Carychium nashuaense Jochum, Lee & Portell, 2023

Jochum, Adrienne, Bochud, Estee, Haberthuer, David, Lee, Harry G., Hlushchuk, Ruslan & Portell, Roger W., 2023, Fossil Carychiidae (Eupulmonata, Ellobioidea) from the Lower Pleistocene Nashua Formation of Florida, with the description of a new species, ZooKeys 1167, pp. 89-107 : 89

Carychium nashuaense Jochum, Lee & Portell sp. nov.

Figs 9 , 10 , 11 , 12

Type material.

Holotype: USA, Florida • SH = 1.58 mm, SW = 0.72 mm, PH = 0.56 mm, PW = 0.53 mm; Orange County, Orlando; 28.4489, -81.0375 (WGS84) encompassing 500 m radius; Oct. 2021; R. Portell and H. Means leg.; NMBE 577017. Paratypes: USA, Florida • 2 figured shells; same data as for holotype; NMBE 577018-577019 • 3 shells; same data as for holotype; UF 335884-335886.

Measurements.

SH = 1.43-1.63 mm, SW = 0.68-0.69 mm, PH = 0.53-0.57 mm, PW = 0.51-0.54 mm.

Diagnosis.

Shell 1.54 mm (mean) in height, elongate-pupiform with elliptical-ovate shaped aperture, thickly callused double peristome with a deeply set columellar-basal apertural barrier and a pronounced parietal denticle. Internally, C. nashuaense sp. nov. has a highly sinuate, tightly coiled, double structured lamellar configuration.

Description.

Shell medium-sized for the genus, elongate-pupiform, robust, with 5 tumid whorls and a large aperture. PH is 36% of SH, elliptical-ovate, the inner callused, upper palatal side is somewhat angular. Protoconch bulbous, smooth, and shiny; teleoconch ornamented by equidistantly aligned, broad ribs. Suture deeply impressed, not descending towards the aperture. Whorl profile strongly convex, especially on middle whorls, less so on body whorl. Peristome thickly callused and doubled with a thinner, sharp rim at the margins. Columellar portion broadly expanded, heavily callused, palatal lip thicker at mid-section. Outer, basal and columellar margins reflected, parietal callus thick. Two apertural barriers, visible in apertural view; large prominent deeply set parietalis situated almost medially with a slight downward tendency, not reaching margin of peristome; small columellaris near the base of the columella. The moderately thick parietalis is set deep and advances a short distance beyond the thickly callused inner margin of the peristome in umbilical view. Umbilicus chink-like. From apical view, the spire is dominated by the tumid third and fourth whorls causing the body whorl to completely disappear under their convexity. The reflected, wing-like apertural lip projects away from the spire in apical and umbilical view (Figs 9A , 10 C, F ). Internally, two lamellae spiral down the columella for at least the last whorl and a half, terminating in the parietalis and columellaris in the aperture. The major lamella is highly sinuate, flipping over in frontal, apertural view (Figs 10A , 11A , 12A ). It forms a spatulate, wing-like extension in the penultimate whorl just above the junction with the body whorl in aperture facing right and aperture facing left view (Figs 10D-E , 11D-E , 12D-E ). The second, low, tightly coiling lamella proceeds underneath the elaboration of the major lamella, internally forming a conspicuous knob on the columella at mid-section of the body whorl before dropping straight down towards the base of the columella (Figs 10B , 11B , 12B ).

Differential diagnosis.

Carychium nashuaense sp. nov. appears morphologically to be a cross between C. belizeense Jochum & Weigand, 2017 and C. hardiei Jochum & Weigand, 2017. These two species are much larger than C. nashuaense sp. nov. and have smoother shells. Even though C. nashuaense sp. nov. was buried under marl for about 2 million years, the ribbing structure on the teleoconch is remarkably well preserved. The shell shape with the highly convex third and fourth whorls extending over the body whorl, preventing it from being observed in apical view, is most similar to that of C. belizeense . On the other hand, the prominent parietalis proceeding far above the peristome edge (umbilical view) and the elliptical apertural form and reduced peristome thickness in that species differs significantly from that of the highly callused C. nashuaense sp. nov. Internally, the lamella of C. Carychium belizeense is highly sinuate and complexly structured on a very compact and short columella.

Etymology.

The specific epithet refers to this species being found in the Freshwater Marl Bed of the Nashua Formation.

Stratigraphic occurrence.

Freshwater Marl Bed (middle nonmarine layer) (FLMNH IP locality OR022), Lower Pleistocene Nashua Formation.

Figures

Figure 9. Light microscopic images of Carychium nashuaense sp. nov. A-G holotype (NMBE 577017) H-N paratype (NMBE 577018) O-U paratype (NMBE 577019). Scale bar: 1 mm.

Figure 10. 3 D visualizations of X-ray micro-CT data of Carychium nashuaense sp. nov. holotype (NMBE 577017) A apertural view showing sinuate lamella B dorsal view showing entire columellar axis C umbilical view showing thick peristome and parietalis D aperture facing right view E aperture facing left view F apical view. Scale bar: 1 mm.

Figure 11. 3 D visualizations of X-ray micro-CT data of Carychium nashuaense sp. nov. paratype (NMBE 577018) A apertural view showing sinuate lamella B dorsal view C umbilical view showing thick peristome and parietalis D aperture facing right view E aperture facing left view F apical view. Scale bar: 1 mm.

Figure 12. 3 D visualizations of X-ray micro-CT data of Carychium nashuaense sp. nov. Paratype (NMBE 577019) A apertural view showing sinuate lamella B dorsal view showing entire columellar axis C umbilical view showing thick peristome and parietalis D aperture facing right view E aperture facing left view F apical view. Scale bar: 1 mm.