Rapturella atlas,

Cunha, Carlo M. & Simone, Luiz Ricardo L., 2018, A new species of the genus Rapturella (Gastropoda: Acteonidae) from southeast Brazil, Zootaxa 4521 (1), pp. 125-128: 125-126

publication ID

https://doi.org/10.11646/zootaxa.4521.1.7

publication LSID

lsid:zoobank.org:pub:13AD67F2-D182-47F5-8664-5BF46B6102B0

persistent identifier

http://treatment.plazi.org/id/B53DED70-F324-4F4A-9B87-0CB1D59D38FF

taxon LSID

lsid:zoobank.org:act:B53DED70-F324-4F4A-9B87-0CB1D59D38FF

treatment provided by

Plazi

scientific name

Rapturella atlas
status

n. sp.

Rapturella atlas  n. sp. ( Figure 1View FIGURE 1)

Type material. Holotype MZSP 91018View Materials ( Fig. 1View FIGURE 1 A–B)  . Paratypes: BRAZIL, Rio de Janeiro state, Cape São Tomé, 21°58.32' S 40°02.05' W, 155 m, MZSP 107499View Materials, 1View Materials shell (18.vi.2005); São Paulo state, São Sebastião , 24°44'69" S 44°44'965" W, 153 m, MZSP 107496View Materials ( Fig. 1View FIGURE 1 C–F), 1 shell, MZSP 107497View Materials, 1View Materials shell, MNHN 25271View Materials, 2View Materials shells, MNRJ 30855View Materials, 2View Materials shells; 24°42.8' S 44°42.9' W, 162 m, MZSP 107498View Materials, 2View Materials shells (20.xi.1997); 25°14.4' S 45°03.1' W, 147 m, MZSP 107500View Materials, 4View Materials shells (21.xi.1997)GoogleMaps  .

Type locality. BRAZIL: Rio de Janeiro, off Cape São Tomé , 22°00.708' S 40°03.380' W, 162 m (Project Frade Development, sta BC_A_E39_1, C.H. Caetano coll., 29.vi.2005)GoogleMaps  .

Etymology. In honors of Atlas, the nick name of Frank Fontaine, the character of the science-fiction video game series BioShock: an allusion to the hidden identity of the species. The noun in apposition.

Diagnosis. Small shell with walls strongly thickened. Umbilicus deep and narrow. Spiral grooves on teleoconch separated by regularly spaced intervals, each interval about 10 times wider than the grooves; last whorl has about 11 spiral grooves, but no subsutural grooves. Palatal region has no thickened area.

Description. Shell oval, profile rounded, maximum length (L) 3.1 mm; about 1.3 times longer than wide. Walls thickened. Color white; spire short, length about 1/4 of total length ( Fig. 1A, BView FIGURE 1). Protoconch small, glossy, 1 whorl; width about 0.4 mm; separated from teleoconch by narrow orthocline furrow ( Fig. 1FView FIGURE 1: arrows). Teleoconch up to 4 whorls, each whorl convex ( Fig. 1CView FIGURE 1). Surface smooth, glossy, sculptured with narrow punctuated spiral grooves distributed on entire teleoconch; punctuations very small, oval ( Fig. 1DView FIGURE 1); grooves regularly spaced, separated by gaps about 10 times wider than grooves; last whorl with about 11 spiral grooves, gradually becoming deeper and closer to each other towards umbilical area; 3 grooves on anterior half and 8 on posterior half; umbilicus rimate, partially covered by extension of columellar margin. Aperture about 2/3 of total length, antero-posteriorly elongated, length about 1.5 times width; posterior end pointed, anterior (siphonal) rounded. Inner lip concave; superior half convex, rounded, with thin callus, about 1.3 times length of inferior half; inferior half slightly concave, with shallow edge, and small thickened columellar fold in posterior region. Outer lip thick, with sharp edge.

Measurements (length by width in mm). Holotype: 2.8 by 1.6 ( Fig. 1View FIGURE 1 A–B). Paratypes: MZSP 107496 ( Fig. 1View FIGURE 1 C–F), 1 shell, 3.1 by 2.2; MZSP 107497, 1 shell, 2.6 by 1.7; MZSP 107498, 1 shell, 2.7 by 1.8; MZSP 107500, 3 shells, (#1) 2.3 by 1.5, (#2) 1.7 by 1.3, (#3) 2.3 by 1.6; MZSP 138843, 1 shell, 2.7 by 1.8; MNHN 25271, 2 shells, (#1), 2.0 by 1.4, (#2) 2.5 by 1.7; MNRJ 30855, 2 shells, (#1) 1.8 by 1.3; (#2) 2.5 by 1.7; MZSP 90698, 1 shell, 3.3 by 2.2; MZSP 91018, 1 shell, 2.6 by 1.7.

