Aforia obesa Pastorino & Sánchez, 2016, new species

Aforia obesa new species.

Figures 4 A–M; figures 5 A–E; figures 6 A–E

Description. Shell large, biconic, fusiform, young shells translucent, adults chalky white in color, up to 34 mm height; protoconch paucispiral, globose, about two whorls (~ 1.45 mm width x 2.08 mm height), irregular oblique spiral wrinkles visible; Anal sinus appears on second whorl of larval shell; transition to teleoconch gradual; teleoconch comprising 5 whorls; anal sinus at the upper third of the spire whorls and above the periphery on the last whorl, with the deepest part forming a slightly raised selenizone on the whorls, which otherwise are gently rounded and lack a keel; suture moderately deep; axial ornamentation of irregularly spaced growth lines all along shell; spiral ornamentation of fine, gently, undulating spiral threads increasing in number, 5 in the first whorl, 8 on second and third whorl, 17 on the fourth and up to 90 on the last whorl below selenizone; above selenizone, 7 in the first whorl, 8 on second and third to 11 on the fourth and fifth whorls; anterior siphonal canal narrow and very long; aperture elliptical.

Operculum oval (juveniles) or oval elongated (adults), with subterminal nucleus, brownish, translucent.

Radula of type 3 “ Turridae ” according to Kantor & Taylor (2000), short, rachidian unicuspid, with curved base, faint secondary denticles at both sides of central cusp, each one showing continuity towards the base, marginal teeth duplex with a flat major element; accessory limb robust, thick, base attached to radular membrane and major element. Penis long and broad, flat with large conical terminal papilla surrounded by a thin collar. Eyes large as in A. goniodes. Table 3 summarizes shell measurements of the new species.

Type material. Holotype, MACN-In 40475, (Figure 4 A–C), Paratypes, MACN-In 40476, 40477, 40478, 40479; MLP-Ma 14176; CNP-Inv 2048.

Type locality. 38°01.631'S, 54°30.275'W in 997 m depth, collected on May 26 2013, St. 41 “ Talud Continental ” expedition of R/V “PUERTO DESEADO”.

Etymology. obesa: fat in Latin, in relation to the thick profile in the last whorl of the shell.

Material examined. All specimens collected on “ Talud Continental ” expedition of R/V “PUERTO DESEADO”: MACN-In 40476, St. 8, 37°57.857´S, 54°57.406´W, in 647 m, 5 SH, 1 SP; MACN-In 40477, St. 10, 37°59.706´S, 54°41.854´W in 852 m, 1 SH, 1 SP; MACN-In 40479, St. 14, 38°0.984´S, 54°30.326´W in 1006 m, 10 SH, 6 SP; MACN-In 40480, St. 43, 37º53.837´S, 54º30.458´W, in 998 m depth, 3 specimens; MACN-In 40478, St. 44, 37°53.557'S, 54°42.941'W in 780 m, 2 SH, 1 SP; MACN-In 40481, St. 59, 37°49.688'S, 54°5.236'W in 1398 m, 2 SH; MLP-Ma 14176, St. 41, 38°01.631'S, 54°30.275'W in 997 m, 3 SH, 4 SP; CNP-Inv 2048, St. 44, 37º53.557´S, 54º42.941´W, in 780 m depth, 2 SP.

continued.

Distribution. Only known from localities around the Mar del Plata Submarine Canyon in 647 to 1,398 m depth.

Remarks. This species can be distinguished from all other Atlantic representatives of Aforia by the lack of a distinct keel, having instead a kind of raised selenizone near the upper one-third of the spire whorls. The spiral ornamentation consists of wavy threads and no microscopic granules were present as in A. goniodes, the only sympatric species. The profile of the shell of A. obesa n. sp. looks similar to A. lepta (Watson, 1881) from New Zealand and A. goodei Dall, 1890 from Chiloe Is., Chile. McLean (1971) considered all deep-water species from the Eastern Pacific as a synonym of A. goodei. Both the latter species are blind (as well as A. persimilis Dall) according to Sysoev and Kantor (1987), a character truly different from the new species here described. In addition, the rachidian tooth has weak denticles at both sides of the unique central cusp, in A. obesa n. sp. a feature, which in fact, separates it from every known species of Aforia. Also, the size of the accessory limb of the marginal tooth is thicker than in A. goniodes.

Antarctic species. A. magnifica and A. multispiralis, both common Antarctic species, were studied for comparative purposes only.