Taxonomic Revision of Living Boring Bivalves Belonging to the Family Pholadidae Lamarck, 1809, (Bivalvia: Myida) from the Southwestern Atlantic

© 2021 Academia Sinica, Taiwan Open Access Taxonomic Revision of Living Boring Bivalves Belonging to the Family Pholadidae Lamarck, 1809, (Bivalvia: Myida) from the Southwestern Atlantic Marina Delfino1,2 and Javier H. Signorelli1,* 1Instituto de Biología de Organismos Marinos (IBIOMAR, CCT CONICET-CENPAT). Bvd. Brown 2915, U9120ACD Puerto Madryn, Chubut, Argentina. E-mail: [email protected] (Delfino) 2Universidad Nacional de la Patagonia San Juan Bosco (UNPSJB), Puerto Madryn, Chubut, Argentina. *Correspondence: E-mail: [email protected] (Signorelli) Received 1 October 2020 / Accepted 7 March 2021 / Published 24 June 2021 Communicated by James D. Reimer Boring bivalves of the family Pholadidae Lamarck, 1809 living in Argentinean and Uruguayan waters are herein revised. The literature research revealed twelve nominal species of Pholadidae mentioned as living in the study area. Type material of all nominal taxa were examined when it was possible. Additional specimens from field works and malacological collections were studied, illustrated and re-described. Details of type localities, repositories, and distribution range are provided for each valid taxa. This work revealed the presence of five native and one introduced species belonging to Pholadidae in Argentinean and Uruguayan waters. Barnea (Anchomasa) lamellosa, Cyrtopleura (Scobinopholas) lanceolata, Pholas (Thovana) campechiensis and Martesia fragilis belonging to the Argentine biogeographical province; Netastoma darwinii from Magellan province; and Barnea (Anchomasa) truncata introduced in the Bahía Blanca estuary. Finally, morphological comparison with congeneric species distributed in American seas are provided. Key words: Pholas, Barnea, Martesia, Cyrtopleura, Nettastoma, Argentina, Taxonomy, Boring bivalves. BACKGROUND The classification of the superfamily Pholadoidea Lamarck, 1809 has been modified over the years. Several authors recognized the families Pholadidae Lamarck, 1809 and Teredinidae Rafinesque, 1815 (Turner 1954 1955 1969 2002; Monari 2009; Bieler et al. 2010; Huber 2010). Within Pholadidae the subfamilies Pholadinae, Martesiinae, Jouannetiinae and Xylophagainae were historically grouped (Hoagland and Turner 1981; Bernard 1983; Harvey 1996; Turner 2002; Mikkelsen and Bieler 2007; Bieler et al. 2010; Huber 2010). However, Xylophagaidae Purchon, 1941 was considered as separate from the Pholadoidean family (Harvey 1996; Haga and Kase 2008 2013; Coan and Valentich-Scott 2012; Paredes et al. 2016; Coan et al. 2017). Some works elevated Jouannetiidaea to the family level (Coan and Valentich-Scott 2012; ValentichScott et al. 2020). In this work the classification of Bieler et al. (2010) is followed. The members of the family Pholadidae are specialized to bore different types of substrates that affect the morphology of the shell and soft parts (Turner 1969). In general terms, they are characterized by an aragonitic fragile, ovate to elongate and widely gaping shell; dorso-anterior area with umbonal reflection; external surface very sculptured with reticulate or imbricated spines and separated by a radial sulcus to Citation: Delfino M, Signorelli JH. 2021. Taxonomic revision of living boring bivalves belonging to the family Pholadidae Lamarck, 1809, (Bivalvia: Myida) from the southwestern Atlantic. Zool Stud 60:28. doi:10.6620/ZS.2021.60-28. Zoological Studies 60:28 (2021) doi:10.6620/ZS.2021.60-28 1 © 2021 Academia Sinica, Taiwan define distinct zones. The hinge is simple, without teeth and external ligament mainly absent. Some species are trimyarian with the ventral adductor muscle; siphons totally fused, usually covered by a periostracum; pedal muscle subject by the apophysis; foot truncate with discoid extremity; valves with accessory plates along the dorsal margin called protoplax, mesoplax and metaplax; anterior pedal gape closed by a callum in adults. Five species belonging to the family