Adamussium auristriatum Quaglio et al., 2008
QUAGLIO, F., L. E. ANELLI, P. R. DOS SANTOS, J. A. DE J. PERINOTTO & A. C. ROCHA-CAMPOS. 2008. Invertebrates from the Low Head Member (Polonez Cove Formation, Oligocene) at Vauréal Peak, King George Island, West Antarctica. Antarctic Science, 20 (2): 149-168 [p. 155, figs. 9a-q]
2008 Adamussium auristriatum Quaglio et al., 2008
F. Quaglio et al., 2008, figure 9.
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«Material. Holotype, internal mould of articulated valves (5457b), external mould of right valve (5457a). Paratypes, internal moulds of articulated valves (5458b); internal moulds of right valve (5301a, 5361, 5405); external moulds of right valve (5301b, 5394, 5458a); external mould of left valve (5428).
Etymology. From Latin auris = ear and striatum = striated, referring to the radial costae on the anterior auricle. Diagnosis. Umbonal angle around 1308; commarginal sculpture of lirae, weakly marked, almost equally and widely spaced down the entire shell; RV auricles almost symmetrical, posterior and anterior with well defined commarginal lines, anterior auricle with radial costae. Description. Shell varying from moderate to small in size, subcircular; dorsal margin short, ventral margin wide and rounded; equant; very compressed, with moderately convex valves; beaks orthogyrate; umbonal angle wide (around 130°); valves slightly opisthocline (mean AVH/PVH = 1.10); radial sculpture of around 10-15 main plicae, intercalated with lower and less developed plicae; commarginal sculpture of lirae, weakly marked, almost equally and widely spaced down the entire shell; microsculpture of narrow antimarginal ridgelets; hinge line almost straight; RV auricles highly symmetrical (mean AOL/POL = 1.04), posterior and anterior with well defined commarginal lines, anterior auricle rounded, with 4-6 radial costae; byssal notch acute, ctenolium with six byssal teeth (in 5457b). Comparison. Adamussium auristriatum sp. nov. differs from the Pleistocene–Recent A. colbecki colbecki in its smaller size, its equally convex valves, its narrower umbonal angle, its more equally spaced and weaker commarginal sculpture, and the presence of radial costae on the RV anterior auricle. Adamussium auristriatum sp. nov. differs from A. colbecki cockburnensis from the Late Pliocene Cockburn Island Formation (Jonkers 2003) in its opisthocline valves, narrower umbonal angle, more symmetrical auricles, weaker commarginal sculpture and the presence of radial costae on the RV anterior auricle. The auricles and umbonal angle of A. alanbeui Jonkers, 2003 are very distinct from those of A. auristriatum sp. nov., which
contains commarginal sculpture and symmetric auricles. However, the pattern of antimarginal microsculpture is very similar in the two. The specimens of A. alanbeui from the type-area of Polonez Cove Formation (initially identified as Eburneopecten sp. by Gazdzicki & Pugaczewska 1984) are poorly preserved, but the sculpture pattern is very unlike A. auristriatum sp. nov. Comparison with other Adamussium species is presented in the Table V. Remarks. Adamussium colbecki colbecki is known from Pliocene and Pleistocene deposits of West Antarctica, and from the Recent of the Southern Ocean (Jonkers 2003). Adamussium colbecki cockburnensis is recorded only from Late Pliocene Cockburn Island Formation (Jonkers 2003). One specimen of A. alanbeui from the Polonez Cove Formation, presumably from the Low Head Member, at Godwin Cliffs, Lions Rump area, was identified and illustrated by Jonkers (2003). This species differs from other species of Adamussium in lacking radial costation and commarginal lirae (Jonkers 2003). Together with A. alanbeui, A. auristriatum sp. nov. is the oldest record of the genus and probably represents a closer relative to the Recent A. c. colbecki than A. colbecki cockburnensis and A. alanbeui do. Despite the resemblance of the Oligocene A. auristriatum sp. nov. to the Recent A. colbecki colbecki and the Pliocene A. colbecki cockburnensis, it is reasonable that they comprise three distinct, but closely related taxa.» FERNANDA QUAGLIO, LUIZ E. ANELLI, PAULO R. DOS SANTOS, JOSÉ A. DE J. PERINOTTO & ANTONIO C. ROCHA-CAMPOS, 2008
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