Ammonicera rolani, Chernyshev & Goedert, 2021

Chernyshev, Alexei V. & Goedert, James L., 2021, New species of latest Eocene / earliest Oligocene microgastropods (Heterobranchia Orbitestellidae and Omalogyridae) from the Gries Ranch Formation, Lewis County, Washington State, USA, Zootaxa 4981 (3), pp. 469-480 : 475

Ammonicera rolani sp. nov.

Figure 4A–G

Zoobank LSID. urn:lsid:zoobank.org:act:8194CEF8-2A15-4395-840C-EF54CB284C35

Material. Holotype: MIMB 41137 ; Paratypes: MIMB 41138 (lot of 4 specimens) , SBMNH 467094 (lot of 2 specimens), all from type locality .

Type locality. LACMIP locality 41621; Gries Ranch Formation , Lewis County, Washington State, USA; latest Eocene or earliest Oligocene , 33.5–34.7 Ma (latest Priabonian or earliest Rupelian; Prothero & Burns 2001) .

Etymology. Named for Emilio Rolán (University of Santiago de Compostela) for his contributions to the study of micromollusks.

Diagnosis. Ammonicera with protoconch sculptured by two spiral cords (prominent central and low outer), separated by a broad spiral groove possessing a wrinkled texture, teleoconch with one subperipheral groove on both apical and basal surface, low node-like axial ribs, fine spiral lirae.

Description. Shell planispiral, tightly coiled, maximum shell diameter 0.51–0.59 mm. In holotype, protoconch with approximately 0.8 whorl, 0.12 mm in maximal diameter, two conspicuous scars (between protoconch and transition zone, and between transition zone and teleoconch—for terms see Oliver & Rolán 2015) present; in one paratype (MIMB 41138–1) protoconch approximately 1.0 whorl, scar between protoconch and transition zone poorly marked ( Fig. 4D ); in other paratypes scar between protoconch and transition zone not detected ( Fig. 4G ). Protoconch sculptured with two spiral cords and one broad spiral groove between these cords; central cord positioned mid-whorl, broad and prominent; low and narrow outer spiral cord located closer to inner margin of outer suture than to central cord; broad groove between cord has wrinkled sculpture in better preserved shells. Surface of the protoconch finely pitted; very small pits form fine spiral sculpture of both protoconch and protoconch-teleoconch transition zone. Teleoconch of 1.1–1.75 whorls, with one subperipheral groove on apical and basal surfaces. Apical and basal surfaces additionally sculptured by nodelike axial ribs, 18–22 ribs per whorl, with interspaces c. 1–1.5 times their width. Secondary spiral sculpture of the teleoconch composed of numerous very fine lirae ( Fig. 4E ). Aperture round.

Comparisons. Ammonicera rolani sp. nov. appears to be closely related to A. benhami ; both species possess similar protoconch sculpture, but the new species can be distinguished from A. benhami by the absence of subperipheral spiral cords and hence more evenly rounded whorls with less prominent nodes on the teleoconch.

Remarks. Ammonicera rolani is the second Paleogene species of the genus Ammonicera from western North America.

Figures

FIGURE 4. Ammonicera rolani sp. nov. (SEM), holotype MIMB 41137, umbilical view (A, B); paratypes MIMB 41138–1, lateral view (C, E), MIMB 41138–2, apical view (D), and MIMB 41138–2, umbilical view at oblique angle (F, G); general view (A, C, F); detail of the protoconch (B, D, G), arrows indicate scar between protoconch and transition zone, arrowheads indicate scar between transition zone and teleoconch; spiral microsculpture of the teleoconch (E). Scale bars: A, C, F—100 μm; B, D, G—20 μm; E—10 μm.