Ensis macha ( Molina, 1782 )

Giacomino, Sebastián & Signorelli, Javier H., 2021, Systematic redescription of Solen (Ensisolen) tehuelchus and Ensis macha (Bivalvia: Solenoidea) from Argentina, southwestern Atlantic Ocean, Zootaxa 4964 (3), pp. 541-558 : 548-550

Ensis macha ( Molina, 1782)

( Figures 3 , 4 , 5 )

Solen macha Molina, 1782: 178 , 348— Molina & Molina, 1789: 328; Mawe, 1822: 28; d’Orbigny, 1846: 505; Hupe in Gay, 1854: 369; Sowerby II, 1874 (in Reeve & Sowerby, 1843-1878): 203, pl. 6, fig. 28; Clessin, 1888: 26, pl. 8, fig. 5; Dall, 1909: 274; Melvill & Standen, 1914: 135.

Ensis macha Molina —Mörch, 1853: 7; Martínez y Sáez, 1869: 6, pl. 1, fig. 1; Bloomer, 1906: 18; Carcelles & Williamson, 1951: 346; Osorio & Bahamonde: 1970, 206; Reid & Osorio, 2000: 137, fig. 5M.

Solen scalprum King, 1832: 335 ; Mörch: 1853, 6; Sowerby II, 1874 (in Reeve & Sowerby, 1843-1878): pl. 3, fig. 12; Doering et al., 1881: 75; Clessin, 1888: 25, pl. 8, fig. 1; Ihering, 1907b: 317; Stuardo, 1969: 229.

? Solen gladiolus Sowerby I, 1839: 153 , pl. 43, fig. 4; Wood & Wood, 1857: 254, pl. 25, fig. 8a–8c; Mörch, 1853: 7; Philippi, 1887: 169, pl. 34, fig. 8.

Ensis luzonicus Dunker, 1862: 421 —Clessin, 1888: 31, pl. 12, fig. 7.

Solen poirieri Mabille & Rochebrune, 1889: 104 — Ihering, 1907b: 406.

Type material: Ensis luzonicus ( ZMB 108700, holotype, 77 mm) ( Fig. 3A–B ) and Solen poirieri ( MNHN-IM 2000-31622 , syntype) ( Fig. 3C–F ) are the only species for which type material has been found .

Types for Solen macha are lacking. Type region is the “Arcipelago di Chiloe” by original notes. Actually, this name refers to Chiloe Island , Chile .

Solen scalprus is lacking in the cabinets of NHMUK. The type area was given as “Patagoniae oras Orientalis (Sea Bear Bay)” southwest of Pingüino Island , Santa Cruz province, Argentina

Solen gladiolus types are also missing. The species was described from “S. America”.

