Thieleella peruviana, 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 : 28-31

Thieleella peruviana n. sp.

Figures 20–22

Type material. Holotype ( UF 383672 , shell, mounted soft parts with radula removed, mounted radula) . Four paratypes (UF 424420, fluid preserved shells with preserved bodies), from type locality. Type locality. 991–1015 m, off Northern Peru [ approximately 175 km WNW of Trujillo ], Peru-Chile Trench , Peru, 7.983˚S, 80.617˚W.

Etymology. Named after its provenance from off Peru.

Description. Shell medium size for genus (up to 3.0 mm), trochoid globular. Protoconch of 0.75 whorls, reticulate sculpture, (see arrows on Fig. 20 ) condition of apertural varix and shape of apertural margin unknown. TI of 1 whorl, approximately 42 fine axial cords, spiral cord in position of selenizone. TII of 2.5 whorls, suture impressed, below periphery of previous whorl. Shoulder convex, approximately 43 axial cords on first whorl, spiral lines starting at onset of selenizone, approximately 10 after 1 whorl, 12 at apertural margin of holotype, slightly irregularly spaced between suture and selenizone. Base with slight constriction below selenizone, 1.5 times as many axials cords as on shoulder, approximately 28 spiral lines stronger than on shoulder, forming points at intersection with axials. Umbilicus narrow, weak funiculus. Aperture D-shaped with columellar portion almost straight. Selenizone slightly above periphery; keels moderately strong, moderately elevated; lunules irregular, distinct; slit with parallel margins.

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

Radula: rachidian tooth triangular, cusp with central denticle larges, 4–5 denticles on each side, decreasing in size laterally. Lateral teeth 1–3 similar, decreasing in size two fold, 4,4,3 denticles on outer edge of cusp, respectively. Lateral tooth 4 reduced, hook-shaped. Lateral tooth 5 enlarged by broadening, cusp with penultimate denticle largest, one smaller one on outer edge, five on inner edge, decreasing in size towards base. Marginal teeth hook-shaped with many small denticles on each side. Radular interlock of central field moderate.

Body pale cream in color. Head with non-papillate cephalic tentacles (ct), no eyestalk or eye, suboptic tentacle (ct) present, accessory cephalic tentacle (act). Four epipodial tentacles (et), biserially papillate on anterior and posterior edge, apical papillary tuft. Possible epipodial sense organ (ESO) on ventral base of second epipodial tentacle [or base of broken secondary ramus of epipodial tentacle?]. Opercular attachment (oa) with scale-like muscle fibres. Two mantle tentacles at posterior convergence of mantle slit.

Differential diagnosis. This is the first record of any anatomid from the Peruvian coastline. It differs from T. baxteri from the Pacific Northwest by the turreted shape (lenticular in T. baxteri ), TI of 1 whorl (0.66 in T. baxteri ), and the less distinct axial cords (raised lamellae in T. baxteri ). The comparison is based on examination of the holotype of T. baxteri by SEM, plus conspecific material as identified by comparison to holotype.

Thieleella kelseyi from the Pacific North-West shares the overall trochoid-turreted shape, and the overall sculptural pattern. The difference in TI whorls (0.66 in T. peruviana , 0.75 in T. kelseyi ) is not diagnostic as intraspecific variability is known to be ±0.125 whorls ( Geiger 2003). The overall shell shape is less turreted in T. kelseyi , with the suture being only one width of the selenizone below the selenizone, whereas in T. peruviana that space is up to three times as wide. Although the position of the suture descends with growth, the distinction holds particularly for larger specimens (3 mm). The axials are about twice as dense in T. kelseyi , particularly towards the apertural margin of large specimens (3 mm). Furthermore, the radula shows some striking dissimilarities, particularly in the shape of lateral tooth 5. While it is broad with five denticles on inner margin in T. peruviana , it is more elongated with approximately 12 denticles on the inner margin in T. kelseyi . Although the individual distinctions may each appear slight, in conjunction they allow for a clear separation of the two taxa.

Thieleella bathypacifica n. sp. from deep water west of Central America, has on TI a strong spiral cord in the position of the selenizone where the shell profile shows a distinct angle and has fewer (15 vs. 42) and stronger axial cords on TI, while T. peruviana has only a fine spiral line, does not show an angle in the shell’s profile, and has more (42 vs. 15) and finer axial cords on TI.

Figures

FIGURE 20. Holotype of Thieleella peruviana n. sp. Arrows indicate remnant of protoconch sculpture; most of apical protoconch surface eroded. Scale bar shell = 1 mm. Scale bar protoconch = 100 µm.

FIGURE 21. Anatomy of Thieleella peruviana n. sp. A. Head-foot complex from left side. Scale bar = 1 mm. B. Cephalic tentacle and suboptic tentacle enlarged; note absence of eye or eyestalk. Scale bar = 100 µm. C. Epipodial tentacles with bi-serial papillae on anterior and posterior margin. Box shows enlarged area shown in D. Scale bar = 100 µm. D. Tip of epipodial tentacle with papillae Scale bar = 20 µm. E. Ventral view of epipodial tentacle and potential epipodial sense organ. Scale bar = 100 µm. F. Mantle tentacles at posterior junction of slit. Scale bar = 100 µm. act: accessory cephalic tentacle. ct: cephalic tentacle. ESO: epipodial sense organ. et: epipodial tentacle. oa: opercular attachment site. sn: snout. st: suboptic tentacle. vm: visceral mass.

FIGURE 22. Radula and operculum from holotype of Thieleella peruviana n. sp. A. Overview of entire radula. B. Central field enlarged. D. Series of lateral teeth. D. Operculum. Scale bar A = 100 µm. Scale bars B, C = 10 µm. Scale bar D = 1 mm.