Kiel and Taviani—Miocene methane-seep bivalves from Italy
lunula or lunular incision, escutcheon narrow with sharp edges, length at least half of posteroventral margin. Anterior adductor muscle scar distinct, oval, somewhat pointed anteroventrally,most deeply impressed on posterior side, with groove extending toward umbo; anterior pedal retractor scar small, oval, distinct from adductor muscle scar; pallial line starting at posteroventral corner of anterior adductor scar, running oblique toward ventral shell margin in anterior half of shell, paralleltoitafterward, sharply bent upward belowcenter of posterior adductor scar, pallial sinus small, shallow. Hinge plate high but short; RV with three equally strong cardinal teeth that radiate toward ventral margin, cardinals 3a and 3b not connected, subumbonal pit present, nymph plate narrow; LV with three widely radiating teeth, cardinal 2a weak, 2b short, wedge-shaped, not connected to 2a, 4 short, nearly perpendicular to 2a.
Etymology.—For the Apennine Mountains, Italy.
Materials.—All specimens from Castelvecchio; MSF 2121–2132 and several fragmentary specimens at MSF; see Table 7 for measurements.
Remarks.—Archivesica apenninica n. sp. is variable in elonga- tion, but the characteristic broadly arched posterodorsal margin, as well as the nearly equally strong hinge teeth are seen in all available specimens. A similar broadly arched posterodorsal margin is present in the Recent Japanese species A. solidissima (Okutani, Hashimoto, and Fujikura, 1992), A. soyoae (Okutani, 1957), and A. okutanii (Kojima and Ohta, 1997), but these
Table 7. Measurements of Archivesica apenninca new species, all specimens from Castelvecchio; H=height, L=length,W=width of two valves, except when indicated otherwise.
Specimen
MGGC 23001 (holotype) MSF 2123 (paratype) MSF 2127 MSF 2122
MSF 2126 (paratype) MSF 2124
MSF 2125 (paratype) MSF 2121 (paratype) MSF 2129 MSF 2131 MSF 2128
L (mm) H (mm) W(mm) 96
123 122
122 (incompl.) 120 110 109 108 104
103 (incompl.) 85 (incompl.)
62.5 64 67 63 70 71 57
64 61 69 70
19 (RV) 20 (RV) 17 (LV) 17 (LV)
45 (articulated) 24 (LV) 26 (LV) 21 (RV)
50 (articulated) 51 (articulated) 19 (RV)
461
species differ from A. apenninica either by having a concave ventral margin or by having more anteriorly pointing cardinal teeth (Sasaki et al., 2005). The pallial sinus is more pronounced in extant species than in A. apenninica.
Genus Pliocardia Woodring, 1925
Type species.—Anomalocardia bowdeniana Dall, 1903, late Pliocene Bowden Formation, Jamaica, by monotypy.
Remarks.—Pliocardia is currently a dustbin taxon used for small to moderately sized, oval and thick-shelled species with an Archivesica-like hinge dentition. Molecular phylogenetic studies indicate two separate groups among specieswith the general shape of Pliocardia: one includes the species Vesicomya stearnsii, Calyptogena ponderosa, C. cordata,and ‘Pliocardia’ krylovata, the other includes Vesicomya kuroshimana, V. crenulomarginata, and specimens called “cf. venusta” (Kojima et al., 2004; Martin and Goffredi, 2011; Audzijonyte et al., 2012). Several additional extant species for which no molecular data are available are also included in this genus (Krylova and Sahling, 2010), as well as several fossil taxa (Amano and Kiel, 2007, 2012). As it is still unclear to which of those groups (if at all) the type species of Pliocardia belongs. The identity of this genus remains unclear and it is only used in quotation marks for the species reported below.
“Pliocardia” italica new species Figure 15
Type specimens.—Holotype: MGGC 21909 (cast: MSF 1277). Paratype: MSF 1275; all types from the middle Miocene of Ca' Cavalmagra.
Diagnosis.—Large, inflated Pliocardia with strong, protruding, prosogyrate beak, small anterior portion and broadly expanded posterior portion.
Occurrence.—Known only from Ca' Cavalmagra.
Description.—Well-inflated specimens with large, protruding beak in anterior third of shell; anterior part of shell short, somewhat pointed, posterior part broadly expanded; anterior adductor muscle scar in ventral half of shell, broadly oval, onset
Figure 15. “Pliocardia” italica new species from the middle Miocene seep deposits at Ca’ Cavalmagra in northern Italy, holotype (MGGC 21909); (1) exterior of left valve; (2) ventral side; (3) anterior side.
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