Other material examined: Chile: Caulin Beach , North Chiloe ( MLP 5354 , dry, 3 specimens) ; Ancud, Chiloé Island ( CNP-INV 849 , dry, 10 specimens) ; Punta Arenas, Magellan strait ( CNP-INV, 1302, dry, 20 specimens) ; Magellan strait ( CNP-INV 295 , dry, 15 specimens; 856, dry, 30 specimens; 859, dry, 10 specimens; 861, dry, 10 specimens; 862, dry, 12 specimens) . Argentina: Río Negro : Punta Villarino, San Antonio Oeste ( MACN 13347 , dry, 2 specimens) ; San Antonio Este, port ( MACN 9379 , dry, 11 specimens) ; El Sótano, Golfo San Matías ( CNP-INV 294 , dry, 10 specimens; 858, dry, 12 specimens; 867, dry, 15 specimens; 871, dry, 20 specimens; 890, dry, 10 specimens; 1351, dry, 10 specimens) . Chubut: Gulf of San Matías , Puerto Lobos, ( CNP-INV 256 , dry, 30 specimens; 257, dry, 30 specimens; MLP 7397 , wet, 3 specimens) ; Riacho, Gulf of San José ( MACN 35357 , dry, 3 specimens; MLP 6747 , dry, 2 specimens) ; La Tapera beah, Gulf of San José ( CNP-INV 249 , dry, 35 specimens; 250, dry, 12 specimens) ; de los Pájaros Island , Gulf of San José ( MLP 3748 , dry, 2 specimens) ; Lat. 41°04’ South Long. 65°03’ West ( MACN 18396 , dry, 1 specimen) ; Fracasso beach, Gulf of San José ( CNP-INV 231 , dry, 50 specimens; 232, dry, 50 specimens) ; Villarino, Gulf of San José ( CNP-INV 838 , dry, 30 specimens; 840, dry, 30 specimens, 277, dry, 15 specimens) ; Puerto Pirámides ( MLP 4156 , dry, 1 specimen) ; Bahía Camarones ( CNP-INV 285 , dry, 20 specimens; 843, dry, 20 specimens; 846, dry, 20 specimens; 870, dry, 20 specimens; 877, dry, 20 specimens) ; Bahía Bustamante ( CNP-INV 1308 , dry, more than 50 specimens; MACN 26443 , dry, 8 specimens) ; Comodoro Rivadavia ( CNP-INV1307 , dry, 30 specimens; MACN 1960 , dry, 6 specimens; MACN 6583 , dry, 96 specimens; MLP 2069 , wet, 6 specimens; MLP 10244, dry, 13 specimens) ; Rada Tilly ( MACN 14441 , dry, 65 specimens) ; Gulf of San Jorge , Alsina beach ( CNP-INV276 , dry, 10 specimens; 850, dry, 14 specimens; 852, dry, 10 specimens; 876, dry, 20 specimens; 883, dry, 30 specimens; 842, dry, 20 specimens; 851, dry, 25 specimens; 853, dry, 22 specimens; 854, dry, 12 specimens) . Santa Cruz: del Fondo Bay ( MLP 2702 , dry, 1 specimen) ; Caleta Olivia, Golfo San Jorge ( CNP-INV 291 , dry, 10 specimens) ; Mazarredo, Gulf of San Jorge ( CNP-INV 289 , dry, 20 specimens) ; Puerto Deseado ( MACN 29507 , dry) ; Punta Buque, Puerto Deseado ( CNP-INV 287 , dry, 30 specimens) ; Puerto San Julián ( CNP-INV 1304 , dry, 10 specimens; MLP 1877 , dry, 20 specimen; MLP 1874 , dry, 3 specimens) ; Monte León, NP, ( CNP-INV 277 , dry, 20 specimens; 278, dry, 22 specimens) ; mouth of Río Gallegos ( MLP 1878 , dry, 11 specimens) . Tierra del Fuego: Malvinas / Falkland Islands ( MACN 10158 , dry) ; Buen Suceso Bay ( MLP 6829 , dry, 2 specimens) ; Puerto Roca, Staten Island ( MACN 21986 , dry, 1 specimen) ; San Pío Cape ( MACN 23890 , dry, 1 specimen) ; Canal del Beagle , Puerto Almanza ( CNP-INV 286 , dry, 10 specimens; 845, dry, 10 specimens; 847, dry, 15 specimens) ; Ushuaia ( MACN 4059 , dry, 1 specimen; MACN 23607 , dry, 2 specimens) .

Diagnosis: Shell up to 211 mm long, anterior end rounded and posterior end almost straight; dorsal margin concave and ventral margin convex; anterior adductor scar bigger than the posterior one, lentiform, elongated, projecting postero-ventrally; posterior adductor oval, close to the dorsal margin.

Description: Shell length up to 211 mm approximately (MACN 10158), equivalve, inequilateral, cylindrical; ( Fig. 4A–D ); anterior end rounded, posterior end slightly straight; umbo anteriorly placed; dorsal margin slightly concave and ventral one moderately convex ( Fig. 4A–B ); external surface smooth or presenting growth lines; brownish to yellowish periostracum, usually eroded ( Fig. 4A–B ); internal surface white to violet ( Fig. 4C–D ).

