Neocyclotus prominulus (d’Orbigny, 1837)

Neocyclotus prominulus (d’Orbigny, 1837) View in CoL

( Figures 2 (F–H), 12(D–K))

Records in PNM da Cidade sta. 1, 5 April 2022 [3 sh, MNRJ 23828 View Materials ; 1 sh, MNRJ 23838 View Materials ; 1 spm, MNRJ 23829 View Materials ]; sta . 1, 14 May 2022 [1 sh]; sta. 8, 13 August 2022 [1 spm, MNRJ 22884 View Materials ]; sta . 15, 5 November 2022 [1 spm].

Description of jaw (MNRJ 23829)

Jaw V-shaped or triangular (depending on the orientation), with a median line separating the two nearly rectangular plates, each measuring 767 µm long; masticatory border with 11–12 triangular/trapezoidal projections in each plate, increasing in height from 35 µm (first, proximal projection) to 87 µm (ninth or tenth, distal); each projection consisting of one or two (first and last projections) to eight rectangular subunits/scales (ninth or tenth projections), assuming a nearly rectilinear or slightly oblique orientation, apparently having the same width among different projections; scales adjacent to the masticatory border or on the opposite margin with squared shape, 12–17 µm long; scales in the middle portion of the plate with a rectangular shape, 21–25 µm long, 9–12 µm wide (length:width ratio up to 2.6), assuming a slight oblique orientation in relation to the squared scales; most scales completely rugose, with micro-pores disposed in a trabecular matrix, except by the continuous border.

Remarks

Simone (2004) described and illustrated the operculum and radula of this species, but only partly described the morphology of the jaw and did not illustrate it. In relation to this structure, he cited a ‘surface constituted by several oblique striae’, which probably consists in the rectangular scales found in the middle portion of the jaw plate ( Figure 12 (F–I)).

Geographic distribution

Brazil: Minas Gerais, Rio de Janeiro, São Paulo and Paraná states ( Simone 2006), including the city of Rio de Janeiro (eg Rangel et al. 2021).