Pholadidae were cited as living in the southwestern Atlantic Ocean from Uruguay to Argentina (Carcelles 1944; Carcelles and Williamson 1951; Castellanos 1970; Rios 1994 2009; Scarabino 2003; Scarabino et al. 2006 2016; Zelaya 2016). They are Barnea lamellosa (d'Orbigy, 1841 in 1834–1847), Cyrtopleura lanceolata (d'Orbigy, 1841 in 1834–1847), Pholas campechiensis Gmelin, 1791, Martesia fragilis Verril and Bush 1898 and Netastoma darwinii (G. B. Sowerby II, 1849). Nevertheless, twelve nominal species were mentioned in the literature related to the study area. During an ongoing revision of different groups of boring bivalves, it became necessary to revise the taxonomy of the species belonging to the family Pholadidae living in the Argentinean and Uruguayan waters. MATERIALS AND METHODS A total of 260 lots were examined from malacological collections. In addition, field works on several localities of Argentine Patagonian coast were carried out. However, only specimens of Barnea (Anchomasa) lamellosa and Netastoma darwini with soft parts were found. The sampled specimens were removed mechanically from the substrate with a geologist hammer. Digital pictures were taken with a Nikon D5000 with a 60 mm Nikkor micro lens. All specimens were cleaned and studied under stereoscopic microscope. Diagnostic characters and mantle cavity organs, when it was possible, were revised and redescribed. All dissections were done after Magnesium chloride relaxing method. The type locality and recording sites of revised species are illustrated in the figure 1. Type material and additional specimens studied in this work are deposited in the following institutions: ANSP, Academy of Natural Sciences of Philadelphia; IBIOMAR - CNP-INV, Instituto de Biología de Organismos Marinos; LSL, Linnean Society of London; MACN, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; MLP, Museo de La Plata; NHMUK, Natural History Museum, London; USNM, United States National Museum. The following abbreviations are used: aam: anterior adductor muscle; ap: apophysis; cm: collecting mass; es: excurrent siphon; f: foot; fg: food groove; ild: inner left demibranch; illp: inner left labial palp; ird: inner right demibranch; irlp: inner right labial palp; is: incurrent siphon; llp: left labial palp; old: outer left demibranch; ollp: outer left labial palp; ord: outer right demibranch; orlp: outer right labial palp; pam: posterior adductor muscle; pg: pedal gape; pt: Protoplax; rlp: right labial palp; s: siphons; ur: umbonal reflection; vam: ventral adductor muscle; vm: visceral mass; z1: zone 1; z2: zone 2; z3: zone 3. RESULTS Family Pholadidae Lamarck, 1809 Subfamily Pholadinae Lamarck, 1809 Genus Barnea Risso, 1826 (ex Leach MS) [= Barnia Gray, 1840: 150 (error pro Barnea); Holopholas Fischer, 1887 in 1880–1887: 1133 (objective)]. Type species: Barnea spinosa Risso, 1826 (= Pholas candida Linnaeus, 1758), by monotypy. Distribution: Cosmopolite. Remarks: Barnea includes sixteen valid species widely distributed (Monari 2009; Huber 2010). It differs from other genera within Pholadinae by having only a single lanceolate protoplax. In addition to that, the umbonal reflection is not septate, as in Pholas, and the valves are not divided by an umbonal-ventral sulcus as in Zirfaea (Kennedy 1974). Fischer (1887) introduced Holopholas as a subgenus of Pholas and included Barnea as a subsection of Holopholas, for this reason Barnea and Holopholas are objective synonyms. Barnea has two subgenera: Barnea s. s. and Anchomasa. Barnea s. s. does not occur in the southwestern Atlantic Ocean (Kennedy 1974; Huber 2010). Species included into the subgenus Anchomasa have shells anteriorly beaked, wide posterior end and large pedal gape (Kennedy 1974; Huber 2010). Subgenus Anchomasa Leach, 1852 Type species: Anchomasa pennantiana Leach, 1852 (= Pholas parva Pennant, 1777), by monotypy. Distribution: Widely distributed, south and west coast of Africa, Japan and Indian seas, South Australia and New Zealand, Europe, west and east coast of America. Remarks: Currently the subgenus