Yoldiella spitsbergensis Amano sp. nov.

Fig. 7E–K.

1925 Nuculana sp. 1; Hägg 1925: pl. 3: 6a, 7.

1925 Nuculana sp. 2; Hägg 1925: pl. 3: 8a, b.

1927 Portlandia sp.; Gripp 1927: 31.

1970 Nuculana (Jupiteria) haeggi n. sp.; Anderson 1970: pl. 9: 2a–c (not pl. 9: 1a–c).

ZooBank LSID: urn:lsid:zoobank.org:act: 994EA500-2375-482E-AC28- 450F0DD0DA11

Etymology: Named after the type locality.

Type material: Holotype: ZPAL V.48/17, internal mold (Fig. 7E). Paratypes: NRM-PZ Mo 186241–186242, silicified shells, ZPAL V.48/18– 21, internal molds (Fig. 7F–K).

Type locality: Fossildalen, Spitsbergen, Svalbard.

Type horizon: Cold seep carbonates from the Basilika Formation, upper Paleocene.

Material.— 27 specimens, shells, internal molds and silicified shells, including seven figured (ZPAL V.48/14–18; NRM-PZ Mo 186241–186242) from the upper Paleocene of Fossildalen, Spitsbergen, Svalbard.

Measurements.—The holotype (ZPAL V.48/17): L, 4.9 mm; H, 3.6 mm; W, 3.2 mm. Dimensions range: L, 3.3–6.3 mm; H, 2.8–5.0 mm; W, 1.8–3.8 mm; W/L, 0.41–0.65; H/L, 0.59– 0.85; n = 14. See Table 1 for full list of measured specimens.

Diagnosis.—Small Yoldiella with concave postero-dorsal margin, prominent, centrally located beak, taxodont teeth interrupted by rather wide resilifer, ten teeth anteriorly and nine teeth posteriorly, and narrow and very shallow pallial sinus in front of posterior muscle scar.

Description. —Shell small, moderately inflated, elongate-ovate, equivalve, inequilateral. Surface partly preserved, smooth apart from fine growth lines. Antero-dorsal margin nearly straight, passing into narrowly rounded anterior margin; postero-dorsal margin slightly concave, passing into acutely rounded posterior end; ventral margin broadly arcuate. Two fine, weak internal ridges extending from beak to posterior corner, forming shallow depressed area on internal mold between ridges. Beak prominent, swollen, prosogyrate, situated centrally. Hinge with two series of small teeth, interrupted by rather wide resilifer; anterior series consisting of ten teeth; posterior one with nine teeth. Pallial sinus narrow, very shallow, anterior to posterior muscle scar. Anterior adductor scar elongate-subquadrate; posterior adductor scar small, pyriform.

Remarks. — Hägg (1925) described and illustrated Nuculana sp. 1 and N. sp. 2 from the Cenozoic of Spitsbergen. Gripp 1927) referred to them as Portlandia sp. without explanation. Anderson (1970) proposed Nuculana (Jupiteria) haeggi based on two specimens, of which the holotype (GPIBo 150) has a shape resembling that of Nucula, unlike the shape of Hägg’s (1925) Nuculana spp. 1 and 2. Anderson’s (1970) paratype specimen of Nuculana (Jupiteria) haeggi (GPIBo 151), however, is very similar to both species of Nuculana figured by Hägg (1925). Thus, Yoldiella spitsbergensis Amano sp. nov. is proposed here, based on the new material, Hägg’s (1925) Nuculana sp. 1 and N. sp. 2, and Anderson’s 1970) paratype specimen of Nuculana (Jupiteria) haeggi.

Yoldiella philippiana (Nyst, 1843), now living in the northern Atlantic, Mediterranean Sea and around Japan, is the most similar species in its size and outline to Y. spitsbergensis. However, Y. spitsbergensis Amano sp. nov. differs slightly from Y. philippiana by its larger teeth, larger resilifer, and more obtuse posterior end. Yoldiella nielseni was proposed under the genus Portlandia Mörch, 1857, from the Selandian (middle Paleocene) of Copenhagen, Denmark, by Schnetler (2001). This species is similar to Y. spitsbergensis in its small size (L up to 3.6 mm) and numerous taxodont teeth (12 in both anterior and posterior series of teeth), but differs by having a shorter rostrum and a more obtuse posterior end. Moreover, the very small resilifer of Y. nielseni enables us to separate it from the new species. Yoldiella dortea Heinberg, 1989, from the upper Maastrichtian of Copenhagen, Denmark, is another species that is similar to Y. spitsbergensis in having an ovate shell and a prominent umbo. However, the Cretaceous species can be distinguished from Y. spitsbergensis by its much smaller size (L 2.5 mm) and the low commarginal ribs on its surface, in contrast to fine commarginal growth lines in Y. spitsbergensis.

Stratigraphic and geographic range.—Upper Paleocene cold seep carbonates from the Basilika Formation, Fossildalen and Zachariassendalen, Spitsbergen, Svalbard.