Filamussium, Waller, 2006

Waller, Thomas R., 2006, Phylogeny of families in the Pectinoidea (Mollusca: Bivalvia): importance of the fossil record, Zoological Journal of the Linnean Society 148 (3), pp. 313-342 : 342

FILAMUSSIUM , GEN. NOV. ( FIG. 7A–C )

Type species: Pecten schafhäutli Winkler, 1859 (= Pecten velatus Schafhäutl, 1852; non Pecten velatus Goldfuss, 1833), Upper Triassic, Kothalpe am Breitenstein, Germany. Spelling automatically emended to Pecten schafhaeutli .

Diagnosis: Propeamussiidae with right valve less convex than left or nearly flat, exterior of right valve smooth, that of left valve with intercalated radial costae of more than one order and finer, closely spaced commarginal lirae. Outer calcitic columnar prismatic layer of right valve consisting of small, polygonal prisms randomly arranged, not commarginally ordered or alternating in size, directly overlying an inner crossed-lamellar aragonitic layer in central region of disk; outer layer of left valve nonprismatic calcite, inner layer crossed-lamellar aragonite. Internal ribs present on both valves, widely and regularly spaced with distal termini well separated from ventral margin of disk; filosus structure present on inner surface of outer calcitic layer of left valve. Dentition of right valve with well-developed resilial teeth, fitting into well-developed resilial sockets on left valve.

Comparison: Filamussium differs from members of the Entolioididae in having internal ribs. The new genus differs from other genera of Propeamussiidae in having a filosus structure on its left valve and in having internal ribs that were probably originally aragonitic rather than calcitic.

Included species: In addition to the type species, the new genus includes Pecten (Variamussium) klushaensis Lees, 1934 and P. (V.) yukonensis Lees, 1934 both from the Upper Triassic (upper Norian Suessi Zone; Tozer, 1967: 80) of the Laberge area, Yukon.

Occurrence: See preceding discussion of clade 4 – Propeamussiidae .

Figures

Figure 7. Filamussium schafhaeutli (Winkler, 1859), gen. nov., Upper Triassic (Norian/Rhaetian). A, a compound external mould of the left valve, Kössener Schichten, Kotalm, Schweinsberg bei Miesbach, Germany and BSPHG 1916-I-208. B, detail in the centre of (A) showing the superimposed internal filosus structure, external radial costae, and calcite-filled imprints of internal ribs. C, exterior of a right valve, Kössen Formation, Kendelbachgraben, Austria, USNM(P) 530053. Scale bars = 10 mm.