Cortana, 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

Cortana gen. nov.

( Figs. 40-42 )

Type species: Bulimulus carvalhoi Brito, 1967 .

Included species: Cortana carvalhoi ( Brito, 1967) .

Geographic and stratigraphic occurrence: Known only from Itaboraí Basin, limestone Sequence S1 ( Medeiros & Bergqvist, 1999; Bergqvist et al., 2006).

Age : Tertiary, Middle Paleocene.

Etymology: The name was taken from a character of the science fiction franchise “Halo”, and alludes to the convoluted markings on the shell surface of the holotype of Cortana carvalhoi . Grammatical gender: feminine.

Diagnosis: Shell fusiform. Spire apex acuminated, with straight outline. Profile of whorls flat. Peristome greatly reflected, with exception of upper palatal region. Aperture oval, elongated anteroposteriorly, orthocline; median palatal tooth, columellar lamella and channel-like structure immediately above the lamella. Umbilicus imperforated.

Description: Shell dexterous, fusiform. Greatest width on body whorl. Spire apex acuminated, with straight outline. Profile of whorls flat. Suture well-marked, linear, oblique (diagonal) to columellar axis, Protoconch apparently smooth; transition to teleoconch unclear. Teleoconch smooth, except for growth lines. Aperture medium-sized, oval elongated anteroposteriorly, orthocline, occluded by a columellar lamella and palatal tooth in its median portion. Peristome greatly reflected, with exception of upper palatal region; incomplete (absent in parietal region). Aperture with a columellar lamella extending itself towards the shell interior and a median palatal tooth. Aperture with channel-like structure immediately above the columellar lamella, giving the impression of a twisted columella. Umbilicus imperforated.

Discussion: The species originally described as Bulimulus carvalhoi , is here transferred to a new genus because there is not an existing genus, fossil or recent, which can unequivocally house it. The new genus Cortana is based on its fusiform shell and the many characters of the shell aperture.

Shell shape: Despite the overall shell shape being typical of some genera of Orthalicidae , a shell as markedly fusiform as in the Itaborahian species, with the body whorl greatly thinning towards the shell’s bottom, clearly does not occur in the genus Bulimulus . There are other fusiform genera, especially in the subfamily Odontostominae , but none of them has such a large body whorl, typical of Bulimulinae . As such, Cortana is most similar to the South-American bulimuline genus Eudolichotis Pilsbry, 1896 , which is both fusiform and has a large body whorl.

Aperture, peristome and lamellae: The great differential in Cortana is in its aperture; there is nothing similar to it in any other orthalicid, recent or fossil. The peristome is greatly reflected in the lower half of the aperture, which is U-shaped; this region is delimited by a strong columellar lamella and a median palatal tooth. Besides, immediately above the lamella, there is a channel-like structure, which gives the impression of a twisted columella.

Cortana carvalhoi was already classified as Itaborahia ( Bergqvist et al., 2006) due to its “columellar fold”. However, the lamella of C. carvalhoi is much stronger and is located in a much lower position than in Itaborahia . This, when taken together with the fusiform shape of the shell, its straight spire, orthocline aperture and the channel-like structure, indicates clearly that Cortana carvalhoi cannot be allocated in the genus Itaborahia .

C. carvalhoi also shows similarities to the genus Eudolichotis regarding its aperture. Besides the similar shape, Eudolichotis has a strong columellar lamella and the peristome usually reflected. Moreover, some species as, for example, E. distorta (Bruguière, 1789) , also have a thickening of the median palatal region. This thickening, however, does not form a proper tooth. Nevertheless, besides having a palatal tooth, C. carvalhoi also differentiates itself from Eudolichotis by the channel-like structure above the columellar lamella and by the upper palatal region of the peristome (above the tooth), which is not reflected. Another genus in which a similar configuration of the aperture is present is Otostomus Beck, 1837 , from the east-central region of Brazil ( Simone, 2006). This genus had two species, recently put in synonymy ( Simone, 2006). The aperture of Otostomus signatus (Spix, 1827) shows a large parietal lamella and a parallel lamella extending itself from the basal region to the superior palatal region. Still, the shape of the aperture of O. signatus , as well as its shell shape and the presence of an umbilicus, makes it very different from Cortana .

Figures

FIGURES 32-42: 32-33. Temesa magalhaesi (DGM 4997-I) with broken aperture, showing the parietal lamella (pt). 34-35. Cecilioides sommeri (MNRJ 5016-I; holotype); shell length 2.5 mm. 36. Bulimulus fazendicus (AMNH 24243; holotype); shell length 16.5 mm. 37. B. fazendicus (AMNH 24242; paratype); shell length 16.5 mm. 38-39. Bulimulus trindadeae (MNRJ 5022-I; holotype); shell length 9.5 mm. 40-42. Cortana carvalhoi (DGM 4995-I; holotype); shell length 30.5 mm.