Kiel and Taviani—Miocene methane-seep bivalves from Italy
459
Figure 13. Archivesica strigarum new species from the middle to late Miocene seep deposits in northern Italy: (1) paratype (MGGC 21929) from Sasso delle Streghe, left valve showing the round anterior adductor muscle scar; (2–5) holotype (MZB 28095) from Sasso delle Streghe, internal mold; (2) left valve, (3) dorsal view, (4) close-up of hinge area, (5) silicon rubber cast of hinge area; (6, 7) paratype (MRSN PU 40611.01), small specimen from Deruta. Abbreviations: aprs, anterior pedal retractor scar; LV, left valve; RV, right valve.
Remarks.—These specimens share all features of A. aharoni, but are slightly smaller and consistently lack the posterior ridge and groove that can be seen in many specimens of A. aharoni from the type locality. Furthermore, the posterior part of the pallial line and the posterior adductor muscle scar can be more clearly seen than in specimens of A. aharoni from the type locality, but this might be a taphonomic artifact.
Archivesica strigarum new species Figure 13
2001 Calyptogena sp. Taviani, fig. 20.8a.
Type specimens.—Holotype: MZB 28095, internal mold from Sasso delle Streghe (87 ×38 ×24.5 mm). Paratypes: MGGC 21929, specimen with partially preserved external features from Sasso delle Streghe; MRSN PU 40611, small specimen from Deruta (41 ×19× 11.5mm).
Diagnosis.—Elongate Archivesica, beak situated anteriorly at ~26% of total shell length; onset of pallial line at posteroventral margin of anterior adductor muscle scar; no pallial sinus.
Occurrence.—Middle Miocene seep carbonates in northern Italy.
Description.—Elongate veneriform shell (max. dimensions L=95mm,H=45mm,W=30mm)with beak situated in anterior third of shell; anterior margin well rounded, posterodorsal margin only slightly tapering, posterior margin broadly rounded, ventral margin gently rounded, shell surface smooth except for growth lines. Anterior adductor muscle scar broadly oval, bordered pos- teriorly by distinct ridge; pedal retractor scar oval, distinct from adductor muscle scar; onset of pallial line at posteroventral margin of anterior adductor muscle scar, obliquely cutting across anteroventral shell margin; pallial sinus small, shallow, pointed.RV hinge with thick cardinal 1; cardinal 3a thick, elongate; cardinal 3b thin and very long; LV hinge with cardinal 2a thick, elongate; cardinal 2b thin and close to almost equally shaped cardinal 4b.
Etymology.—For the type locality at Sasso delle Streghe (the witches’ rock; Striga Latin for witch).
Materials.—Slab with five decalcified shells from Sasso delle Streghe (MGGC 23000); one incomplete articulated mold (MSF 1357); one specimen from Deruta (MRSN PU 40610).
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