Antithala, Harzhauser & Landau, 2021

Harzhauser, Mathias & Landau, Bernard, 2021, An overlooked diversity-the Costellariidae (Gastropoda: Neogastropoda) of the Miocene Paratethys Sea, Zootaxa 4982 (1), pp. 1-70 : 8

Genus Antithala nov. gen.

Type species. Mitra sturi Hoernes & Auinger, 1880 , middle Miocene , Paratethys Sea, Romania .

Diagnosis. Small, broad to moderately broad fusiform to nassariform shells, with beaded sculpture differing from Thala and Mitromica in the development of a parietal denticle and less cyrtoconoid spire, and from Thala in the absence of internal denticles as signs of episodic growth.

Description. Shell small, broad to moderately broad fusiform, with conical to slightly cyrtoconoid, weakly gradate spire with incised suture. Protoconch multispiral, high conical with about three convex to weakly convex whorls. Sculpture of axially and spirally arranged subquadrate nodes, resulting in beaded appearance. Aperture narrow with incised anal sinus bordered by distinct parietal denticle. Outer lip with strong denticles, columella with four folds of which adapical one is most prominent. Siphonal canal moderately long, slightly bent.

Etymology. Combination of anti (ancient Greek: against) and Thala . Referring to Thala H. Adams & A. Adams, 1853 into which the Paratethyan Antithala species have been placed so far.

Included species. Antithala claviformis nov. sp., Antithala filipescui nov. sp., Mitra neugeboreni Hoernes & Auinger, 1880 , Mitra sturi Hoernes & Auinger, 1880 .

Stratigraphic and geographic range. Only known so far from middle Miocene (Badenian) deposits of the Central Paratethys Sea, recorded from Romania, Hungary, Bosnia and Herzegovina, and Poland.

Palaeoenvironment. The localities represent middle neritic palaeoenvironments with soft bottoms. No occurrences from coastal-neritic settings are known.

Discussion. Rosenberg & Salisbury (2003) separated the genus Mitromica Berry, 1958 from Thala H. & Adams, 1853 based, most importantly, on the evidence of episodic growth in Thala , attested by the presence of former outer lips retained as internal denticles ‘varices’ in members of that genus, whereas Mitromica shows continuous growth. Other shell features cannot separate the two genera. According to Rosenberg & Salisbury (2003), Mitromica ranges from the Caribbean, Bahamas, Florida and Bermuda, the Eastern Pacific, southern Madagascar, South Africa, and West Africa, whereas Thala is restricted to the Indo-Pacific, with an overlapping range in South Africa.

Antithala shares features in common with Vexillum Röding, 1798 , Mitromica and Thala . The prominently beaded sculpture and shell shape are reminiscent of some Mitromica and Thala species , but those genera lack a parietal denticle, their suture is distinctly less incised, and the base is less constricted. Vexillum develops a similar aperture with a parietal denticle bordering the anal canal, but differs in its sculpture, which is dominated by axial elements, lacking prominent spirally arranged subquadrate beads. Bellardithala nov. gen. differs in its episodic growth and the absence of a parietal denticle.

Key to Paratethyan Antithala nov. gen. species

1. Spire whorls with three rows of nodules................................................................... 2

- Spire whorls with four rows of nodules.................................................................... 3

2. Columella with three folds......................................................................... A. sturi

- Columella with four folds.............................................................. A. claviformis nov. sp.

3. Columella with three folds................................................................... A. neugeboreni

- Columella with four folds, adapical much stronger............................................ A. filipescu nov. sp.