Thieleella bathypacifica , Geiger, Daniel L. & Mclean, James H., 2010

Geiger, Daniel L. & Mclean, James H., 2010, New species and records of Scissurellidae and Anatomidae from the Americas (Mollusca: Gastropoda: Vetigastropoda), Zootaxa 2356, pp. 1-35: 31-33

publication ID 10.5281/zenodo.275645

persistent identifier

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scientific name

Thieleella bathypacifica

n. sp.

Thieleella bathypacifica  n. sp.

Figures 23–24View FIGURE 23View FIGURE 24

Type material. Holotype ( FMNH 307884)  , shell, operculum and radula mounted on SEM stubs. RV Atlantis, submersible grab, leg. J. Voight.

Type locality. 2572 m, ALVIN Dive 3938, Genesis, East Pacific Rise, 12.811 ˚N, 103.940 ˚W [approximately midway between Acapulco, Mexico, and Clipperton Island]. Sample with anemone and serpulid rocks.

Etymology. Bathy- referring to the deep-sea (bathyal) habitat of the species; -pacifica referring the Pacific Ocean; adjective.

Description. Shell trochiform globular to 1.85 mm. Protoconch of 0.75 whorls, reticulate sculpture, no apertural varix, apertural margin straight. TI of 0.875 whorls, 15 indistinct axial cords, prominent spiral cord forming ridge in position of selenizone, at intersection forming thickenings. TII of at least 1.5 whorls. Shoulder convex, 26 distinct raised axial cords, first spiral line after 0.33 TII whorls, 7 spiral lines after 1.5 whorls on outer two thirds of shoulder, spiral lines running over axial cords. Base convex, barely constricted below selenizone, evenly curving into umbilicus, same density of axial cords as on shoulder, crossed by spiral lines, 23 after 1.25 TII whorls, spiral lines running over axial cords. Selenizone at periphery, keels of moderate strength, high (higher than width of selenizone), regular growth lunules; slit open, with parallel margins.

Operculum round, thin, multispiral, central nucleus, covering aperture.

Radula ( Fig. 20View FIGURE 20). Rachidian trapezoid, central denticle often largest, approximately five denticles on each side ( Fig. 20View FIGURE 20 A –C: R). Lateral teeth 1–3 similar, 6,4, 4 cusps respectively ( Fig. 20View FIGURE 20 B –C: L 1–3). Lateral tooth 4 reduced, hook-shaped, apical denticle largest, two small denticles on inner cutting edge ( Fig. 20View FIGURE 20 C: L 4).

Lateral tooth 5 enlarged by broadening, inner edge with 4–5 denticles, outer edge with three denticles ( Fig. 20View FIGURE 20 B –C: L 5). Inner marginal teeth triangular with approximately 3–4 denticles on each side ( Fig. 20View FIGURE 20 D –E); with posterior projection on upper shaft (except marginal tooth 1: Fig. 20View FIGURE 20 C: M 1); outer marginal teeth spoon or paddle shaped with many fine denticles along apical edge ( Fig. 20View FIGURE 20 E –F).

Differential diagnosis. Thieleella baxteri  from the northeastern Pacific has elevated lamellar axial sculpture. Anatoma janetae Geiger, 2006  , from deep water of the eastern Pacific has a protoconch with flocculent sculpture in spiral orientation, the spiral cord on TI does not form a marked angulation, and shows a marked change of sculpture from predominant axial elements to exclusively spiral elements after 1.25 TII whorls.

Thieleella peruviana  from deep water off Peru, on TI has only a week spiral cord not forming an angulation on the shell’s profile, and has more (42 vs. 15) and weaker axial cords on TI.

Remarks. The only specimen at hand is most likely not fully mature, because the final quarter whorl does not markedly descend along the coiling axis. The specimen is sufficiently distinct to warrant description as new, and material from that depth is unlikely to be collected in the foreseeable future. The specimen was preserved with the body in the shell, hence, was collected live in its natural deep-sea habitat.

The radula of the species shows a thus far unknown detail, namely the posterior projection on the apical portion of the shaft of the marginal teeth from marginal tooth 2 onwards. It is comparable to the food groove known from Tegula funebralis (A. Adams, 1855)  and Liotiidae  (see Morris & Hickman 1981, Hickman & McLean 1990). The occurrence of such a food groove in thus far a single species of Anatomidae  demonstrates further the by now fairly well-documented variability of the radula within Anatomidae  ( Geiger 2006 a, Geiger & Sasaki 2008, Sasaki et al. in press).