Leptogyra squiresi, Kiel & Goedert, 2007

Kiel, Steffen & Goedert, James L., 2007, New mollusks associated with biogenic substrates in Cenozoic deep-water sediments of Washington State, Acta Palaeontologica Polonica 52 (1), pp. 41-52 : 42-43

Leptogyra squiresi sp. nov.

Figs. 3A–C .

2006 Leptogyra n. sp.; Kiel and Goedert 2006b: 549, fig. 2F, G.

Derivation of the name: For Richard L. Squires, Northridge.

Holotype: USNM 528923 . Well−preserved specimen with slightly damaged apertural margin.

Paratypes: USNM 528922 , 532037 .

Type locality: USGS locality 26905, associated with wood fragments, Satsop River , Mason County, Washington State, USA .

Type horizon: Uppermost Eocene, Lincoln Creek Formation.

Material.— The type material and several unnumbered specimens from the type locality are deposited in the USNM .

Diagnosis.—Protoconch of one−half whorl, 190 ̊m diameter; with polygonal and spiral sculpture; a sinuous bulge near the aperture, transition to teleoconch marked by a fine ridge. Teleoconch low−spired skeneiform, apical angle about 125 °, two and one−half convex, slightly shouldered whorls with fine spirals and prosocline axial ribs. Shell composed mainly of crossed−lamellar structure, with fine shell pores almost perpendicular to shell surface.

Description.—The protoconch is sculptured by a polygonal pattern on the first quarter whorl and spirally arranged wrinkles on the second quarter, the bulge near the aperture is approximately 15 microns wide. Suture of teleoconch deep; whorls sculptured by twelve fine spiral cords, with strongly prosocline ribs on earlier whorls, later whorls with strong collabral growth lines only; the growth lines on the base are opisthocyrt; aperture broken, umbilical area covered by sediment in all specimens. Shell wall of the last whorl about 70 ̊m thick, composed of a thin (<10 ̊m) simple prismatic layer, and a thick layer of crossed−lamellar structure. The shell is perforated by thin (approximately 0.1 ̊m wide) pores. The holotype is 1.13 mm high and has a diameter of 1.61 mm.

Discussion.—This species is very close in shape to the Recent North Atlantic Leptogyra verrilli Bush, 1897 and L. constricta Marshall, 1988 . From the latter it differs by its growth lines which are less prosocline. In L. verrilli the protoconch is larger (0.24 mm measured from Marshall 1988: fig. 2C) than in L. constricta and in L. squiresi . A Leptogyra species that inhabits hydrothermal vents rather than sunken wood is L. inflata Warén and Bouchet, 1993 , which has finer sculpture than L. squiresi , and has, with 200 microns diameter, the smallest protoconch of the known recent species. The Recent Alaskan L. alaskana Bartsch, 1910 , which is geographically the closest species to L. squiresi , has a lower spire than L. squiresi , but whether this species indeed belongs to Leptogyra is uncertain. Bartsch (1910) described the protoconch to consist of one−and−a−half whorls, which contradicts a position within Leptogyra , but the holotype is poorly preserved and the number of whorls of the protoconch was impossible to determine under a light microscope. However, Bartsch’s (1910: 136) description of the protoconch as “light yellow horn color” cannot be confirmed. Leptogyra squiresi is the only species of Leptogyra known from the fossil record. Stratigraphic and geographic range.—Known only from the uppermost Eocene in Washington State, USA.

Figures

Fig. 3. Gastropods from Eocene to Miocene whale− and wood−falls in Washington State. A–C. Neomphalid Leptogyra squiresi sp. nov., from a uppermost Eocene wood−fall at the Satsop River (USGS loc. 26905). A. Holotype USNM 528923 in apertural (A1) and apical (A2) views. B. Protoconch of paratype, USNM 528922. C. Paratype showing shell microstructure, arrows indicate shell pores, USNM 532037. D, E. Buccinid Colus sekiuensis sp. nov. D. Paratype USNM 531404 from a upper lower Oligocene wood−fall at Murdock Creek (USGS loc. 26898−A); D1, sculptural detail; D2, lateral view. E. Holotype UWBM 97933 from a upper lower Oligocene whale−fall at Murdock Creek (USGS loc. 26898) in apertural (E1) and lateral (E2) views.