Anchomasa includes eleven valid species (Huber, 2010). They are: Barnea (Anchomasa) alfredensis (Bartsch, 1915), B. (A.) davidi (Deshayes, 1874 [1873]), B. (A.) fragilis (G. page 2 of 20Zoological Studies 60:28 (2021) © 2021 Academia Sinica, Taiwan B. Sowerby II, 1849), B. (A.) ghanaensis Huber, 2018 (in Cosel and Gofas, 2018), B. (A.) lamellosa (d'Orbigy, 1841 in 1834–1847), B. (A.) manilensis (Philippi, 1847 [1847-1848]), B. (A.) obturamentum (C. Hedley 1893), B. (A.) parva (T. Pennant 1777), B. (A.) similis (Gray in Yate 1835), B. (A.) subtruncata (G. B. Sowerby I 1834), B. (A.) truncata (T. Say 1822). Future genetic works will clarify the sub-generic status of the mentioned species. Barnea (Anchomasa) lamellosa (d'Orbigy, 1841 in 1834–1847) (Figs. 2A–C, 3) Pholas lamellosa – d'Orbigny 1841 in 1834–1847: 498, pl. 77, figs. 20, 21; Dall 1908: 289. Barnea lamellosa – Ihering 1907: 329; Castellanos 1970: 258, pl. 26, figs. 1–2; Figueiras and Sicardi 1970: 412, pl. 5, fig. 80; Scarabino 1977: 215; Bernard 1983: 60; Scarabino 2003: 242; Dias Passos and Magalhães 2011: 148; Scarabino et al. 2016: 10. Barnea (Anchomasa) subtruncata lamellosa – Lamy 1925: 82; Carcelles 1944: 295, pl. 14, figs. 108–109; Carcelles 1950: 82. Barnea subtruncata lamellosa – Barattini 1951: 256; Barattini and Ureta 1961: 184. Barnea (Anchomasa) lamellosa – Turner 1954: 25, pl. 8 and 10; Figueiras 1962: 64; Olazarri 1962: 51; Klappenbach 1967: 164; Fig. 1. Map of the study area showing the type locality and the recording sites of the species herein revised. N page 3 of 20Zoological Studies 60:28 (2021) © 2021 Academia Sinica, Taiwan Rios 2009: 591, fig. 1630; Huber 2010: 474. Type material: NHMUK 1854.12.4.655, two syntypes, an articulated specimen and a single valve. Type locality: “Patagonie, au sud du Rio Negro”, Rio Negro Province, Argentina. Description: Shell: fragile, pellucid, equivalve, moderately elongated, inequilateral; shell length up to 50 mm; anterior end pointed, forward projected; posterior end rounded (Fig. 3A–B); umbos prosogyrate, subcentral; umbonal reflection totally free, well developed on the anterior side of the umbo; apophysis prominent, long, narrow, curved and ventrally projected inside each valve, dorso-posterior margin curved; ventral margin almost straight, slightly rounded; external surface with concentric sculpture defined by spines, more conspicuous on the anterior side of the shell (Fig. 3A); internal surface white; hinge plate rudimentary; pallial sinus broad and deep; adductor muscle scars moderately marked (Fig. 3B). Dorso-anterior area with a calcareous protoplax, strongly keeled, rhomboid and narrow (Fig. 3E); valves not completely closed over the ventral edge; pedal gape rounded. Mantle cavity organs: siphons totally fused, very elongated, twice shell length, with mud and sand particles attached to the external surface (Fig. 3C, F– G); incurrent siphon wider than excurrent, with a ring of white and single tentacles, equal in size and length; space between tentacles brownish; excurrent siphon without tentacles; two demibranchs at each sides of the body, equal in length, food groove present over the ventral edge of inner and outer demibranch (Fig. 3H– I); labial palps trigonal with the outer surface smooth and inner plicate (Fig. 3J); visceral mass white; on the posterior area with a collecting membrane, trigonal, inflate, well developed; foot large, tubular; pedal gape disc-like; dimyarian, adductor muscles lenticular. Material examined: Uruguay ─ Departamento de Rocha (MACN 14790); Argentina ─ Santa Clara del Mar (MLP 7781), Mar del Plata (MACN 10745, MACN 11991), Miramar (MACN 15636), Monte Hermoso (MACN 6619, MLP 7780), Bahía Blanca (MACN 38385), Punta Alta (MACN 11171), San Blas Bay (MACN 20213), Rio Negro mouth (MLP 2510), San José gulf, Punta Tehuelche (CNP-INV 2910, 2911, 2912), Puerto San Julián (CNP-INV 2908, 2909). Distribution: Santa Catarina, Brazil to the Malvinas/Falkland Islands (Rios 2009). In this work specimens from Rocha, Uruguay, to Puerto San Julián in Santa Cruz