Brasilennea arethusae Maury, 1935

Salvador, Rodrigo Brincalepe & Simone, Luiz Ricardo Lopes De, 2013, Taxonomic Revision Of The Fossil Pulmonate Mollusks Of Itaboraí Basin (Paleocene), Brazil, Papéis Avulsos de Zoologia 53 (2), pp. 5-46 : 5-46

Brasilennea arethusae Maury, 1935

( Figs. 3-16 )

Brasilennea arethusae Maury, 1935: 4 (figs. 1-5); Oliveira, 1936: 4; Mezzalira, 1946: 18; Paula Couto, 1949: 11; Magalhães & Mezzalira, 1953: 221 (pl. 64, fig. 262, 262°); Trindade, 1956: 15 (pl. 3, figs. 1c, 2c); Zilch in Wenz, 1959-60: 578 (fig. 2025); Brito, 1967: 18 (pl. 3, fig. 6); Jaeckel, 1969: 822; Parodiz, 1969: 186 (pl. 19, figs. 3, 12); Palma & Brito, 1974: 396 (pl. 1, fig. 9); Simone & Mezzalira, 1994: 51 (pl. 15, fig. 430); Bergqvist et al., 2006: 59 (fig. 74); Salvador et al., 2011: 445 (fig. 1A-G, L); Salvador & Simone, 2012: 2 (figs. 5-6).

Strobilops mauryae Ferreira & Coelho, 1971: 469 (fig. 6); Palma & Brito, 1974: 397.

Strobilopsis mauryae : Simone & Mezzalira, 1994: 49 (pl. 14, fig. 413); Bergqvist et al., 2006: 60 (fig. 76). (Error)

Holotype: AMNH 24237 (examined; Figs. 10-11 ).

Paratypes: AMNH 24238 (1 specimen, examined; Fig. 12 ), 24239 (1 specimen, examined; Fig. 16 ) .

Type Locality: Limestones of Parque Paleontológico de São José de Itaboraí, Rio de Janeiro, Brazil. Park’s center coordinates: 22°50’20”S, 42°52’30”W .

Geographic and stratigraphic occurrence: Known only from the type locality: Sequence S1 ( Medeiros & Bergqvist, 1999; Bergqvist et al., 2006).

Age : Tertiary, Middle Paleocene.

Etymology: Due to the terrestrial habits of the species, Maury (1935) dedicated it to Arethusa (sometimes also spelled Arethousa), a nymph from Greek mythology. There are mentions to two nymphs of such name in the myths: one is a Nereid (or even a goddess of springs) while the other is one of the Hesperides ( Kerényi, 1951). Maury did not specify which one she was referring to, stating only that it was a “sylvan nymph”. Thus, the name probably refers to the latter since the previous is a water-related being.

Diagnosis: Shell bigger than other species. Greatest width in central portion of shell. Sculptured by stronger whorls, usually in lesser quantity. In some specimens, weaker ribs, in greater quantity (similar to the other Brasilennea species), may also occur in some specimens.

Re-Description: Shell medium-sized, multispiral, pupiform, with acuminated apex. Greatest width in central portion of shell; diameter ~½ shell length. Spire angle ~45°. Protoconch dome-shaped, blunt, smooth; transition to teleoconch clear. Columella hollow (at least on first whorls). Profile of whorls flat. Suture well-marked, linear, practically perpendicular (horizontal) to columellar axis, becoming more oblique towards last whorls. Sculptured by strong, raised and well-marked ribs, regularly distributed, becoming less oblique towards last whorls, and usually in lesser quantity than other Brasilennea species (~35 on penultimate whorl). Body whorl with two well-marked and deeply set spiral furrows, one central and the other basal, placed equidistantly from upper furrow and shell bottom. Aperture large, orthocline, approximately semicircular (parietal and columellar lips straight, others rounded); ~⅓ shell length. Peristome complete, well-marked, with duplicated aspect (parallel lamella sensu Maury, 1935). Single and strong median parietal lamella, reaching peristome and extending itself towards interior up to ~¼ of body whorl. Columellar spiral lamella extending itself towards shell’s interior. Body whorl ~2/5 shell length. Umbilicus narrow.

Measures (in mm): Holotype: 11 whorls; H = 23.6; D = 13.2; S = 15.9; h = 7.5; d = 6.1. Paratypes: AMNH 24238 : 11 whorls; D = 12.6; S = 15.8 . AMNH 24239 (juvenile): 6 or 7 whorls (shell apex covered by sediment); H = 4.1; D = 7.7; S = 1.8; d = 3.2. Mean (n = 35): 11 whorls (eventually 10); H = 21.6 ± 2.2 (max 24.9; min 17.3); D = 11.6 ± 1.2 (max 14.4; min 9.4); S = 14.9 ± 1.7; h = 6.9 ± 0.9 (max 7.8; min 5.2); d = 5.5 ± 1.0 (max 6.9; min 3.2) .

