Kiel and Taviani—Miocene methane-seep bivalves from Italy
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interior; shell composed of a calcitic fibrous prismatic outer layer and a nacreous inner layer.
Etymology.—To honor Maria Antonietta Moroni, for her seminal work on the ‘Calcari a Lucina’ fauna.
Figure 1. Maps showing the fossil localities discussed in the text. Left panel, general map of Italy showing all localities: 1=Abisso “Mornig”,2=Ca’ Carnè, 3=Ca’ Cavalmagra, 4=Monticino-Limisano – Castelnuovo junction, 5=Ca’ Fornace, 6=Ca’ Pianté, 7=Case Rovereti, 8=Castelvecchio, 9=Deruta, 10=Le Colline, 11= Marmorito, 12=Montepetra, 13=Sasso delle Streghe, 14=Verzino.
are settled (Gustafson et al., 1998). Morphologically, the two clades can be distinguished based on muscle-scar pattern (Gustafson et al., 1998), which, unfortunately, is not preserved in any of the fossils reported here from northern Italy. Therefore, we refer to them as Bathymodiolus (sensu lato).
Bathymodiolus (s.l.) moroniae new species Figure 2
1966 Modiolus (Modiolus) exbrocchii exbrocchii Sacco; Moroni, p. 78, pl. 5, fig. 2, pl. 6, fig. 4.
1996 Bathymodiolus exbrocchii Sacco; Taviani, fig. 2a, 4c. 2001 Modiolinid Taviani, fig. 20.7a.
2011 “Bathymodiolus” cf. exbrocchii (Sacco, 1898); Taviani, fig. 3c.
Type specimens.—Holotype: MGGC 21907, single right valve from Case Rovereti. Paratypes: seven specimens from Case Rovereti: MZB 27218, 27268, 27270, 27272, 27273; MGGC 21921, 21922; one from Monticino-Limisano – Castelnuovo junction: MSF 1100; one from Ca’ Piantè (MSF 2135, on same large block asMSF1360); one fromAbisso “Mornig” (MSF 2119).
Diagnosis.—Medium- to large-sized “Bathymodiolus” with blunt, elevated umbo at anterior 10% of total shell length; dorsal and ventral margins nearly straight, posterodorsal corner at posterior third of shell; maximum inflation just anterior to anterior third of shell.
Occurrence.—Late Miocene seep carbonates in Italy.
Description.—Moderately inflated modioliform shell, maximum inflation at ~27% of total shell length; blunt, elevated umbo at anterior 10% of total shell length, anterior margin narrow, convex; ventral margin straight, slightly concave in large specimens; dorsal margin straight to very slightly curved; posterodorsal corner at posterior third of shell; surface smooth except for growth incre- ments; hinge area in juvenile specimens with row of taxodont teeth below the ligament attachment line, smooth in adults; pallial line distant from shell margin, numerous mantle muscle scars toward
Materials.—Forty-four valves (including MZB 27064, 27271, 27278, 27281) from Case Rovereti; three specimens from Verzino (MGGC 21923, 21924, 21925); one from Deruta (MGGC 21926); seven articulated shells from Deruta (MRSN, under cf. Bathymodiolus exbrocchii, PU 40607); one articulated specimen from Verzino MGGC 21927; three articulated shells (MSF 1360) plus one valve from Ca‘ Piantè; and specimens from Montepetra; four valves from block from Monticino-Limisano – Castelnuovo junction, Brisighella (MSF 1106-1109); five valves from Abisso “Mornig” (MSF 1086, 1090, 1094, 1097, 2120); see Table 1 for measurements.
Remarks.—The assignment of this species toBathymodiolus (sensu lato) is based on its general shape, the change from a hinge with denticles in young specimen to an edentulous hinge in adults, its shellmicrostructure (cf., Génio et al., 2012), and itsmass occurrence at seep deposits. The early juvenile shell shape and adductor and retractor muscle scars, which have been used to identify other fossil bathymodiolins (Kiel, 2006; Kiel and Goedert, 2007; Saether et al., 2010; Amano and Jenkins, 2011; Kiel and Amano, 2013) are not preserved in Bathymodiolus (s.l.) moroniae n. sp. Nelli (1903) and Moroni (1966) had identified this species
as Modiolus (Modiolus) exbrocchii exbrocchii Sacco, 1898, which was named by Sacco (1898) based on an illustration of Modiola brocchii Mayer in Hörnes, 1870 from the Vienna Basin (Hörnes, 1870, p. 345, pl. 45, fig. 13a, b). However, this species differs from B. (s.l.) moroniae by being more elongate and by having a distinct and sharp ridge running from the umbo to the posteroventral margin, whereas B. (s.l.) moroniae is smoothly convex. Furthermore, specimens of B. moroniae with the size of M. exbrocchii as figured by Hörnes (11 cm) are more compact and less elongate that M. exbrocchii. Most similar in general shell shape are specimens of
B. brevior von Cosel, Métivier, and Hashimoto, 1994 living at hydrothermal vents in the Indian Ocean (this population was formerly called B. marisindicus Hashimoto, 2001, but later synonymized with B. brevior, based on molecular data), and B. puteoserpensis von Cosel, Métivier, and Hashimoto, 1994 from the Mid-Atlantic Ridge (von Cosel et al., 1994; Hashimoto, 2001). Another similar species is B. brooksi from the Gulf of Mexico (Gustafson et al., 1998). Interestingly, these three morphologically most similar species all belong to Bathymodiolus sensu strictu and not to the childressi clade. Unlike bathymodiolins at most other fossil seep deposits,
Bathymodiolus (s.l.) moroniae n. sp. occurs mostly as disarticu- lated valves, especially in adult stages.
Bathymodiolus (s.l.) miomediterraneus new species Figure 3
Type specimens.—Holotype: MGGC 21908; paratypes: MSF 1351 (two articulated shells), MSF 1352 (two articulated shells,
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