Involutina, Terquem, 1862

Rigaud, Sylvain, Blau, Joachim, Martini, Rossana & Rettori, Roberto, 2015, Taxonomy, phylogeny, and functional morphology of the foraminiferal genus Involutina, Acta Palaeontologica Polonica 60 (1), pp. 235-244 : 237

Taxonomy of Involutina

The genus Involutina was introduced by Terquem (1862: 450), prior to the advent of the International Rules for Zoological Nomenclature (IRZN). Terquem (1862) described two species within the genus: Involutina silicea Terquem, 1862 and Involutina jonesi Terquem and Piette in Terquem, 1862 ( Terquem 1862: 450–451 and 461, respectively), but did not mention which one was the type-species for the genus. Some authors have considered I. silicea as the type-species (e.g., Loeblich and Tappan 1954). However, in an earlier work, Bornemann (1874) recognized differences in the wall composition of the two species and, by placing I. silicea into Ammodiscus Reuss, 1862 , he only retained I. jonesi in Involutina . Because, as stated by Brady (1864), I. jonesi is a junior synonym of I. liassica (Jones in Brodie, 1853), Nummulites liassicus Jones in Brodie, 1853 (= now Involutina liassica ) must be regarded as the type-species of Involutina ( Brady 1864; Bornemann 1874; Wicher 1952; Kristan 1957; Koehn-Zaninetti 1969; Gušić 1975; Piller 1978; Loeblich and Tappan 1987).

It is generally believed that the genus Involutina is characterized by a high interspecific variability and numerous species have been introduced into the genus based on differences observed in the test and tubular chamber morphology. Our study, however, emphasizes that these traits display a large range of variability at the specific level, calling into question the validity of these species. Very few forms can be convincingly separated from I. liassica even with a thorough statistical analysis. For example, there is no reliable criterion that permits the distinction between I. farinacciae Brönnimann and Koehn-Zaninetti, 1969 and I. liassica . Likewise, in our material, along the ontogeny, the tubular chamber section of I. liassica appears oval to triangular (e.g., Fig. 2F) and is formed either by a complete or a semi tube (see Piller 1978 for definition) ( Fig. 2A–F). Therefore, the validity of I. turgida Kristan, 1957 based either on the interpretation of Kristan (1957) or Piller (1978) is dubious (see also Gušić 1975).

In the literature, the diversity of Involutina had already been revised downwards. Some species ( I. silicea Terquem, 1862 , I. aspera Terquem, 1864 , I. polymorpha Terquem, 1864 , and I. limitata Terquem, 1864 ) have been excluded from Involutina on account of the agglutinated nature of their wall ( Bornemann 1874) and the Early Cretaceous species Involutina stinemeyeri Church, 1968 as it would not possess the morphological characteristics of the genus ( Brönnimann and Koehn-Zaninetti 1969). Among the remaining species, most have been placed into synonymy with the type-species Involutina liassica (Jones in Brodie, 1853) (see Bornemann 1874; Wicher 1952; Kristan 1957; Koehn-Zaninetti 1969; Gušić 1975; Piller 1978). For example, the species Involutina ticinensis ( Schweighauser, 1951) is regarded as the microspheric form of I. liassica ( Kristan 1957; Koehn-Zaninetti 1969).