Mathildidae Dall, 1889

Gründel, Joachim & Nützel, Alexander, 2013, Evolution and classification of Mesozoic mathildoid gastropods, Acta Palaeontologica Polonica 58 (4), pp. 803-826 : 804-805

Family Mathildidae Dall, 1889

Remarks.—The family Mathildidae is based on the modern genus Mathilda that has a Pliocene type species. Numerous Triassic to Recent species and several genera are assigned to this family. However, there is no report from the Palaeozoic. Mathildidae are most diverse in the Jurassic and are represented by a large number of species. The principal morphology of the group is rather conservative but various character combinations occur. Few characters seem to be suitable to recognize genera so that the systematics of the Mathildidae is difficult. The number of spiral ribs on the whorl face of the early teleoconch, immediately after the protoconch (primary spiral ribs) seems to be a useful character for a classification on the genus−level. In Mathildidae , there are 2, 3, 4 and sometimes more primary spiral ribs. The spiral rib directly at the suture is here not regarded as a primary spiral rib.

Gründel (1973) used the number of primary spiral ribs for a subdivision in genera and subgenera: Jurilda (later Promathildia ) with two primary spiral ribs, Tricarilda with three primary spiral ribs und Turritelloidea (later Turrithilda respectively Mathilda ) with four and more primary spiral ribs. Other authors considered this subdivision as artificial (e.g., Bieler 1995; Kaim 2004). Kaim (2004) treated Tricarilda − and Turrithilda −species (3 and more primary spiral ribs) under the genus name Mathilda . However, those with two primary spiral ribs were assigned to Promathildia although this character was generally not considered valid by him. Bieler (1995) investigated Recent mathildids and concluded that it is unclear whether the character complex of spiral rib pattern is suitable to recognize monophyletic genera and that anatomical studies (and one may now also say molecular studies) are needed to test whether this pattern give a phylogenetic signal. These doubts may be justified but the need for a subdivision of the large number of fossil mathildids remains. For Jurassic mathildids the number of primary spiral ribs seems a readily available character which in combination with other characters facilitates a subdivision in genera. However, we are aware that this procedure is artificial to some degree. This problem is typical for highly diverse fossil groups which have notoriously conservative shell morphology.

Additional characters which may be used for a taxonomic subdivision are shell shape (e.g., unusually broad and strongly keeled shells) and the presence of a micro−ornament consisting of numerous fine spiral ribs. This micro−ornament seems not to be strictly diagnostic on the genus level; it is for instance weakly developed in some species of Jurilda and Tricarilda but is characteristic for the genera Carinathilda , Angulathilda , and Erratothilda .

As outlined below, the diagnosis of Promathildia is changed because of the new designation of a type species. For those Jurassic mathildids with two primary spiral ribs ( Promathildia sensu Gründel 1997 and Kaim 2004), the name Jurilda Gründel, 1973 is available. Tricarilda Gründel, 1973 can be used for species with three primary spiral ribs. Mathilda Semper, 1865 (with modern type species) is used for species with four and more primary spiral ribs.