Examined material: Types. DGM 4222 -I (1 specimen) , 4998-I (8 specimens), 5002-I (25 specimens), unnumbered (7 specimens); MNRJ 3346 -I (2 specimens) , 3348-I (2 specimens), 4338-I (5 specimens); MZSP 86321 (20 specimens) , 86322 (1 specimens), 86324 (4 specimens). Type material of Strobilops mauryae : MNRJ 5020 -I (holotype), 5021-I (paratype, 4 specimens) .

Discussion: B. arethusae is the type species of the genus by original designation and monotypy ( Maury, 1935). It is larger than the other species, presenting usually 11 whorls, though a few specimens have 10 whorls. A single specimen has 9 whorls ( Fig. 13 ), but it seems to be anomalous, since it also shows a slightly different shell shape, with the lip largely reflected and without the doubled aspect, and does not have the parietal lamella. The shell shape can vary slightly in the last whorls, which can be thinner and present the aperture more centrally located (notably in the holotype, Figs. 10-11 ). In the same manner, the ribs in some specimens (~40%) can be weaker and more abundant ( Figs. 10-12 ), like those of other Brasilennea species.

B. arethusae usually has stronger ribs (and fewer per whorl) than other Brasilennea species. Quensen & Woodruff (1997) attribute such strong ribs to protection against predators in Cerion Röding, 1798 ; the ribs strengthen the shell structure and make it harder for predators (in this case, crabs) to crush it. However, B. arethusae ’s possible predators are unknown: there is no record of crabs in Itaboraí or other possible predators known for crushing shells, such as beetles ( Symondson, 2004); still, some small mammals, also potential predators ( Allen, 2004), do occur in Itaboraí, but possibly not in the same sequence as the Brasilennea ( Bergqvist et al., 2006) . In any case, the shell of B. arethusae would be more resistant to predation due to its strong ribs.

Ferreira & Coelho (1971) described Strobilops mauryae ( Figs. 14-15 ), stating that it could be taken for fragments of B. arethusae and also that Maury (1935) had committed such error when defining the paratype of B. arethusae ( AMNH, 24239; Fig. 16 ) as a juvenile. Ferreira & Coelho (1971) gave the key character to place their specimens in the genus Strobilops Pilsbry, 1893 : a tooth (or “well-developed basal fold”) in the aperture’s basal region. Teeth and lamellae are typical of the family Strobilopsidae , which, for many authors, contain only the genus Strobilops , and are essential to the family’s taxonomy ( Schileyko, 1998a). In the illustration of S. mauryae presented by Ferreira & Coelho (1971: 469, fig. 6), such tooth can be clearly seen. However, examining the type material, we saw that only the holotype ( Figs. 14-15 ) presented such tooth. Further examination revealed that the supposed tooth was in fact a grain of sediment attached to the shell.

Therefore, here we propose that the specimens previously classified as S. mauryae are in fact juveniles of B. arethusae (or fragments of it, namely the top of the spire). Besides all the characters of the supposed specimens of S. mauryae being identical to what is found in the top region of the shell of B. arethusae (like sculpture pattern, aperture shape, umbilicus shape, absence of teeth and lamellae etc.), they do not present a single character that could allow their classification as strobilopsids, such as long parietal lamellae, greatly extending themselves towards the shell’s interior, and a thickened and reflected lip ( Schileyko, 1998a). Moreover, no deflection of the peristome was detected in the specimens identifiable as S. mauryae , another necessary character for confirming the generic attribution.

Figures

FIGURES 3-9: Brasilennea arethusae (MZSP 86322); shell length 21 mm. 3-5. Overview. 6. Body whorl, showing the two spiral furrows. 7. Smooth protoconch. 8. Aperture; peristome with duplicate aspect (parallel lamella sensu Maury, 1935). 9. Broken aperture, showing the parietal (pt) and columellar (cl) lamellae.

FIGURES 10-19: 10-11. Brasilennea arethusae (AMNH 24237; holotype); shell length 23.5 mm. 12. B. arethusae (AMNH 24238; paratype); shell length 24 mm. 13. Anomalous specimen of B. arethusae (DGM 4998-I); shell length 27 mm. 14-15. ”Strobilopsis mauryae” (MNRJ 5020-I; holotype); greater width 4.5 mm. 16. B. arethusae (AMNH 24239; paratype); greater width 7.5 mm. 17-19. Brasilennea guttula (MCT 6940-I; holotype); shell length 13.5 mm.