province were revised. Remarks: Barnea lamellosa has been recorded boring horizontal consolidated mud substrates in the intertidal zone, usually covered with a layer of sand. The sampled specimens were found in a very low density. Although Tryon (1868) and Carcelles (1944) mentioned Barnea (Anchomasa) lamellosa (d'Orbigy, 1841 in 1834–1847) as synonym of B. (Anchomasa) subtruncata, type material examination confirmed that both species are valid. Barnea subtruncata (Fig. 2G– J) is distributed along the Pacific coasts of America, from USA to northern Chile, whereas B. lamellosa (Fig. 2A–C) inhabits the coasts of Argentina and Uruguay (Coan and Valentich-Scott 2012; Scarabino et al. 2016; Zelaya 2016). No additional synonym of B. lamellosa were found in the literature. Barnea lamellosa differs from the eastern Pacific B. subtruncata in being shorter, with a less elongated posterior end and by having a shallowest pallial sinus. Kellog (1915) described the collecting membrane for B. costata and B. subtruncata (as B. pacifica). The morphology of this character has taxonomic value. Atkins (1937) and Purchon (1955) described this membrane in other Pholadidae highlighting size differences between species. In B. lamellosa the collecting membrane is wider than in B. costata and B. subtruncata (Fig. 3H). The collecting membrane of the visceral mass, is posteriorly oriented and projected to the mantle cavity. It is a retractile and ciliated organ related to cleaning functions that prevent the entrance of sediment into the mantle cavity at low tide (Kellog 1915). Barnea (Anchomasa) truncata (Say, 1822) (Fig. 2D–F) Synonyms [for complete list see Turner, 1954; here, only the selected combinations found in the most important literature are listed] Pholas truncata – Say 1822: 321; G.B. Sowerby II 1849: 488, pl. 104, figs. 29–30. Pholas (Cyrtopleura) truncata – Tryon 1862: 202; Lamy 1925: 87. Barnea truncata – Dall 1889: 72, 1898: 816; Perry 1940: 88; Nicklès 1950: 232, fig. 454; Abbott 1954: 461; Moore 1961: 16; Barnard 1964: 565; Kilburn and Rippey 1982: 203; Kensley and Pether 1986: 209, fig. 14; Mikkelsen and Bieler 2004: 609; Ardovini and Cossignani 2004: 54, 292; Turgeon et al. 2009: 736; Velásquez et al. 2017: 254, figs. 12–13. Barnea (Anchomasa) truncata – Turner 1954: 27, pl. 8, figs. 11–13; Huber 2010: 474; Cosel and Gofas 2019: 982–983. Type locality: “southern coast of the United States”, it was restricted to Charleston, South Carolina by Turner (1954). Type material: Types was not found in ANSP cabinets. The specimen was deposited at the ANSP by Say itself. A probable syntype (ANSP 50775) was illustrated by Turner (1954). Description: Shell: medium to large, length up to 5 cm, thin, elongated, gaped at both ends, beaked anteriorly; external surface with radial ribs declining gradually, strong on the anterior slope, but almost smooth on the posterior side of the shell; dorsal margin page 4 of 20Zoological Studies 60:28 (2021) © 2021 Academia Sinica, Taiwan slightly curved; umbonal reflection almost in touch with the umbos but anteriorly free; internally white, hinge plate without teeth, but with an apophysis, long, narrow, curved and ventrally projected inside each valve; dorsoanterior area covered by a thin protoplax, with parallel sides, not attached to the anterior adductor muscle. Fig. 2. A−C, Barnea (Anchomasa) lamellosa (d'Orbigy, 1841 in 1834–1847), NHMUK 1854.12.4.655, syntypes. D−F, Barnea (Anchomasa) truncata (Say, 1822), MACN 38385 from Bahía Blanca. G−J, Barnea (Anchomasa) subtruncata (G. B. Sowerby I, 1834, in 1821−1834), material collected by d'Orbigny in Payta, Perú, NHMUK 1854.12.4.656. The specimens of B. (A.) lamellosa and B. (A.) subtruncata with the apophysis broken. Scale bar = 1 cm. page 5 of 20 Zoological Studies 60:28 (2021) © 2021 Academia Sinica, Taiwan Fig. 3. Barnea (Anchomasa) lamellosa. A, external view right valve. B, internal view right valve. C, external view of living specimen. D, anterior view showing pedal gape and foot. E, detail of calcareous protoplax. F−G, detail of