Lucinoma kosatorea, Kiel & Aguilar & Kase, 2020

Kiel, Steffen, Aguilar, Yolanda M. & Kase, Tomoki, 2020, Mollusks from Pliocene and Pleistocene seep deposits in Leyte, Philippines, Acta Palaeontologica Polonica 65 (3), pp. 589-627 : 605-606

Lucinoma kosatorea sp. nov.

Fig. 17 .

Zoobank LSID: urn:lsid:zoobank.org:act:47983DA6-3C79-49B9-A174-40BE6795CA49

Etymology: By anagram from kastoroae , a closely related species of Lucinoma .

Type material: Holotype NMNS PM 28164 , an isolated left valve.

Type locality: Cambantug Point , Leyte, Philippines .

Type horizon: Lower Pleistocene part of the Bata Formation .

Material.—The holotype only.

Dimensions (in mm).—NMNS PM 28164, L = 52.7, H = 46.0.

Diagnosis.—Medium-sized, little-inflated Lucinoma , outline oval with acutely rounded anterior margin; rounded-pentagonal, umbones small, pointed, prosogyrate; surface sculpture of numerous densely spaced, sharp commarginal ribs, several smaller sharp ridges in interspaces; posterodorsal sulcus very shallow; lunule long, narrow; ligament nymph long.

Description.—Weakly, evenly inflated shell with small, pointed umbones, greatest width at middle of shell; anterodorsal margin undulating, slightly concave, with distinct angulation at transition to acutely rounded anterior margin; posterodorsal margin convex, posterodorsal area broad, bordered by indistinct, low ridge at which commarginal ribs are deflected; ventral margin almost evenly convex, without distinct transitions to anterior margin, and weak angulation at transition to posterior margin; escutcheon lanceolate; lunule long, moderately deep; hinge plate narrow and thick, two thin cardinals in left valve, both pointing downward; thin, elongate anterior lateral tooth in left valve; ligament nymph long, narrow; anterior adductor muscle scar long and narrow, reaching down to 70% of shell height, detached slightly from pallial for c. 70% of its length; posterior adductor muscle scar rounded-oval, its lower end situated at about mid-height of shell; interior of ventral margin marked by two thin ridges with groove in between.

Remarks.—Very similar in shell shape is the Pleistocene Japanese species Lucinoma aokii Hirayama, 1958 , but it is larger than L. kosatorea (L = 76.0 mm vs. L = 52.7 mm in L. kosatorea ), has a broader lunule with a clearly delimited margin, the hinge plate has an excavated area posterior to the umbo, and the ligament nymph is much narrower than in L. kosatorea ( Hirayama 1958) . A specimen reported as L. aokii from a Pleistocene seep deposit on the Boso Peninsula in Japan ( Shibasaki and Majima 1997: 1068, fig. 4.12): differs from the holotype of L. kosatorea by having a shorter but broader hinge plate, a straighter anteroventral margin, and a distinct external ridge running from the umbo to the anterior shell margin.

Lucinoma canudai , L. velosoi , and L. tinagoensis are much more inflated than Lucinoma kosatorea . A similarly acutely rounded anterior margin is seen in the extant Lucinoma anemiophila Holmes, Oliver, and Sellanes, 2005 from methane seeps off of central Chile. But L. anemiophila has a truncated, angular posterior margin and a more distinctive posterior ridge than Lucinoma kosatorea ( Holmes et al. 2005) .

Stratigraphic and geographic range.—Early Pleistocene, Leyte, Philippines.

Figures

Fig. 17. The lucinid bivalve Lucinoma kosatorea sp. nov. from the Pleistocene Cambantug Point seep deposit, Leyte, Philippines, holotype NMNS PM 28164, an isolated left valve; dorsal side (A1), exterior surface showing sculpture (A2), interior surface showing muscle scars and pallial line (A3), close-up on hinge (A4).