Anterior adductor muscle scar bigger than the posterior one, lentiform, elongate, projected inside the mantle cavity ( Fig. 4C–D, H ); posterior adductor muscle scar oval, close to the dorsal margin ( Fig. 4C–D ); pallial line elongated, antero-ventrally, postero-ventrally and postero-dorsally projected ( Fig. 4C–D ); pallial sinus shallow ( Fig. 4C–D ).

Hinge plate like genus diagnosis ( Fig. 4E–F ), the horizontally oriented teeth are four to six times longer than the vertically oriented, the teeth of the right valve fitting between the 2 of the left valve; dark ligament, opisthodetic ( Fig. 4G ).

Mantle Cavity Organs. Three mantle folds, pellucid; ctenidia type C(2a) of Atkins (1937), eulamelibranch, formed by two demibranchs, one left and one right, placed across the antero-posterior axis, each demibranch with one inner descending arm and one outer ascending arm, both arms equal in length and width ( Fig. 5A ), food groove positioned on the distal edge of each demibranch ( Fig. 5G ); two pairs of labial palps, large, up to 6 mm of length, slightly longer than wider, inner surface plicate and outer smooth ( Fig. 5F ); foot highly developed, elongated, pedal groove observed ( Fig. 5A, E ); anterior adductor muscle antero-ventrally elongated, lentiform ( Fig. 5C ); posterior adductor muscle smaller, circular ( Fig. 5D ); siphons type B of Yonge (1982) very short, separate, only fused in the basal region, incurrent siphon bigger than the excurrent one, base of both siphons surrounded by three rows/categories of tentacles, the external crown with 23–25 conical, rounded tentacles, the intermediate crown with 26–28 smaller, and the inner crown with the smallest tentacles, surrounding each siphon separately, incurrent siphons with three categories of tentacles on the aperture ring, excurrent siphon without tentacles on the edge of aperture ring ( Fig. 5B ).

Distribution: Specimens of E. macha from Chiloe, Chile to San Antonio Oeste, Argentina, were examined. However, its distribution range is usually mentioned to the coasts of Peru ( Osorio & Bahamondes 1970; Paredes et al. 2016; Valentich-Scott et al. 2020; Zaixso et al. 2015, among others). This range must be restricted after the genetic studies that revealed two genetic units ( Márquez et al. 2020; Vierna Fernández 2014). The southern unit, distributed from Chiloe in the Pacific to San Antonio Oeste, in the Atlantic, must be attributed to Ensis macha and the northern unit, from Tubul, Chile to northern Peru to a new species, currently in process of description ( Márquez et al. 2020).

Habitat: shallow waters (5–30 m depth) of muddy and sandy bottoms ( Barón et al. 2004).

Remarks: Solen macha Molina, 1782 , is the original combination proposed by the author on pages 178 and 348 (description) of his “Historia Natural de Chile ”. Many authors included E. macha in Solen ( Küster & Clessin 1842 -1889; d’Orbigny 1846; Dall 1909; Hupe in Gay 1854; Mawe 1822; Melvill & Standen 1914; Sowerby II 1874, in Reeve & Sowerby 1843-1878).

Four junior synonyms of Ensis macha were checked and confirmed. They are Solen scalprus King, 1832 , Solen gladiolus Sowerby I, 1839 , Ensis luzonicus Dunker, 1862 , and Solen poirieri Mabille & Rochebrune, 1889 . Solen scalprus and S. poirieri were described based on juvenile specimens. Although type material of Solen scalprus was not found, its type locality and hinge description confirmed it as a junior synonym of E. macha . Martínez y Sáez (1869) considered Solen gladiolus as a junior synonym of E. macha . The type material has not been found in the NHMUK, but the original description and illustration suggest affinities with Molina’s species. This synonymy is currently open awaiting further analysis.

