Limacina novacaesarea Janssen and Sessa

Janssen, Arie, Sessa, Jocelyn & Thomas, Ellen, 2016, Pteropoda (Mollusca, Gastropoda, Thecosomata) from the Paleocene-Eocene Thermal Maximum (United States Atlantic Coastal Plain), Palaeontologia Electronica (Athens, Greece) 19 (3), pp. 1-26 : 13-14

Limacina novacaesarea Janssen and Sessa sp. nov.

Figures 9.1-7 , 10

zoobank.org/ A893D78B-B268-443C-8585-A9189A97997F

Holotype. RGM 777 219, Figure 9.1-3 (H 1.10, W 1.32 mm). A CT-scan of this specimen is available in Figure 10 .

Type locality. Wilson Lake (Gloucester County, New Jersey, U.S.A.), cored borehole of United States Geological Survey ( USGS), coordinates N39°39′21″, W75°02′31″, drilled 2000, sample 24, depth 98.76-98.82 m .

Stratigraphy. Marlboro Clay (Eocene, Ypresian), 59.14 ky after PETM, nannoplankton zone 10a.

Paratypes. Wilson Lake sample 22 (1 specimen, Figure 9.4-6 ; RGM 777 215a and 1 juvenile specimen, RGM 777 215; and sample 27 (1 specimen; Figure 9.7 , RGM 777 225) ( Table 1).

Additional specimens. Bass River section sample 18 (1 specimen?), RGM 777 297 (specimen lost); Clayton section sample 14 (1 specimen, RGM 777 314 ( Table 2).

Etymology. Nova Caesarea is the Latin name for New Jersey. Limacina gender feminine.

Diagnosis. Limacinid with conical shell, slightly wider than high, of 3¾ rounded whorls, initial whorl planispiral and slightly sunken, umbilicus very wide and deep, occupying almost four tenths of shell diameter.

Description. Shell of rounded conical shape, 1.2 times wider than high, of 3¾ convex whorls, gradually increasing in diameter, attaching at mid-height of preceding whorl. Initial whorl planispiral and somewhat lowered ( Figure 9.6 ), giving the shell a flattened apex in frontal view. Last whorl large, occupying 9/10th of total shell height, regularly rounded at periphery. Aperture large, occupying three quarters of total shell height, elliptical, pointed above, regularly rounded below and with a straight columellar part. Apertural margin simple in available specimens. Base of shell with very large and deep umbilicus occupying 38% of shell diameter (holotype).

Discussion. Limacina novacaesarea resembles L. perforata Janssen , in Janssen et al. (2013, p. 30, figure 12) from unnamed rocks of latest Ypresian to earliest Lutetian age in the Soh Area, Iran. That species reaches considerably larger dimensions (W = 2.4 mm) but has the same number of whorls, has a lower apical shell part the apex of which is not planispiral, its whorls attach much higher on the preceding one, and its umbilicus is narrower (about 20% of shell diameter) with a faint ridge bordering the shell’s basal plane. Finally, in L. perforata the columellar part of the apertural margin has a clear abaxial curvature, not seen in L. novacaesarea .

Distribution. The new species is only known from the localities specified above.

Figures

FIGURE 9. Limacina novacaesarea Janssen and Sessa sp. nov. 1-3, Holotype, Wilson Lake section, sample 24, depth 98.76-98.82 m, RGM 777 219; 1: apical; view, 2: apertural view, 3: umbilical view. 4-6, Paratype 1, Wilson Lake section, sample 22. Depth 98.15-98.21 m, RGM 777 215a; 4: apical view, 5: apertural view, 6: oblique apical view to show lowering of initial whorl. 7, Paratype 2, Wilson Lake section, sample 27, depth 99.67-99.73 m, RGM 777 225; apertural view of poorly preserved, slightly depressed specimen.

FIGURE 10. Limacina novacaesarea Janssen and Sessa sp. nov. Computed tomography (CT) scan of the specimen pictured in Figure 9.1-3. Resolution 4.0 micrometer/voxel, 185 kV, detector exposure timing 750 ms. For animated version, see online at palaeo-electronica.org/content/2016/1662-pteropoda-from-the-usapetm. By clicking on the image, the interactive 3D model is activated, and the reader can use the mouse to rotate the specimen and change magnification.