Anachis rechonchuda, Lima, Silvio Felipe Barbosa & Guimarães, Carmen Regina Parisotto, 2015

Lima, Silvio Felipe Barbosa & Guimarães, Carmen Regina Parisotto, 2015, New bathyal Anachis (Neogastropoda: Buccinoidea: Columbellidae) from the Southwestern Atlantic, and the designation of a lectotype for A. stricta (Watson, 1882), Zootaxa 3949 (3), pp. 445-450 : 446-449

Anachis rechonchuda n. sp.

( Figs 1 A–G, 2A; Table 1 )

Type material. Holotype, MNRJ 26.718; paratypes: 1 shell, ANSP 450482; 2 shells, BMSM 17938; 4 shells, CMPHRM-A 4429; 2 shells, IBUFRJ 19468; 5 shells, IBUFRJ 19469; 2 shells, UF 456794; 2 shells, UFPB MOLL 3537; 5 shells, UFS_MOL; 2 shells, MNHN IM- 2012-33; 5 shells, MNRJ 17286; 2 shells, MORG 50926; 5 shells, MZSP 108841; 5 shells, NHMUK 20090251; 5 shells, ZUEC GAS 623 ( Table 1 ), Brazil, Pernambuco State, continental slope (REVIZEE/NE: 08°46.5'00''S, 34°44.5'00''W, 690 m, 18.xi.2000, 'Natureza').

Type locality. Brazil, off the state of Pernambuco (08°46.5'00''S, 34°44.5'00''W, 690 m depth).

Geographic distribution. Known only from the type locality.

Description. Shell small (TL 3.93–4.68 mm; SW 2.02–2.42 mm), stout, broadly biconic, glassy, shining, smooth, translucent white ( Fig. 1 A–B, 2A). Protoconch (PD 0.42–0.50 mm; PH 0.40–0.72 mm) white, glassy, glossy, smooth, blunt, dome-shaped ( Fig. 1 F–G), with 1.50 to 1.75 whorls ( Fig. 1 E); transition to teleoconch abrupt marked by strong opisthocline axial edge ( Fig. 1 G). Spire conical, blunt, low (SL 1.25–1.70 mm), about 1/3 of shell length ( Fig. 1 A–B, 2A). Teleoconch with three to about 4.25 stout, moderately convex whorls ( Fig. 1 A–B, 2A); surface covered by obscure axial growth striae ( Fig. 1 C–D, G). Axial sculpture consisting of rounded, regularly convex, slightly prosocline to orthocline ribs that extend from suture to suture (not continuous between whorls) ( Fig. 1 A–B), obsolete and narrowly spaced on first teleoconch whorl ( Fig. 1 A–B, E–G), increasing in strength towards next whorls ( Fig. 1 A–B) and becoming strong, raised, and widely spaced on penultimate and last whorl ( Fig. 1 A–B). Spiral sculpture consisting of weak subsutural cord on teleoconch whorls, more pronounced on penultimate and last whorl ( Fig. 1 A–B, E). Intersection of ribs and cord give strongly wavy outline to suture, forming small, rounded subsutural tubercles, more pronounced on penultimate and last whorl ( Fig. 1 A–B, 2A). Subsutural tubercles projecting a minute shoulder, slightly below suture ( Fig. 1 A–B, E, 2A). Axial interspaces slightly concave, about one to two times rib width on first and second teleoconch whorl and about two to three times rib width on penultimate and last whorl ( Fig. 1 A–B, 2A). Suture incised, deep, channeled, angulated by projection of tubercles ( Fig. 1 A–B, E–G, 2A). First teleoconch whorl with indistinct riblets or sculptured with 14 to 28 riblets gradually increasing in strength ( Fig.1 E–G); second whorl sculptured with 14 to 25 riblets/ribs; penultimate whorl sculptured with 12 to 17 ribs ( Fig. 1 A–B, 2A); last whorl (LW 2.76–3.24 mm) broad, inflated, globose, about 65 to 70% of shell length, sculptured with about 13 ribs ( Fig. 1 A–B, 2A) that evanesce toward siphonal canal ( Fig. 1 C–D). Base imperforate, strongly conical, very contracted ( Fig. 1 C–D). Aperture (AL 1.80–2.20 mm) trapezoidal, enlarged above, about 1/3 of shell length ( Fig. 1 A, C, 2A). Parietal region straight, smooth, glazed ( Fig. 1 A, C, 2A). Outer lip simple, thin, very slightly curved, smooth within ( Fig. 1 A, 2A). Inner lip thin, smooth, glazed, very slightly curved, weakly reflected on siphonal canal and parietal region ( Fig. 1 A, C, 2A). Anal notch narrow, shallow ( Fig. 1 A, 2A). Siphonal canal short, open, slightly deflected on dorsal region, ornamented by indistinct or six to 10 weak/ strong spiral threads ( Fig. 1 A–D, 2A).

Etymology. The specific name is an adjective in Portuguese ( rechonchuda = chubby, with rounded shape), referring to the inflated, stout, swollen aspect of the teleoconch whorls, especially last whorl.

Comparison. The new species and the West African Anachis chuni (Thiele, 1925) and A. delemarrei Rolán & Boyer, 2006 have a similar pattern of axial ornamentation and subsutural spiral cord forming nodules below the suture.