siphons. H, general aspect of mantle cavity organs. I, detail of food groove over the distal edge of the outer demibranch. J, detail of left labial palps and apophysis. Scale bars: A−B, D−E, H−J = 5 mm; C = 1 cm; F−G: 2.5 mm. page 6 of 20Zoological Studies 60:28 (2021) © 2021 Academia Sinica, Taiwan Mantle cavity organs: Siphons totally fused, covered by the periostracum, extended almost ten times shell length, papillose tentacles surrounding both siphons; incurrent siphon with a row of single tentacles, excurrent siphon without tentacles; brownish pigmentation between tentacles, extended along the inner wall of the siphons; foot white and oval. Material examined: United States of America ─ South Carolina (ANSP 50775); Argentina ─ Bahia Blanca (MACN 38385). Distribution: Northwestern Atlantic Ocean, from Canada to Florida (Bousfield 1960; Hebda 2011; Mikkelsen and Bieler 2007; Turgeon et al. 2009), Brazilian coast (Rios 2009), Senegal to Congo (Barnard 1964; Cosel and Gofas 2019), Bahía Blanca, Argentina (Fiori et al. 2012, reported as introduced). Remarks: Barnea truncata was widely found boring in wood, clay, and soft rocks (Barnard 1964; Rios 2009; Díaz Merlano and Puyana Hegedus 1994). No synonyms of this species were found in the literature. It was recently reported as introduced in Bahía Blanca (Fiori et al. 2012; Schwindt et al. 2020). Barnea (A.) truncata differs from B. (A) lamellosa in having a more anteriorly placed umbo, a posterior end more truncate and anterior margin slightly pronounced (Fiori et al. 2012). This species was widely reported from eastern and western Atlantic Ocean. Genetic studies on specimens of Canadian (Bousfield 1960; Hebda 2011; Mikkelsen and Bieler 2007; Turgeon et al. 2009; Turner 1954), African (Barnard 1964; Cosel and Gofas 2019) and Argentine waters (Fiori et al. 2012; Schwindt et al. 2020) will clarify this wide distribution range. Genus Cyrtopleura Tryon, 1862 [= Leuconyx H. Adams and A. Adams, 1863 (name rejected by Turner (1969) as a forgotten name (nomen oblitum) because it was not used as a valid name for 50 years (ICZN 1999, Article 23b)]. Type species: Pholas cruciger G.B. Sowerby I, 1834 by subsequent designation (Stoliczka 1870, 1871). Distribution: Atlantic coast of North America from Massachusetts to Gulf of Mexico, South America from Venezuela to Argentina and Pacific coast of Central America from Panama to Ecuador. Remarks: Cyrtopleura currently includes two subgenera, Cyrtopleura s. s. and Scobinopholas Grant and Gale, 1931, and three living species. The type species Cyrtopleura (C.) crucigera (G. B. Sowerby I, 1834) from the Pacific coast of Central America and northern South America; Cyrtopleura (Scobinopholas) costata (Linnaeus, 1758) and C. (S.) lanceolata (d'Orbigy, 1841 in 1834–1847) (Huber 2010; Coan and Valentich-Scott 2012). Cyrtopleura differs from the genus Pholas in the simple umbonal reflection, not septated, and from Barnea in shell outline, anterior end more rounded and umbonal reflection more developed. Scobinopholas differs from Cyrtopleura s. s. in the rounded anterior end, narrow pedal gape and more conspicuous sculpture. Subgenus Scobinopholas Grant and Gale, 1931 Type species: Pholas costatus Linnaeus, 1758, by original designation. Distribution: East coast of America. Remarks: Scobinopholas currently includes two valid species. Cyrtopleura (Scobinopholas) costata (Linnaeus 1758) and C. (S.) lanceolata (d'Orbigy, 1841 in 1834–1847). The former distributed along the east coast of North and Central America, and the latter living along the southeastern coast of South America. The species included into this subgenus are characterized by a lanceolate protoplax. Cyrtopleura (Scobinopholas) lanceolata (d'Orbigy, 1841 in 1834–1847) (Fig. 4) Pholas lanceolata d'Orbigy, 1841 in 1834–1847, 1841: 497, pl. 77, figs. 18–19. Barnea lanceolata – Tryon 1862: 208; Ihering 1907: 329; Lamy 1925: 43; Carcelles 1944: 295, pl. 16, fig. 110; Barattini 1951: 256; Barattini and Ureta 1961: 184. Barnea (Scobinopholas) lanceolata – Lange de Morretes 1949: 