Distribution. Rio de Janeiro to São Paulo, Brazil.

Habitat. Muddy sand bottom, 147–162 m depth.

Material Examined. Types.

Remarks. Rapturella atlas  n. sp. fits in the genus Rapturella  because it presents most of the diagnostic features of the genus including a minute shell size with thick walls, rounded spire whorls with a subsutural shelf, a teleoconch sculptured by spiral grooves composed of rounded punctae, and the characteristic aperture with a rounded trapezoidal shape, a columellar region thickened with a weak fold, a narrow anal canal, and a rounded siphonal canal region.

Rapturella atlas  n. sp. most resembles R. ryani  , from the Florida Keys, USA. It differs by having a smaller size (length up to 2.5 mm, while R. ryani  easily reaches 4 mm); thicker walls forming a more solid shell; 3 spiral grooves on the penultimate whorl (5 more closely spaced grooves on R. ryani  ), about 3 grooves in the periumbilical region (about 10 more closely spaced grooves on R. ryani  ), and a smaller protoconch (0.42 mm, against 0.47 mm of R. ryani  ). Despite it being a smaller species, the smaller protoconch of R. atlas  is a relevant developmental parameter. Rapturella atlas  n. sp. differs from R. globulina (Forbes, 1884)  , from the Eastern Atlantic ( Salvador & Cunha, 2016), by its slightly rounded whorls forming a straighter profile (whorls of R. globulina  are more rounded), the small subsutural shoulder on each whorl (absent on R. globulina  ), and by the more widely spaced spiral grooves on its shell surface. Additionally, R. atlas  n. sp. differs from its congeners in lacking two closely spaced, punctate, subsutural grooves ( Salvador & Cunha 2016: fig. 4C, F), and in lacking a faint tooth-like thickening on the palatal region.

This discovery expands the geographic distribution of the genus Rapturella  southwards to the southwest Atlantic region off the Brazilian coast. However, the distribution of the genus remains restricted, like that of the genera Callostracon Repetto & Bianco, 2012  and Mysouffa Marcus, 1974  , to the Atlantic and Mediterranean. This conforms to the heterogenic distribution of acteonids, with most genera confined to specific regions such as the subarctic (e.g. Neactaeonina Thiele, 1912  ), the Pacific (e.g. Pseudactaeon Thiele, 1925  and Maxacteon Rudman, 1971  ) or the Western Atlantic (e.g. Ovulactaeon Dall, 1889  ). Only the genus Acteon  has a more widespread range, but, with species of such diverse shell shapes (e.g. Rudman 1971; Marcus 1974; Valdés 2008), further taxonomic investigation may result in its segregation into more genera.

The new species, as well as the genus Rapturella  , are recognized only by a combination of few conchological characters. The lack of soft tissue samples inhibits any comparative morphological evaluations or molecular analyses. Thus, the putative relationships of the genus with other acteonids and the classification of the species, which we here assign to Rapturella  , need to be tested once new quality samples become available.

Kingdom

Animalia

Phylum

Mollusca

Class

Gastropoda

Order

Heterostropha

Family

Acteonidae

Genus

Rapturella

Loc

Rapturella atlas

Cunha, Carlo M. & Simone, Luiz Ricardo L. 2018
2018
Loc

Rapturella atlas

Cunha & Simone 2018
2018
Loc

R. atlas

Cunha & Simone 2018
2018
Loc

Rapturella atlas

Cunha & Simone 2018
2018
Loc

R. atlas

Cunha & Simone 2018
2018
Loc

R. ryani

Salvador & Cunha 2016
2016
Loc

R. ryani

Salvador & Cunha 2016
2016
Loc

R. ryani

Salvador & Cunha 2016
2016
Loc

R. ryani

Salvador & Cunha 2016
2016
Loc

R. ryani

Salvador & Cunha 2016
2016
Loc

Rapturella

Salvador & Cunha 2016
2016
Loc

Callostracon

Repetto & Bianco 2012
2012
Loc

Mysouffa

Marcus 1974
1974
Loc

Maxacteon

Rudman 1971
1971
Loc

Pseudactaeon

Thiele 1925
1925
Loc

Neactaeonina

Thiele 1912
1912
Loc

Ovulactaeon

Dall 1889
1889
Loc

R. globulina

Forbes 1884
1884
Loc

Acteon

Montfort 1810
1810