In Anachis rechonchuda n. sp., the intersection of ribs and cord give a strongly wavy outline to suture, the base is smooth (except for the presence of spiral threads on the siphonal canal), the outer lip is very slightly curved, and the siphonal canal is short. Anachis chuni has a slightly wavy outline to suture, a base entirely ornamented by thin spiral threads, a well arched outer lip, and a moderately projected siphonal canal ( Thorsson & Monsecour 2008: 3, lectotype ZMB). Anachis rechonchuda n. sp. differs from A. delemarrei in having a biconic shell (larger size: TL 3.93–4.68 mm), a trapezoidal aperture and a thin, smooth outer and inner lip. Rolán & Boyer (2006: 25, figs. 1–6) characterized A. delemarrei by the presence of a broadly fusiform shell (up to 3.5 mm long), a narrow and elongated aperture, small denticles on the columellar border, and a slightly thickened outer lip. Furthermore, A. rechonchuda n. sp. has a blunt, a dome-shaped protoconch (up to 1.75 whorls) while A. delemarrei has a sharply pointed protoconch (with 2.25 whorls).

Anachis rechonchuda n. sp. resembles A. strix by the presence of a strongly biconic shell, dome-shaped protoconch, and slightly convex teleoconch whorls. These species have also strong, rounded, widely spaced axial ribs, and a slight subsutural cord forming small tubercles and projecting a minute shoulder at the intersection of both sculptures. The new species differs considerably from A. strix based on a number of characters. Anachis rechonchuda n. sp. has a small, low, conical shell up to 4.68 mm long and with about 4.25 teleoconch whorls, while A. strix ( Fig. 2 C) has a rather slender shell 7 to 9 mm long and with five to eight teleoconch whorls. Although this species has a broad, inflated last whorl, Anachis rechonchuda n. sp. exhibits the proportionally largest body whorl, measuring approximately 65% of the shell length, and a low spire (about 1/3 of the shell length). In contrast, A. strix ( Fig. 2 C) the last whorl and a higher spire each account for about 1/2 of the shell length. The new species has a more pronounced projection of the tubercles on the subsutural region, which give a strongly wavy outline to the suture. In contrast, there is a slight projection of the tubercles and consequently a slightly wavy outline to the suture in A. strix ( Fig. 2 C). Furthermore, A. rechonchuda n. sp. exhibits a smooth outer lip, while A. strix ( Fig. 2 C) usually has one denticle on the outer lip ( Costa 2005).

Anachis strix was originally described and figured by Watson (1886: 237–238, pl. 13, fig. 2) from specimens collected from deep waters off the West Indies and northeastern Brazil (syntype NHMUK 1887.2.9.818— Fig. 2 C, continental slope off the state of Alagoas, 09°05'S, 34°50'W—Fig. 2C). Specimens of A. strix were collected on the continental slope off the state of Pernambuco during the REVIZEE/Score-Northeast Program (2000), thereby improving our knowledge of its conchology ( Costa 2005; Rios 2009).

Anachis rechonchuda n. sp. most closely resembles A. stricta from the West Indies. Both species have a stout shell with a similar outline and rounded, smooth protoconch (dome-shaped with 1.5 whorls). Anachis rechonchuda n. sp. and A. stricta also share a blunt spire with slightly convex whorls and a broad, tumid last whorl with a very contracted base. Furthermore, these species exhibit a slight subsutural cord, the intersection of which with the ribs projects little tubercles and a minute shoulder. The new species differs in having up to about 4.25 teleoconch whorls, while the teleoconch of A. stricta ( Fig. 2 B) develops up to six whorls. The inner lip is slightly concave, and the outer lip is smooth in A. rechonchuda n. sp. However, A. stricta has a straight inner lip and about 10 small denticles on the outer lip ( Fig. 2 B). The spiral sculpture on the new species consists of a weak subsutural cord and spiral threads on the siphonal canal. Anachis stricta ( Fig. 2 B) is spirally sculptured by two well-marked subsutural furrows interrupted by ribs, broad, flat but obsolete threads on the spire, and very distinct threads on the base ( Watson 1886: 238; pl. 13, fig. 3). Finally, A. rechonchuda n. sp. differs from A. stricta by the presence of a more pronounced projection of the small tubercles in the subsutural region.

Anachis stricta was described on the basis of two adult specimens dredged from deep waters off the West Indies (North of Culebra Island, St. Thomas, 18°38'30''N, 65°05'30''W, at a depth of 713 m) ( Watson 1886: 238). The syntype of A. stricta figured herein ( Fig. 2 B) is in good condition and was chosen as the lectotype (NHMUK 1887.2.9.82H-5) under the provisions of Article 74.1 (ICZN 1999). The paralectotype has a worn surface, broken protoconch and outer lip as well as two holes in the ventral region.

Figures

FIGURE 1. Anachis rechonchuda n. sp. (SEM: A, C. holotype; B, D – G. paratypes, IBUFRJ 19468): A. ventral view, B. lateral view, C. view of aperture, D. view of siphonal canal, E – G. view of protoconch. Scale bars: A – B. 500 µm, C – D and E. 200 µm, F – G. 100 µm.

FIGURE 2. Three deep sea Anachis from the Western Atlantic (ventral view): A. Anachis rechonchuda n. sp. (holotype), B. Anachis stricta (lectotype—here designated), C. Anachis strix (syntype—TL 9.80 mm). Scale bars: A. 500 µm, B. 1 mm.

Tables

TABLE 1. Linear measurements (mm) of Anachis rechonchuda n. sp. specimens (N: number, R: range, M: mean; SD: standard deviation).

Anachis rechonchuda n. sp.	N	R	M	SD
Aperture length (AL)	25	1.80–2.20	1.96	0.10
Last whorl length (LW)	25	2.76–3.24	2.91	0.12
Protoconch diameter (PD)	25	0.42–0.50	0.47	0.02
Protoconch height (PH)	25	0.40–0.72	0.46	0.05
Spire length (SL)	25	1.25–1.70	1.50	0.10
Shell width (SW)	25	2.02–2.42	2.21	0.09
Total length (TL)	25	3.93–4.68	4.29	0.22