); Amapá ( FURG 14838; 14128); Rio de Janeiro ( MZUSP 45110); Peruíbe ( FURG 37478); Cananeia ( MZUSP 22388); Guarujá ( MZUSP 15856); Iguapé ( MZUSP 22386); Ilha Cardoso ( MZUSP 44977); Peruíbe ( FURG 17258; MZUSP 15124, 15132, 15145, 22384, 22385, 34290, 44975, 44978, 44995, 45193, 80825); Ilha Grande ( MZUSP 77488, 84042); São Vicente ( MZUSP 80967); Santos ( USNM 465565, 152631; MZUSP 303, 44976); São Paulo ( MNRJ 2709; USNM 681901, 775649; FURG 31562; MZUSP 659, 22382, 22383, 22387, 22389, 22390, 46481, 77487); Ubatuba ( MZUSP 22372, 22373, 22374, 22375, 22376, 22377, 22378, 22379, 22380, 22381, 44969, 46789); Guaratuba ( MZUSP 15072, 22367); Paraná ( MZUSP 22368, 22369); Paranaguá ( FURG 5180); Praia do Saí, Paraná ( MZUSP 22370); Santa Catarina ( FURG 42979, 47887, 34350, 47655; MZUSP 4627) .

Distribution. From Puerto Cabezas, Nicaragua to Santa Catarina state, Brazil.

Remarks. The types of M. kempfi ( Figs. 2 C–D) and M. inceri , illustrated by Petuch (1998), coincide with Trinitasia iheringi . Mulinia kempfi was synonymized by Rios (1985, p. 243). The analysis of types confirmed this synonymy. When Petuch (1998) described M. inceri , he pointed out shell differences between his species and T. iheringi . They were a less elongated shell, slightly anterior to the midline umbo position, depressed lunule producing a noticeable concavity along the anterior-dorsal area and pallial sinus deeper in Petuch's species. However, those differences must be considered intraspecific and both names considered as synonyms. Trinitasia iheringi was included in different genera in the literature ( Dall 1897; Altena, 1971; among others); however, the shell characters suggest the new combination proposed here. It does not belong in Mactra as its type species has a more elongated shell with a hinge characterized by lateral teeth equal in size and shape and a shallower pallial sinus. The absence of concentric external ornamentation, the stronger lateral teeth, the V-shaped pallial sinus and the poorly defined escutcheon suggest that T. iheringi does not belong to the genus Mactrella . In addition, the absence of a well developed keel and differences in hinge morphology separate it from Mactrellona .

The genus Trinitasia , introduced by Maury (1928) from the Miocene of Trinidad, was described to include the species Thyasira sanctiandreae Maury, 1925 ( Fig. 2 E–F). This genus was placed in Lucinidae by Chavan in Moore (1969: N505). Later, Woodring (1982) placed it in Mactridae after the examination of additional material. He also examined additional material from two species considered synonyms of Trinitasia sanctiandreae . The first one was described by Weisbord (1929) as Dermatomya harrisi from Tubará formation of Colombia ( Fig. 2 G). The second was introduced a few months later by Anderson (1929) as Mactra ( Mulinia ?) atlanticola from the same locality. The shell characters observed on the three related fossil taxa coincide with those of the types of Dall. The new combination thus provides the first evidence of the Tertiary genus in the living fauna from Brazil.

Figures

FIGURE 2. Trinitasia iheringi (Dall, 1897). A – B. holotype (USNM 107632), LV; C – D: Mulinia kempfi Cauquoin, 1969 b, two syntypes (MNHN unnumbered); E – F: Thyasira sanctiandreae Maury, 1925, PRI 985, holotype (courtesy of the Paleontological Research Institution); G: Dermatomya? harrisi Weisbord, 1929, PRI 22913 (courtesy of the Paleontological Research Institution); scale bar = 1 cm; H – I: hinge description according to the nomenclature developed by Bernard & Munier Chalmas, scale bar = 1 cm; J – K: ultrastructure of the shell, I: general aspect of radial section of a LV from close to hinge to ventral margin, ol: outer layer, il: inner layer; K: detail of the outer layer with the cross lamellar structure, scale bar J = 200 µm, K = 100 µm.

FIGURE 3. Trinitasia iheringi (Dall, 1897). A – C: Scanning electron micrograph (SEM) of siphons, A, general aspect, B, transversal section, scale bar = 1000 µm, C, detail of papillae, scale bar = 200 µm; D – E: SEM picture of ctenidia, D, external view of inner demibranch, scale bar = 1000 µm E, detail of food groove, scale bar = 500 µm; F – G: SEM picture of labial palps, scale bar = 1000 µm; H: foot, scale bar = 1000 µm.