Conchocele majimai, 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 : 592-593

Conchocele majimai sp. nov.

Fig. 3 .

Zoobank LSID: urn:lsid:zoobank.org:act:5B70D6CF-1E10-454E-82EE-4E85D1834913

Etymology: In honour of Ryuichi Majima (Yokohama National University), who cooperated field work.

Type material: Holotype NMP-2159, an isolated left valve; paratype NMNS PM 28171 , an isolated right valve.

Type locality: Liog-Liog Point , Leyte, Philippines .

Type horizon: Upper Pliocene part of the Bata Formation .

Material.—The type material and two unnumbered specimens from the type locality.

Dimensions (in mm).—NMP-2159, L = 72.0, H = 60.0; NMNS PM 28171, L = 68.0, H = 58.0.

Diagnosis.—Large Conchocele with slightly concave anterior margin; broad posterodorsal area with low median ridge, bordered by deep, slightly curved posterior sulcus causing slight indentation of posterior margin; ventral margin straight, broadly curving into posterior margin.

Description.—Large, well-inflated shells, W/H ratio of one valve 0.30–0.33, umbones terminal, blunt, prosogyrate; anterior margin long, slightly concave; anterodorsal area broad with blunt internal ridge starting at umbo, ending at 2/3 of length anterodorsal area; anterior half of ventral margin straight, then turning dorsally in broad curve until reaching posterior end of shell; dorsal margin evenly and slightly convex, transition to posterior margin marked by distinct corner; posterodorsal area broad, bordered by deep, sulcus that is curved on first half of shell, nearly straight on second half, and causes an indentation on the posterior shell margin; outer surface with fine, irregular growth lines.

Remarks.— Conchocele majimai differs from Conchocele visayaensis sp. nov. described below by its almost straight posterior sulcus, the broader posterodorsal area, and its straight ventral margin. The extant Conchocele novaeguinensis Okutani, 2002 from northern Papua New Guinea differs from C. majimai by its strongly coiled umbo (Okutani 2002). The extant Conchocele ochotica ( Krishtofovich, 1936) (= Thyasira disjuncta var. ochotica Krishtofovich, 1936 ) has a more distinctive (= deeper) posterior groove above the posterior ridge, and a narrower posterodorsal area than Conchocele majimai ( Krishtofovich, 1936) . Also extant North Pacific specimens illustrated as Conchocele bisecta or Conchocele disjuncta ( Coan et al. 2000; Kamenev et al. 2001; Kharlamenko et al. 2016) have a narrower posterodorsal area than Conchocele majimai . A specimen illustrated as Conchocele sp. from Broken Water Bay in Papua New Guinea ( Samadi et al. 2015: fig. 2F) has a more rounded ventral margin and a narrower posterodorsal area than Conchocele majimai . The Miocene holotype of Conchocele bisecta has a much more rounded outlined and a more acutely rounded anterior margin than both Conchocele majimai and Conchocele visayaensis described below.

Stratigraphic and geographic range.—Late Pliocene, Leyte, Philippines.

Figures

Fig. 3. The thyasirid bivalve Conchocele majimai sp. nov. from the Pliocene Liog-Liog Point seep deposit in Leyte, Philippines. A. Paratype NMNS PM 28171, an isolated right valve; outer shell surface (A1), anterior side (A2), posterodorsal margin (A3). B. Holotype NMP-2159, an isolated left valve; posterodorsal margin (B1), anterior side (B2), outer shell surface (B3).