49; Gofferjé 1950: 279. Cyrtopleura (Scobinopholas) lanceolata – Lange de Morretes 1949: 49; Goffergé 1950: 279; Turner 1954: 39–41, pl. 19, figs. 1–3; Olazarri 1962: 51; Figueiras 1962: 64; Rios 1966: 36; Klappenbach 1967: 165; Huber 2010: 475. Cyrtopleura lanceolata – Turner 1954: 39–41, pl. 19, figs. 1–3; Castellanos 1970: 257; Scarabino 1977: 215; Hoagland and Turner 1981: 130; Scarabino 2003: 242; Scarabino et al. 2006: 396, 2016: 7; Rios 2009: 592, fig. 1633; Dias Passos and Magalhães 2011: 148; Zelaya 2016: 254. Type locality: Ensenada de Ros, Rio Negro province, Argentina. Type material: NHMUK 1854.12.4.654, paralectotypes, 3 specimens; MNHN-IM, unnumbered, probable lectotypes, 4 valves (Fig. 4A–K). Description: Shell: lanceolate, fragile, elongated, equivalve, inequilateral, length up to 70 mm, both ends rounded but with the anterior end slightly angled (Fig. 4A–D); umbos well developed sub central but near the anterior third of the shell; umbonal reflections separated from the umbos (Fig. 4A, C); pedal gape narrow and elongated; external surface with a weak radial sculpture, usually absent on the posterior slope in adults, in juvenile specimens radial sculpture observed over the page 7 of 20Zoological Studies 60:28 (2021) © 2021 Academia Sinica, Taiwan entire length; concentric sculpture well developed (Fig. 4A, C, E, G); internal surface white; pallial sinus deep and broad, about 60% of shell length (Fig. 4B, D, F); pallial line and adductor muscle scar well marked; apophysis short but broad, fragile and flattened at the distal end (Fig. 4N); protoplax T-shaped, thin, chitinous, slightly downward curved at its posterior area, closely attached to the muscles; mesoplax calcareous, transverse, composed by two parts, the anterior part inserted into the socket of the umbonal reflection; periostracum yellowish and deciduous. Mantle cavity organs (Based on Turner, 1954 and museum material): siphons totally fused, protected by a light-brown, papillose, chitinous cover; incurrent siphon with a row of single tentacles surrounding the aperture; excurrent siphon without tentacles; pedal gape and foot elliptical in outline. Material examined: Uruguay ─ Punta del Este (MLP 8448, 8449); Argentina ─ Punta Médanos (MLP 16084, 16900), Ostende (MACN 20096), Villa Gesell (MACN 5377), Mar Chiquita (MACN 26529, 29384), Santa Clara del Mar (MLP 7781-2), Mar del Plata (MACN 9361-39, 10234, 10746, 11990), Chapadmalal (MACN 26246), Miramar (MACN 1888, 2329, 2387, 15635, MLP 1443), Puerto Quequén (MLP 2311, 12037), Monte Hermoso (MACN 1421, 1885, 661914, 9210-13, 11169, 14818), Arroyo Chocorí (MACN 19950), Puerto Belgrano (MACN 11168), Bahía Blanca (MACN 4497), Arroyo Parejas (MACN 11167), Caleta Brightman (MACN-INV 16143), Río Colorado (MLP 1386), Villarino (MLP 40815), San Blas bay (MACN 20212), Río Negro mouth (MACN 20547, MLP 1886, 2709, 4894). Distribution: From Sao Paulo state, Brazil to San Matías gulf, Argentina (Turner 1954; Ruhland and Saalfeld 1967; Rios 1994 2009; Scarabino 1977). In this work, specimens from Punta del Este, Uruguay, to Rio Negro mouth were studied. In addition, this taxa had been reported to quaternary deposits of Puerto Belgrano and Mar del Plata (Figueiras 1962). Remarks: Cyrtopleura (Scobinopholas) lanceolata has been reported from calcareous rocks and soft substrates (Rios 1966). No synonyms of this taxa were found in the literature. Although several authors included this species in other genera, such as Pholas and Barnea, the morphology of its shell places it within the genus Cyrtopleura and the subgenus Scobinopholas. Cyrtopleura (S.) lanceolata differ from C. crucigera in showing a more rounded anterior end, lanceolate shell outline, much weaker sculpture and mesoplax in two parts, and from C. (S.) costata by its weak radial sculpture, not observed on the posterior slope, flat apophysis, longer anterior slope and mesoplax in two parts. Genus Pholas Linnaeus, 1758 [= Hypogaea Poli, 1791: 29, objective (partim); Hypogaeoderma Poli, 1795: 251, 257, objective, type species: Pholas dactylus