Kiel and Taviani—Miocene methane-seep bivalves from Italy
Table 1. Measurements of Bathymodiolus (s.l.) moroniae new species; H=height, L=length, W=width of two valves, except when indicated otherwise.
Locality
Case Rovereti Case Rovereti Case Rovereti Case Rovereti Case Rovereti Case Rovereti Case Rovereti Case Rovereti Verzino Verzino Verzino
Case Rovereti Case Rovereti Case Rovereti
Bivio Castelnuovo Ca' Piantè Ca' Piantè
Abisso ”Mornig” Abisso ”Mornig” Abisso ”Mornig” Abisso ”Mornig” Abisso ”Mornig” Abisso ”Mornig”
Specimen
MZB 21907, holotype MZB 27270, paratype MZB 27218, paratype MZB 27268, paratype MZB 27273, paratype
MZB 27273, specimen on same block MZB 27272 MGGC 21927 MGGC 21923 MGGC 21924 MGGC 21925 MGGC 21920 MGGC 21921 MGGC 21922 MSF 1100
MSF 1360, specimen on same block MSF 1086 MSF 2119 MSF 2120 MSF 1090 MSF 1097 MSF 1094
MSF 1360, paratype
one figured), MSF 1353 (right valve), MSF 1190 (left valve); all types from Le Colline.
Diagnosis.—Small- to medium-sized “Bathymodiolus” with subterminal umbo, broad anterior margin, and arched dorsal margin; maximum inflation just anterior to middle of shell; blunt ridge running from umbo to posteroventral corner.
Occurrence.—Middle Miocene (early Serravallian) seep carbonates at Le Colline in northern Italy.
Description.—Well inflated, moderately sized, arched modioli- form shell with low, subterminal umbo; maximum inflation just anterior of center; anterior margin broad and well rounded, posterodorsal margin broadly arched in large specimens, smaller specimens with distinct posterodorsal corner, ventral margin slightly concave in small specimens, strongly concave in large ones; posterior margin gently rounded; blunt ridge running from umbo to posteroventral corner; surface smooth except for growth increments.
Etymology.—Referring to the Miocene Mediterranean Basin.
Materials.—Three specimens from Le Colline (MSF 2136); see Table 2 for measurements.
Remarks.—Similar in shape is ‘Modiola’ pistacina Sacco, 1904 fromthe Burdigalian of Piedmont (Sacco, 1904, pl. 29, fig. 6a, b; Merlino, 2007, pl. 6, figs.8,9);
the type specimen issmall
(~13mmlong) and has the umbo in amore posterior position and a broader anterior margin than B. miomediterraneus n. sp.
L (mm) 61
41.7 52.0
72 (incomplete) 110 (incomplete) 64.0 39.0 27.6
74 (incomplete) 61 (incomplete) 87 (incomplete) 95
41.2 (incomplete) 11
101.5 (incomplete) 133
93 (incomplete)
85 60 85
82 (incomplete)
‘Modiola’ pistacina may be related to small bathymodiolins such as “Idas” and should be further investigated in the context of whale- and wood-fall communities in the Italian Neogene. The middle Miocene ‘Modiola’ exbrocchii (e.g., the specimen illustrated asModiola brocchii by Hörnes, 1870) and its variation M. exbrocchii var. tauroparva Sacco, 1898, a small species of ~20mm length (Sacco, 1898, pl. 11, figs. 28, 29; Merlino, 2007, pl. 6, fig. 7), have a more elevated umbo and a more distinctive ridge running from the umbo to the posterior-ventral margin than B. miomediterraneus. The new species differs from Bathymodiolus (s.l.) moroniæ n. sp. by having the umbo in a more anterior (subterminal) position. The most similar Recent species are Bathymodiolus mauritanicus von Cosel, 2002, which occurs offWestAfrica and in theGulf of Cadiz (vonCosel, 2002; Génio et al., 2008) and appears to have a broader posteriormargin than B. (s.l.) miomediterraneus n. sp., and the Japanese Bathymodiolus hirtus Okutani, Fujikura, and Sasaki, 2004, which has amore elevated umbo as adult than B.(s.l.) miomediterraneus n. sp. and is broader (less slender) as juvenile (Okutani et al., 2004). A fossil species with a similar subterminal umbo is the presumably Oligocene Bathymodiolus (s.l.) palmarensis from Colombia (Kiel et al., 2010), but it differs from B. (s.l.) miomediterraneus n. sp. by being more elongate and by having almost straight anterior and posterior margins. Bathymodiolus (s.l.) miomediterraneus n. sp. is typically found with articulated valves, in contrast to Bathymodiolus (s.l.) moroniae n. sp. and Samiolus iohannesbaptistae n. gen. n. sp.
Genus Samiolus new genus
Type species.—Samiolus iohannesbaptistae new genus new species, from late Miocene seep deposits in northern Italy.
Figure 2. Bathymodiolus (s.l.) moroniae new species from Miocene seep deposits in Italy: (1, 2) holotype (MGGC 21907) from Case Rovereti, isolated right valve; (3) paratype (MZB 27273) from Case Rovereti, internal mold of large specimen, left valve; (4) paratype (MZB 27270) from Case Rovereti, left valve with preserved shell; (5, 6) paratype (MRSN PU 40607.01) from Deruta, internal mold of articulated specimen; (7, 8) paratype (MGGC 21922) from Case Rovereti, left valve of juvenile specimen showing fine taxodont dentition on posterior side of shell; (9) paratype (MSF 2119) from Abisso “Mornig,” left valve, anterior side with shell remains, posterior side internal mold showing pallial line and adductor muscle scar; (10) paratype (MRSN PU 40607.02) from Deruta, left valve with preserved shell; (11) paratype (MSF 1100) from the Monticino-Limisano – Castelnuovo junction, large right valve with preserved shell.
H (mm) 27.8
21.4 33.0
49 29 20
14.3 37 25 47 42 20
5.4
49.5 52 40
W(mm)
9.3 (single) 8.5 (single)
13 (single) 17 (single)
12 9.5
9.5 (single) 18 (single)
15.5 (single) 10.4
2 (single) 17.5 16 12
447
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