Rubyspira brasiliensis Hasegawa, Fujiwara & Okutani, 2019

Hasegawa, Kazunori, Fujiwara, Yoshihiro, Okutani, Takashi, Sumida, Paulo Yukio Gomes, Kawato, Masaru & Kitazato, Hiroshi, 2019, A new gastropod associated with a deep-sea whale carcass from São Paulo Ridge, Southwest Atlantic, Zootaxa 4568 (2), pp. 347-356 : 349-353

Rubyspira brasiliensis Hasegawa, Fujiwara & Okutani sp. nov.

( Figs 2–5 )

Type material. Holotype MZUSP 141885 ( Figs 2 A–E) . Paratypes, #1 NSMT-Mo 78943 ( Figs 2 F–H); #2 NSMT- Mo 78944; #3 NSMT-Mo 78945 ( Figs 3 , 4 ); #4 JAMSTEC No. 1130057451; #5 JAMSTEC No. 1130057452. All the specimens are stored in 99% ethanol, except paratype #6, which was used for the examination of the soft parts, including the radula. Shell dimensions and depository of the type series are summarized in Table 1.

Additional material examined: MZUSP 141885 (4 exs).

Type locality. São Paulo Ridge, Southwest Atlantic (28˚31.12´S, 41˚39.41´W), at a depth of 4204 m, on and around a whale carcass (see Material section for detail) .

Diagnosis. Shell globose, with an Ampullaria -like appearance, sculptured by fine, crowded spiral cords all over. Umbilicus deeply open. Radula taenioglossate; central, lateral and marginal teeth smooth, completely lacking denticles.

Description. Shell ( Figs 2 , 5 ) rather thin, globose, with Ampullaria -like appearance, covered by pale strawcolored, filmy periostracum, which occasionally bears weak axial lamellae near labral margin. Protoconch missing in all specimens examined due to corrosion. Teleoconch consisting of at least four roundly inflated whorls with moderately constricted suture. Initial teleoconch whorls with sharp angulation at shoulder, which becomes indistinct on lower whorls. Last whorl large, occupying 89% of shell length. Surface sculptured by fine, crowded spiral cords with narrower interspaces all over. Spiral cords rather uniform in thickness and crowded in basal part of last whorl, but becoming stronger and more irregular adapically, especially on sutural ramp area, where strongest spiral cord sometimes forms weak shoulder keel. 15 or more cords on penultimate whorl, some 40–50 on last whorl. Umbilicus narrow but deep, encircled by indistinct fasciole; inner wall ornamented by weak spiral cords. Aperture semi-circular, entire with no anterior sinus or anal notch. Outer lip smooth, neither reflected nor thickened. Inner lip weakly calloused, continuing to nearly straight columellar lip and barely reflected over umbilicus.

Animal ( Fig. 3 ). One probably immature female specimen was examined. Head with relatively large and extremely broad snout and rather blunt cephalic tentacles, lacking pigmented eyes; foot small with propodium and metapodium, separated by narrow lateral groove. Mantle edge simple with small but distinct notch at left corner and simple (not annulate) pallial tentacle in notch in front of anus. Ctenidium well developed, covering nearly one third of pallial roof, and consisting of triangular leaflets. Osphradium relatively small, leaf-like and situated near left corner of pallial roof. Posterior esophagus swollen with soil-like contents, seen through epithelium of mantle floor. Stomach large, comprising large part of ventral side of visceral mass. Rectum also considerably packed with soil-like contents, and sharing most part of right side of pallial roof, especially in its proximal part, leaving little space for gonoduct.

Radula ( Fig. 4A ) taenioglossate, 2-1-1-1-2. Central tooth with ovo-quadrate base and triangular cusp, smooth. Lateral tooth with broad shaft and gently incurved, blunt cusp. Inner and outer marginal teeth gently incurved, with blunt tip; shaft carrying low, lateral wing. All teeth distinctly smooth, with no trace of denticles.

Operculum ( Fig. 4B ) leaf-like in shape, yellowish brown, horny, paucispiral, with indistinct spiral ridge in center. Rather small relative to size of apertural opening.

Variation ( Figs 5 , 6 ). All the specimens larger than 30 mm in shell length (19 examples) were rather uniform both in general shape and sculpture, except for some minor variations mentioned in the description. Only three empty shells in the present material were small (less than 30 mm in length), and they differ considerably from the larger ones in being more narrowly elongate in shape and possessing finer and more crowded spiral ribs. Because of the absence of live-collected specimens of the latter form, both are provisionally regarded herein as forms or growth stages of a single species.

Etymology: The specific epithet brasiliensis refers to the type locality, the São Paulo Ridge, which is located off Brazil.

Remarks. Only two Recent species ( R. osteovora and R. goffrediae) have previously been known in the genus Rubyspira ( Johnson et al. 2010). The present new species is readily distinguished from both by its Viviparus -like globose shell with a widely perforate umbilicus. No other conchologically comparable species in other systematic groups has been found from deep-sea chemosynthetic communities worldwide, including whale falls.

Figures

FIGURE 2. Shell of Rubyspira brasiliensis sp. nov. A-E: holotype, MZUSP 141885. F-H: paratype #1, NSMT-Mo 78943; H, enlarged image of the square area shown in G to show the detail of sculpture. Scales: A-G = 10 mm; H = 5 mm.

FIGURE 3. External anatomy of Rubyspira brasiliensis sp. nov., paratype #3, NSMT-Mo 78945. A: dorsal view with mantle longitudinally cut along the right side of ctenidium. B: ventral view. Abbreviations: cm, columellar muscle; ct, ctenidium; ctn, cephalic tentacle; ebv, efferent branchial vessel; lg, lateral groove; me, mantle edge; mp, metapodium; op, operculum; os, osphradium; pc, pericardium; pt, pallial tentacle; r, rectum; ro, renal organ; s, sole; sn, snout; st, stomach. Scales: A, B = 5 mm; C = 1 mm.

FIGURE 4. Radula and operculum of Rubyspira brasiliensis sp. nov., paratype #3, NSMT-Mo 78945, same specimen as the one illustrated in Figure 3. A. radula, a scanning electron micrograph. B: internal and external views of operculum. Scales: A = 100 µm; B = 1 mm.

FIGURE 5. Comparison of shell morphology of normal (A) and aberrant (B-D) specimens of Rubyspira brasiliensis sp. nov. A. holotype. B-D. aberrant specimens from the type locality obtained together with the holotype, NSMT-Mo 78945. All at the same scale. Scale = 1 mm. Anomalous relative shell length (L2) and width (W2) were measured as shown in A to compare the proportions of these specimens (Figure 6) because of the incomplete conditions of the apical part and outer lip of some specimens. L2 represents the length between the apical margin of the penultimate whorl and the intersection of the basal part of body whorl and aperture in the frontal view.

FIGURE 6. Relationship between shell length and shell width of “normal” (rhomboids), and “aberrant” (gray squares) specimens. Because of the imperfect conditions of some specimens, shell length and width were represented by the parameters indicated in the Figure 5, as L2 and W2, respectively.