Thaumastus taunaisii
Creators: name: Fernandes, Maurício Romulo
name: Alexandre, Guilherme de Lima
name: Salgueiro, Fabiano
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Stylommatophora
Megaspiridae
Thaumastus
Thaumastus taunaisii

description: Thaumastus cf. taunaisii (Férussac, 1822)
(Figures 7–9, 14)
Records in PNM da Cidade sta. 2, 5 April 2022 [2 sh, MNRJ 23833]; sta. 5, 5 May 2022 [1 spm, MNRJ 22772]; sta. 2, 14 May 2022 [1 sh]; sta. 5, 14 May 2022 [2 sh]; sta. 6, 14 May 2022 [1 spm, MNRJ 22782]; sta. 2, 19 May 2022 [1 sh and 1 spm, with spawning]; sta. 2, 13 August 2022 [6 spm, of which 1 sampled, MNRJ 22886]; sta. 5, 13 August 2022 [1 spm]; sta. 6+, 13 August 2022 [2 spm]; sta. 9, 13 August 2022 [3 spm]; sta. 10, 13 August 2022 [1 sh]; sta. 2, 10 September 2022 [5 spm]; sta. 5, 10 September 2022 [1 sh]; sta. 6, 10 September 2022 [2 spm]; sta. 2, 5 November 2022 [19 spm]; sta. 5, 5 November 2022 [8 spm]; sta. 6, 5 November 2022 [1 spm]; sta. 9, 5 November 2022 [10 spm]; sta. 10, 5 November 2022 [1 spm]; sta. 12, 5 November 2022 [1 spm]; sta. 13, 5 November 2022 [15 spm]; sta. 16, 5 November 2022 [1 spm]; sta. 2+, 22 December 2022 [2 spm]; sta. 6, 22 December 2022 [2 spm]; sta. 22, 22 December 2022 [2 spm]; sta. 23, 22 December 2022 [1 spm]; sta. 24, 22 December 2022 [1 sh]; sta. 13, 13 May 2023 [2 spm, MNRJ 36789]; sta. 2, 17 September 2023 [32 spm]; sta. 5, 17 September 2023 [4 sh, of which 1 sampled, MNRJ 36403]; sta. 22, 17 September 2023 [10 spm].
Description of jaw (MNRJ 22772)
Jaw curve, 2.4 mm long (if stretched), with 12 plates, each nearly rectangular but with varying width (123–321 µm); several (~30) longitudinal micro-spiral threads along the entire extension of the jaw, covering plates and the spaces between them.
Description of radula (MNRJ 22772)
Formula 32-1-32; central tooth narrow, pointed, up to 87 µm long, with a main, nearly rounded cusp projecting over the U-shaped base, which has two distal points of contact with the main cusp that can be interpreted as secondary cusps; lateral/marginal teeth decreasing in size from the innermost teeth L1 (up to 97 µm long) to L12 (up to 81 µm long) and L30–L32 (up to 44 µm long); innermost lateral teeth with a wide base and a major, triangular cusp bordered by two small cusps, the one proximal to the central tooth (cusp 1) extremely reduced, almost indistinct, and the one distal to the central tooth (cusp 3) a small protuberance; outermost teeth gradually have a narrowed base and a considerable reduction of cusp 2’s length, with last teeth (L30–L32) assuming a trapezoidal shape.
Remarks
This species was by far the most common gastropod found in PNM da Cidade, mainly in winter/spring (Supplementary material 3). Its taxonomic identification requires caution due to the historical confusion with and strong resemblance to Thaumastus magnificus (Grateloup, 1840), supposedly differentiated by slight features of the shell and reproductive system (Barros et al. 1991). Some anatomical features of the dissected specimens are more similar to those of T. taunaisii, such as the reduced number of jaw plates (12 in specimens from PNM da Cidade vs 15 in T. magnificus and 10–11 in T. cf. taunaisii; Barros et al. 1991) and the presence of seven groups of ovarian follicles (Figure 9) vs five groups in T. magnificus (Barros et al. 1991). In contrast, other (subjective) anatomical features are closer to those of T. magnificus, such as: reduced fertilisation complex; strong constriction in the middle portion of the spermathecal duct; and, inside the phallus muscular sheath, the vas deferens forms a narrow ring (but see a similar narrow ring of T. taunaisii in Jurberg et al. 1988, fig. 16) (Barros et al. 1991). Both species were recorded from the city of Rio de Janeiro (Jurberg et al. 1988; Barros et al. 1991; Rangel et al. 2021), and future studies should confirm whether they are indeed distinct, ideally by comparing DNA sequences. Because T. taunaisii was described earlier and has the city of Rio de Janeiro as type locality, whereas T. magnificus was originally cited from Peru but further stated as having Brazil as type locality (Breure 1978), we prefer to adopt the former name.
Two large individuals of T. cf. taunaisii (up to 80 × 32 mm) were temporarily kept in the laboratory (Figure 8 (D–F)), and the eggs plus one juvenile derived from their mating (Figure 8 (G) were released back into the conservation unit. The specimens coupled but did not spawn when reared in the terrarium with many leaves and a little soil; when much more soil was added to the terrarium, the single remaining specimen buried and spawned 30 eggs (maximum length: 10.4 mm), similarly to a conspecific specimen observed in situ, buried and with a smaller spawning (Figure 8 (B,C)). Jurberg et al. (1988) also observed some eggs laid in buried nests. Other ex situ observations largely agreed with those detailed in Jurberg et al. (1988), including activity mainly during the night or on very humid, mild or cold days with addition of water and food. The two specimens voraciously fed on lettuce, and fed as well on kale, yam, carrot, pumpkin, and string bean and much less on fruit (persimmon) peel, but they did not feed on dead leaves (leaf litter).
Geographic distribution
Brazil: Minas Gerais, Rio de Janeiro, São Paulo and Santa Catarina states (Simone 2006), including the city of Rio de Janeiro (Jurberg et al. 1988; Rangel et al. 2021), and possibly also Piauí and Espírito Santo states (Jurberg et al. 1988). Jurberg et al. (1988) argued for a more restricted geographic range, only from the city of Rio de Janeiro, claiming a need for more anatomical data from other sites in order to confirm a wider range.
description: Published as part of Fernandes, Maurício Romulo, Alexandre, Guilherme de Lima & Salgueiro, Fabiano, 2025, Shells, teeth and DNA: land snails from an urban forest in Rio de Janeiro, SE Brazil, pp. 129-169 in Journal of Natural History 59 (1 - 4) on pages 153-155, DOI: 10.1080/00222933.2024.2446580, http://zenodo.org/record/15354306