The status of Solen luzonicus Dunker as junior synonym of E. macha is herein confirmed ( Fig. 3A–B ). The records of Solen luzonicus of authors (non Dunker, 1862), cited from the Indo- Pacific and eastern Pacific ( Bernard et al. 1993; Habe 1964; Liu 2008; Tsuchida & Hayashi 1994) would belong to S. canaliculatus Tchang & Hwang, 1964 (WoRMS 2020). It was G. B. Sowerby II, 1874 (in Reeve & Sowerby 1843-1878) who first synonymized Dunker´s species with E. macha . Sowerby II stated “It is quite impossible to discover any specific difference between the Patagonian and Philippine shells…” (unpaged, see text of Species 12 of Sowerby II, 1874, in Reeve & Sowerby 1843-1878). In this context, it is probable that the registered type locality of Ensis luzonicus Dunker, 1862 (Luzon Island, Philippines) was erroneous. Solen poirieri described by Mabille & Rochebrune (in Rochebrune & Mabille 1889) for Orange Bay, Tierra del Fuego, was mentioned by Carcelles (1944) as young specimens of E. macha . After revising type material from the MNHN, Paris, we confirm this statement ( Fig. 3C–F ).

The specimens identified as E. macha by Ihering (1907a) from the San Sebastian Islands, Brazil, are beyond their currently confirmed geographic range and could belong to Solen (Ensisolen) tehuelchus . Material, labelled as Solen scalprum King, 1832 , from MACN (16684; 12017; 11163; 10230; 10689; 635; 9363; 11667) belong to Solen (E.) tehuelchus . According to Huber (2010), Solen scalprum Gould, 1851 (non King, 1832), is a valid species of Cultellus (Pharidae) from Singapore.

Comparisons: The results exposed by Atkins (1936) related to Ensis species are similar to the morphology observed in E. macha . The fusion of the anterior part of the dorsal edges of the ascending lamellae with the foot were also observed in the South American species. Ensis macha shows food grooves on the ventral edge and between demibranchs ( Fig. 5G ). This species is the only member of the family Pharidae in the southwestern Atlantic. Records of this species from Tubul, Chile, to the north in the Pacific coast of South America belong to a new taxon, currently in process of description (Signorelli et al. in prep.). Compared to other Ensis species , the shell of E. macha reaches 22 cm in length, but can be considerably broader than E. siliqua ( Linnaeus, 1758) ( Cosel 2009) . The free portion of the siphons in E. macha is less prominent than in E. directus ( Conrad, 1843) and E. ensis ( Linnaeus, 1758) ( Bloomer 1905b, 1906) and the posterior end is not curved outwards or inwards as in those two species. Related to the musculature, the anterior adductor is more elongate towards the posterior end but less broad, and the posterior adductor is closer to the pallial sinus than in E. ensis ( Bloomer 1906) . Whereas, compared with E. magnus , E. macha has the posterior adductor less elliptical and the anterior adductor less broad. Bloomer (1906) also observed that the fourth aperture in E. macha is central and longer than in E. ensis in which it is more posteriorly placed, but placed in a similar position as in E. magnus . And the tentacles bordering the siphonal apertures are less numerous in E. macha than in E. ensis ( Bloomer 1906) .

Figures

FIGURE 3. A–B: Ensis luzonicus Dunker, 1862. ZMB 108700, holotype; C–F: Solen poirieri Mabille & Rochebrune, 1889. MNHN-IM 2000-31622, syntypes. Scale bars: A–F = 2 cm.

FIGURE 4. A–H: Ensis macha shell morphology. A–B: outer view, MLP 2702; C–D: inner view, MLP 6829; E: detail of left hinge; F: detail of right hinge; G: dorsal view; H: inner dorsal view. Scale bars: A–D = 2 cm; E–F = 0,5 mm; G–H: 2 cm.

FIGURE 5. A–G: Ensis macha mantle organs. A: right view; B: incurrent and excurrent siphons; C: anterior adductor muscle; D: posterior adductor muscle; E: foot; F: labial palps association with the left demibranch; G: outer right demibranch. Scale bars: A = 2 cm; B, F = 3 mm; C = 1 cm; D–E = 5 mm; G = 2 mm.