Gastrocopta itaboraiensis, Salvador & Simone, 2013

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

Gastrocopta itaboraiensis sp. nov.

( Figs. 94-96 )

Holotype: MNRJ 5018 -I-B ( Figs. 94-96 ).

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. The precise stratigraphic occurrence can’t be assessed; probably Sequence S1, the same sequence of occurrence of Gastrocopta mezzalirai ( Medeiros & Bergqvist, 1999; Bergqvist et al. 2006).

Etymology: Reference to Itaboraí Basin.

Diagnosis: Shell smooth, oval. Greatest width on penultimate whorl. Aperture rounded (except parietal region), with three small teeth: one parietal, one columellar and one palatal.

Description: Shell diminutive, oval. Greatest width on penultimate whorl; width ~⅔ shell length. Spire angle ~65°.Spire apex not protuberant. Protoconch flattened, blunt, smooth; transition to teleoconch not clear. Shell smooth, except for growth lines. Profile of whorls convex. Suture weakly marked, slightly oblique (diagonal) to columellar axis. Aperture rounded (except parietal region), orthocline; aperture ~⅓ shell length and ~½ width. Peristome reflected, incomplete (absent in parietal region). Aperture with three small teeth: one parietal, one columellar and one palatal; none extending itself towards interior. Body whorl ~⅓ shell length.

Measures (in mm): Holotype: 5 whorls; H = 1.5; D = 1.0; S = 0.9; h = 0.6; d = 0.5; H/D = 1.5; h/d = 1.2.

Examined material: Holotype.

Discussion: G. itaboraiensis has approximately the same size of G. mezzalirai , but it can easily be differentiated by its more oval shell, with the greatest width on its penultimate whorl. G. itaboraiensis has a round- ed aperture with, apparently, three small teeth: one parietal, one columellar and one palatal. However, the bad preservation state (mainly in the apertural region, which is filled by sediments of the same color as the shell) and the species’ diminutive size make clear observation rather difficult, even under the stereomicroscope. Therefore, it is possible that a different number of teeth actually exist and that they are not visible in this condition.

Despite large teeth being commonplace in Gastrocopta , there are many species with smaller ones like, for instance, G. oblonga (Pfeiffer, 1852) and G. pellucida Pilsbry, 1980 . The great differential of G. itaboraiensis is its globular shape, unknown in the genus, despite the North-American G. tappaniana (C.B. Adams, 1842) is near to this shape. Still, a rounded shell is common in some vertiginid genera like Vertigo and Nesopupa Pilsbry, 1900 .

Basommatophora

Family Planorbidae

Subfamily Planorbinae

Genus Biomphalaria Preston, 1910 Biomphalaria itaboraiensis ( Mezzalira, 1946)

( Fig. 97 )

Australorbis itaboraiensis Mezzalira, 1946: 159 (2 figs.); Paula Couto, 1949: 11; Brito, 1967: 13 (pl. 3, fig. 3).

Biomphalaria itaboraiensis : Ferreira & Coelho, 1971: 465; Palma & Brito, 1974: 391 (pl. 1, fig. 8); Simone & Mezzalira, 1994: 49 (pl. 14, fig. 409); Bergqvist et al., 2006: 59 (fig. 72).

Holotype: DGM 3910 -I.

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: Reference to Itaboraí Basin.

Diagnosis: Shell with few whorls. Abrupt increase of width on outer whorls when compared to inner ones.

Re-Description: Shell smooth, planispiral, pseudodextral, with few whorls (from 3½ to 4). Inner whorls narrow, densely packed next to the protoconch; sudden increase of width on outer whorls. Transition to teleoconch unclear. Aperture sub-circular, at same plane as shell; aperture ~2/5 shell width. Umbilicus shallow.

Examined material: DGM 4994 -I (1 specimen) , unnumbered (2 specimens); MNRJ 5041 -I (7 specimens) .

Discussion: Biomphalaria Preston, 1910 is a Recent genus (with other known fossil record; Simone & Mezzalira, 1994), occurring in Africa and the Americas, much studied due to the medicinal importance of some species. The only Biomphalaria from Itaboraí was originally described by Mezzalira (1946) in the genus Australorbis , which was later considered synonym of Biomphalaria by the Opinion 735 of the ICZN (1965). Unfortunately, the holotype of B. itaborahiensis is lost; it could not be found in the museum’s collection (previously DGM, now MCT) and also was not in the records of lent material. Luckily, there is more non-type material available.

B. itaborahiensis displays few whorls: the inner ones are densely packed next to the protoconch, while the outer whorls show an abrupt increase in width. Besides these characters, and the Paleocene age, that can help to differentiate B. itaborahiensis from the other species in the genus, there is not much information to be extract from the shell. The shells of Biomphalaria species are very similar among themselves, displaying few (or none) characters with appreciable interspecific differences; taxonomic studies in the genus are based mainly on anatomical characters ( Baker, 1945; Hubendick, 1955; Paraense, 1975).

Interestingly, the occurrence of a planorbid (basommatophorans) in Itaboraí indicates the presence of a fresh water environment in the basin’s vicinity during the Paleocene (all the other Itaborahian pulmonates are strictly terrestrial stylommatophorans), as already noted by Palma & Brito (1974).

Figures

FIGURES 86-97: 86-87. Eoborus fusiforme sp. nov. (MNRJ 5188-I; holotype); shell length 18.5 mm. 88. ”Brachypodella” britoi (MNRJ 5025-I; paratype); shell length 4 mm. 89-90. “Brachypodella” britoi (MNRJ 5026-I; paratype); shell length (both) 4 mm.91-93. Gastrocopta mezzalirai (MN 5018-I-A; holotype); shell length 1.5 mm. 94-96. Gastrocopta itaboraiensis sp. nov. (MNRJ 5018-I-B; holotype); shell length 1.5 mm. 97. Biomphalaria itaboraiensis (DGM unnumbered); greater width 5 mm.