Ammonicera danieli, 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 : 477-478

Ammonicera danieli sp. nov.

Figure 5A–F

Zoobank LSID. urn:lsid:zoobank.org:act:566B2F63-DD2C-4F23-89CA-33A9148380A0

Material. (2 specimens) Holotype: MIMB 41139 ; Paratype: MIMB 41140 , 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 Daniel Geiger (SBMNH) for his contributions to the study of microgastropods.

Diagnosis. Ammonicera with protoconch nucleus covered by small irregular depressions, wide central cord toward the teleoconch with narrow outer spiral cord, narrow axial ribs; teleoconch with wide, smooth axial ribs and one weakly visible subperipheral groove on apical and basal surfaces.

Description. Shell planispiral, tightly coiled, maximum shell diameter 0.53–0.55 mm. Protoconch of approximately 1 whorl, 0.10-0.11 mm in maximal diameter; boundary between protoconch and teleoconch poorly marked, without scars. Nucleus of protoconch covered irregular small depressions; rest of protoconch with wide central cord positioned mid-whorl, but near teleoconch located closer to inner margin of outer suture; very narrow outer spiral cord located closer to inner margin of outer suture; apical side of protoconch with 18–21 very narrow axial ribs crossed by outer spiral cord and connected with outer side of central cord; axial ribs have more irregular form and position on basal side of protoconch. Teleoconch approximately 1.6–1.7 whorls, with one weakly visible subperipheral groove on apical and basal surfaces, without spiral cords. Apical and basal surfaces sculptured by wide and smooth axial ribs, 18–20 ribs per whorl, with interspaces c. 0.8–1.2 times their width. Aperture round.

Comparisons. Ammonicera danieli sp. nov. is similar to A. japonica sensu Sleurs, 1985 described from Papua New Guinea ( Sleurs 1985). Both species have a protoconch with numerous axial ribs, but these ribs are crossed by one spiral cord in A. danieli and two spiral cords in A. japonica sensu Sleurs. It should be noted that A. japonica sensu Sleurs is not conspecific with A. japonica Habe, 1972 from Japan and Korea (see Waki et al. 2016).

Remarks. Ammonicera danieli is the third Paleogene species of the genus Ammonicera recorded from western North America. Together, Ammonicera benhami , A. rolani , and A. danieli are, so far, the only fossil record of the genus for the North Pacific Ocean. These fossils indicate species of Ammonicera have inhabited the eastern North Pacific Ocean since at least since middle Early Eocene time, approximately 50 Ma, and possibly longer.

Figures

FIGURE 5. Ammonicera danieli sp. nov. (SEM), holotype MIMB 41139, apical view (A, B) and lateral view at oblique angle (C); paratype MIMB 41140, umbilical (D, E) and apical (F) views; general view (A, C, E); detail of the protoconch (B, D, F). Scale bars: A, C, E—100 μm; B, D, F—20 μm.