Modulidae P. Fischer 1884

Family Modulidae P. Fischer, 1884

Landau et al. (2014), working on both Recent and fossil taxa, divided the family Modulidae into six genera. This classification is based on the general morphology of the shell. The aperture, and in particular the siphonal area (Fig. 2, arrows) is regarded as the main diagnostic feature.

Laevimodulus Landau et al., 2014 and Psammodulus Collins, 1934 are exclusively fossil tropical American genera, with several records in the Miocene-Pliocene. Trochomodulus Landau et al., 2014 is another tropical American genus represented from the late Early Miocene to the present-day Caribbean and Panamic regions. The genus Modulus Gray, 1842 contains most of the recent and fossil Caribbean-Panamic species and also includes the West-African species. Trochus tectum Gmelin, 1791, the only species of Modulidae in the Indo-Pacific, is also the type species of the genus Indomodulus Landau et al., 2014. Indomodulus tectum is widespread throughout the Indo-Pacific. However, Trondlé (1989) argued that based principally on the shell colour of the aperture at least two species can be distinguished in French Polynesia: Indomodulus tectum and Indomodulus candidus (Petit de la Saussaye, 1853). A molecular analysis is urgently needed to clarify this systematic debate. The genus Conomodulus Landau et al., 2014 is based on two fossil species from the Miocene of Indonesia.

Most of the American species classified in the genera Modulus, Trochomodulus, and Laevimodulus share the same reinforced siphonal depression, which is well-delimited by a siphonal ridge (Fig. 2 B, C). The monotypic Mio-Pliocene American genus Psammodulus has a shallow siphonal depression, but this genus is unusual amongst Modulidae because of the coarse grains of sand adhering to the surface of the shell.

The European fossil genus Incisilabium Cossmann, 1918 (Middle Eocene, Bartonian), the oldest unambiguous member of Modulidae (Cossmann & Pissarro 1907, pl. 3 fig. 22-1), bears a broad siphonal depression that is not reinforced and not delimited by a groove or ridge (Fig. 2 F). The type species is also characterized by its regular rows of nodes and the total lack of an umbilicus. Indomodulus tectum (Gmelin, 1791) (and its varieties) bears a shallow siphonal depression, which is poorly delimited (Fig. 2 A), and has the highest whorl expansion rate resulting in the largest body whorl relative to the spire of the group.

Species of Conomodulus have a high spire and differ from other modulid genera by a wider and deeper siphonal groove (Landau et al. 2014). We have examined the specimens of Conomodulus preangerensis (Martin, 1905) figured by Landau et al. (2014) [RGM.794.179, late Miocene, early Tortonian of Bontang, East Kalimantan, Indonesia (locality TF 505), Height 12.0 mm; RGM.312.287, middle Miocene, lower Menkrawit beds, East Kalimantan, Indonesia (locality 391), Height 5.0 mm (incomplete)] and have observed that these specimens have weak lirae on the inside of the outer lip and a shallow siphonal groove (Fig. 2 E).

Judging from the general shape, particularly by the high spire, the new species from New Caledonia cannot be included in the Indo-Pacific genus Indomodulus and appears related to the Indo-Pacific Neogene genus Conomodulus.