Linnaeus, 1758, by subsequent designation (Turner, 1954); Phloas Turton, 1802: 172 (error pro Pholas); Pholadiarius Duméril, 1806: 310, unnecessary emendation of Pholas Linnaeus; Pholax Renier, 1807: vii (error pro Pholas); Pholadites Schlotheim, 1813: 105, invalid, ICZN 1999, art. 20; Pholalites Schläpfer, 1821: 278 (error pro Pholaldites); Xylotrya Menke, 1830: 121, objective, type species: Pholas dactylus Linnaeus, 1758, by subsequent designation (Clench and Turner, 1946); Dactylina Gray, 1847, type species: Pholas dactylus Linnaeus, 1758, by original designation; Pholadarius Herrmannsen, 1852: 105 (error pro Pholadiarius); Pholalithes Paetel, 1875: 160 (error pro Pholalites); Pragmopholas Fischer, 1887: 1133, type species: Pholas dactylus Linnaeus, 1758, by by subsequent designation (Turner, 1954)]. Type species: Pholas dactylus Linnaeus, 1758, by subsequent designation (Children 1822). Distribution: Eastern and Western Atlantic, Southeastern Pacific, China Seas. Remarks: The genera Pholadites, Dactylina, Xylotrya and Pragmopholas are objective synonyms of Pholas due to their type species is Pholas dactylus. The genus level names Hypogaea, Hypogaeoderma, Phloas and Pholadarius are considered invalid names. Five valid species are currently included into the genus Pholas (Bernard et al. 1993; Huber 2010; Coan and Valentich-Scott 2012; Cosel and Gofas 2018). Pholas dactylus Linnaeus, 1758 from Northeastern Atlantic and P. orientalis Gmelin, 1791 from China Seas belong to Pholas s. s., whereas the other three species are included in the subgenus Thovana Gray, 1847. Subgenus Thovana Gray, 1847 (ex Leach MS) Type species: Pholas oblongata Say, 1822 (= Pholas campechiensis Gmelin, 1791), by monotypy. Distribution: Western Atlantic. Remarks: This subgenus includes Pholas chiloensis Molina, 1782 from southeastern Pacific; P. bissauensis Cosel and Haga, in Cosel and Gofas, 2018 from West Africa and P. campechiensis Gmelin, 1791 from western Atlantic. Thovana differs from Pholas s. s. by having a more rounded anterior end and nuclei of the two halves of the protoplax more anterocentrally located (Coan and Valentich-Scott 2012). Pholas (Thovana) campechiensis Gmelin, 1791 (Fig. 5) Pholas campechiensis – Gmelin, 1791: 3216; Hanley 1842–1856: 6, pl. 9, fig. 44; Abbott 1954: 461; Díaz Merlano and Puyana Hegedus 1994: 101; Scarabino 2003: 242; Scarabino et al. 2006: 396, 2016: 7; Turgeon et al. 2009: 737; Dias Passos and page 8 of 20Zoological Studies 60:28 (2021) © 2021 Academia Sinica, Taiwan Magalhães 2011: 148; Capelo et al. 2014: 34; Velásquez et al. 2017: 254; De Vasconcellos et al. 2018: 52. Pholas oblongata – Say, 1822: 320; Hanley 1842–1856: 5; De Kay 1843: 248; Dall 1898: 815. Pholas candeana – d'Orbigy, 1847 in 1834–1847: 215, pl. 25, figs. 18–19; Dall 1898: 815. Thovana oblongata – Gray 1847: 187. Dactylina campechensis – Adams and Adams 1856 in 1853–1856: 326; Fischer 1858: 49; Carpenter 1864: 635. Dactylina candeana – Chenu 1862 in 1859–1862: 4, fig. 12. Fig. 4. Cyrtopleura lanceolata. A−H, probable lectotypes, MNHN-IM unnumbered. I−N, examined material, MACN 9361-39. Scale bars: A−M = 1 cm; N = 1 cm. page 9 of 20Zoological Studies 60:28 (2021) © 2021 Academia Sinica, Taiwan M. cuneiformis. In addition, Martesia fragilis can be distinguished from M. striata by the thinnest umbonal reflection, most elongated anterior adductor muscle, longest anterior part of the shell, lanceolate hypoplax and largest metaplax (Srinivasan 1959). DISCUSSION The presence of six valid species belonging to the family Pholadidae living in Argentina and Uruguay were confirmed in this study. In a global context 76 valid species are recognized as valid. However, the biodiversity of this group along the southern tip of South America is relatively low. Rios (2009) reported the same genera, but three additional pholadids from Brazil. A similar scenario is observed in tropical East America where the same genera plus Lignopholas in which each species was reported once (Mikkelsen and Bieler 2007; Huber 2010). In European waters