Kiel and Taviani—Miocene methane-seep bivalves from Italy
457
Figure 11. Archivesica aharoni new species from Miocene seep deposit in Italy: (1, 2) holotype (MGGC 21909) from Ca’ Pianté, dorsal view, and close-up of hinge of right valve, respectively; (3) paratype (MSF 1048) from Ca’ Pianté, close-up of hinge of left valve; (4) paratype (MGGC 21928) close-up of hinge of right valve; (5) paratype (MGGC 23009) from Verzino, close-up of hinge of left valve.
Table 6. Measurements of Archivesica aharoni new species; H=height, L=length,W=width of two valves.
Locality Specimen
Ca’ Piantè MGGC 21909, holotype Ca’ Piantè MSF 1048 Ca’ Piantè MSF 1055 Ca’ Piantè MSF 1053 Ca’ Piantè MSF 1046 Ca’ Piantè MSF1051
Case Rovereti MZB 23846, paratype Case Rovereti MZB 28075 Verzino MZB 28077 Verzino MZB 28076
L (mm) H (mm) W(mm) 99.0
85.0
54.0 46.0
65 (incomplete) 55.0 81.0 96.0 88.0
51.0 Verzino MGGC 23009, paratype 64 (incomplete) 38.0
115.0 85.0 95.0 90.0
16.0 15.0
36
53.0 21 (single) 51.0
63.0 11 (single) 51.0 54.0
14.0 33
39.5
53.0 19 (single) 21.0
margin, wedge-shaped, tapering anteriorly, 2b short, perpendi- cular to 2a, 4 short, wedge-shaped, nearly perpendicular to ventral shell margin.
Etymology.—For Paul Aharon, Tuscaloosa, Alabama, in recognition of his relevant work on Gulf of Mexico recent cold seeps and ‘Calcari a Lucina’ fossil counterparts.
Materials.—Two specimens from Ca’ Piantè (MSF 1055, 1358) and four shells from Verzino (MGGC 23002).
Remarks.—The two most similar species are the extant Japanese Archivesica soyoae and A. kawamurai. The former differs from A. aharoni n. sp. mainly by having a broader nymph plate and the teeth in the left valve are more elongate (Sasaki et al., 2005). In addition to the left valve teeth of Archivesica kawamurai being more elongate than in A. aharoni n. sp., the teeth of the
right valve are more slender (Sasaki et al., 2005; Amano and Kiel, 2010). The geographically close Phreagena sp. from a ca. 25,000 years old vent field on the Mid-Atlantic Ridge (Lartaud et al., 2010) differs from A. aharoni n. sp. by having the anterior onset of the pallial line in a more anterior position, cardinal tooth 3b in the right valve points posteriorly rather than ventrally as in A. aharoni n. sp., and its escutcheon is much broader. The late Miocene A. shikamai Amano and Kiel, 2010 from Japan differs by generally having straighter and more parallel dorsal and ventral margins.
Archivesica aff. aharoni Kiel and Taviani, herein Figure 12
Description.—Shells up to 94mm long, elongate-veneriform shell with umbo anterior at ~26–35% total shell length; anterior margin either pointed or truncate; ventral margin evenly curved; posterodorsal margin almost straight to slightly convex, transi- tion to posterior margin with clear angulation in specimens with truncate posterior margin, or more rounded in specimens with pointed posterior margin. Beak elevated, blunt, slightly proso- gyrate; external sculpture of rough growth lines only; no lunula or lunular incision. Anterior adductor muscle scar distinct and round, pallial line starting at its posteroventral corner, pallial sinus small, shallow; posterior adductor muscle scar large, round, with anteriorly pointed hook at dorsal margin. Hinge plate high but short; RV with three equally strong cardinal teeth that radiate anteroventrally; LV with three teeth, cardinal 2a wedge-shaped, tapering anteriorly, parallel to anterodorsal margin, 2b and 4 short.
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