five genera (Pholas, Barnea, Martesia, Pholadidea and Zirfaea) and seven valid species were mentioned in the literature (Poppe and Gotto 1993; Gofas et al. 2001; Holmes et al. 2015), and along the Atlantic coast of Africa this group is represented by seven genera (Barnea, Jouannetia, Martesia, Parapholas, Pholas, Pholadidea and Talona) and thirteen taxa (Huber 2010; Cosel and Gofas 2019). Nevertheless, a greater biodiversity of Pholadidae is observed along the Pacific Ocean. In this way, six genera (Barnea, Chaceia, Netastoma, Parapholas, Penitella and Zirfaea) and twelve species were reported in the literature from western North America (Coan et al. 2000). And ten genera (Barnea, Cyrtopleura, Diplothyra, Jouannetia, Martesia, Parapholas, Penitella, Pholadidea, Pholas, and Zirfaea) and seventeen taxa were mentioned from Tropical West America (Coan and ValentichScott 2012). Finally, from the Indo-Pacific region ten genera (Pholas, Aspidopholas, Barnea, Jouannetia, Lignopholas, Martesia, Nipponopholas, Parapholas, Penitella and Pholadidea) and twenty four species were mentioned (Bernard et al. 1993; Huber 2010; Sanpanich 2011). And from southern Australian and New Zealand waters seven genera (Pholas, Aspidopholas, Barnea, Martesia and Jouannetia) and fourteen species from are recognized as valid in the literature (Lamprell and Healy 1998; Huber 2010). In general term, the generic biodiversity of the group is similar along the different regions, being the Tropical West America and the Indo Pacific the most diverse in number of genera and species. This first taxonomic approach focused on living Pholadidae from Argentinean and Uruguayan waters and makes up the nomenclatorial basis for future works. CONCLUSIONS The systematic arrangement of valid species herein confirmed have been modified during the years (Carcelles 1944; Carcelles and Williamson 1951; Castellanos 1970; Rios 1994 2009; Scarabino 2003; Scarabino et al. 2006 2016; Zelaya 2016). Five of the six valid species were originally described as Pholas. Only Martesia fragilis was described in a different genus. This work presents valid species by revising type material of all nominal species. Netastoma darwinii and Pholas (T.) campechensis, type species of its genus and subgenus respectively, are generically stable. Nevertheless, genetic studies of this family will clarify the generic placement of other revised species and the existence of new generic entities. In a biogeographical context, Pholas (Thovana) campechiensis, Barnea (Anchomasa) lamellosa and Cyrtopleura (Scobinopholas) lanceolata belong to the Argentine province, distributed from Brazil to Uruguay and northern Argentina. Martesia fragilis is an ocean traveler widely reported from different regions. Netastoma darwinii is the only Jouannetiinae species present in the study area that extends its distribution to Rio Grande do Sul. The sixth valid species herein confirmed is Barnea (Anchomasa) truncata. In our opinion, the identity of Canadian, west African and Argentinean records of this species must be genetically tested. However, the observed characters of the specimens reported by Fiori et al. (2012) as introduced in the Bahía Blanca coincide with those observed in specimens of B. truncata from north western Atlantic (MACN 38385, Fig. 2D–F). Acknowledgments: Special thanks to Alejandro Tablado and Mariela Romanelli (MACN), to Gustavo Darrigran and Cristina Damborenea (MLP), to Gary Rosenberg and Paul Callomon (ANSP), to Andreia Salvador and Tom White (NHMUK and LSL) and to Ellen Strong and John Pfeiffer (USNM) for their assistance in the revision of type material and additional examined specimens. We are grateful to the Secretaría de Ciencia, Tecnología e innovación productiva de la Provincia de Chubut. This is the contribution #146 of the LARBIM. Authors’ contributions: JHS and MD wrote the manuscript, sampled the specimens, analyze the types and edited the illustrations. MD separated the specimens and examined the museum collections. 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