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 : 238-240

Genus Involutina Terquem, 1862

Fig. 2A–I.

1965 Pachyspirillina Ruggieri and Giunta ; Ruggieri and Giunta 1965: pl. 2: 2, 4, 6; type species Pachyspirillina lacunosa Ruggieri and Giunta, 1965 .

1974 Hensonina Moullade and Peybernès ; Moullade and Peybernès 1974: pl. 3: 6–9; type species misidentified as Trocholina lenticularis Henson, 1947 .

Type species: Nummulites liassicus Jones in Brodie, 1853; Lias at

Fretherne; Gloucestershire, United Kingdom, by subsequent designa-

tion of Brady (1864).

Species included: As previously mentioned, Involutina liassica displays a large range of variability in its test size and shape, tubular chamber morphology and position relative to the previous whorl, lamellae thickness, papillae size, number, and repartition, and perforation size and connection. Herein we consider that I. liassica (Jones in Brodie,

1853) (Rhaetian–early Middle Jurassic) and I. hungarica ( Sidó, 1952)

Aptian–Albian) are the only described species presenting distinct morphological characteristics. In I. liassica , the test is dominantly lenticular, the papillae are uneven, and the wall perforations may merge in the umbilical mass whereas in I. hungarica , the test is mostly subglobular ( Schlagintweit and Piller 1990), the papillae are equidimensional, and the perforations are radially distributed and straight ( Brönnimann and Koehn-Zaninetti 1969). An additional, non-described species, which is very rare in our Early Jurassic material, also shows intrinsic features. Its test is discoidal, its lamellae are thin and only slightly undulated (forming short papillae), and its perforations are rather small in length and diameter ( Fig. 2H, I).

Emended diagnosis. — Test free, discoid, lenticular, to subglobular. Globular proloculus followed by a planispirally enrolled and undivided tubular chamber with successive coils possibly showing irregularities or oscillations. Well-developed, at least in the juvenile part and on both sides of the tubular chamber, the lateral laminar extensions of the tube wall (L2 lamellae sensu Piller 1978) are laterally tapered, interfingering in the umbilical region ( Fig. 2A, B, D, E, H), and locally thickened, forming papillae at the test surface. Wall calcareous, perforate, originally fibrous aragonitic (see Hohenegger and Piller 1975). Aperture simple, terminal.

Remarks. — The type-species of Involutina ( Nummulites liassicus Jones in Brodie, 1853) was first included into the genus Nummulites Lamarck, 1801 . Numerous criteria allow the distinction between Involutina and Nummulites . The most striking dissimilarities are in the wall composition (aragonitic in Involutina , calcitic in Nummulites ), the chamber arrangement (undivided tubular chamber in Involutina , multichambered in Nummulites ), and the higher level of complexity in the canal system of Nummulites .

In the literature, confusion exists between the genera Involutina and Ammodiscus Reuss, 1862 (e.g., in Loeblich and Tappan 1954). Doubts have been cleared up following the works of Kristan (1957) and Hohenegger and Piller (1975). The latter authors have irrefutably demonstrated the aragonitic nature of the Involutina wall. It is now assumed that the aragonitic, involute, laminar, and perforate test of Involutina is clearly different from the agglutinated, evolute, and imperforate test of Ammodiscus .

The genus Radiospirillina Blau and Wernli, 1999 is a perfect homeomorph of Involutina . Their difference is only based on their wall composition and structure. In Radiospirillina , the wall is calcitic with hyaline radial umbilical masses and a monocrystalline tubular chamber whereas in Involutina the wall is entirely fibrous aragonitic.

MHNG- 2011-1-9; J 1, isolated specimen with distinct bumps; J 2, enlarged view of J 1; J 3, sectioned, polished, and etched specimen; J 4, enlarged view of J 3 showing significant laminae discontinuities; J 5, enlarged view of J 4 showing detail of a bump. Note the limited lateral extension of the bump and the good preservation of the aragonite needles. Abbreviations: e-h, rudimentary egg-holder; i, interfingered (lamellae); m.c., merged canals; p, perforation; pap, papilla; p.l., papillose lamella; s.c., straight canal; t.f., tube floor. Scale bars 50 μm.

Among Involutinina , Involutina shows affinities with the genus Planispirillina Bermúdez, 1952 but contrary to Involutina , Planispirillina presents an asymmetric test with a spiral side devoid of papillose lamellae. In isolated specimens, Involutina may be confused with Papillaconus Rigaud, Blau, Martini, and Rettori, 2013a . The mode of coiling, trochospiral in Papillaconus allows their distinction. From Aulotortus Weynschenk, 1956 , Involutina only differs in the presence of papillose lamellae.

In 1965, Ruggieri and Giunta have introduced the Middle Jurassic genus Pachyspirillina that presents the same morphological characteristics as the genus Involutina . While Ruggieri and Giunta (1965) have considered that Pachyspirillina belongs to the monocrystalline Spirillinidae Reuss, 1862 , Loeblich and Tappan (1987) have placed the genus in synonymy with Involutina (aragonitic). Doubt remains about the wall composition of Pachyspirillina and consequently, its validity cannot be confirmed or contested yet. Two species have been included in Pachyspirillina by Ruggieri and Giunta (1965). The type-species Pachyspirillina lacunosa Ruggieri and Giunta, 1965 (pl. 2: 4, 6) is perfectly homeomorphous with Involutina liassica . Its test is planispirally coiled, perforate, and presents, a waved periphery (probable papillae) in section. If proved to be aragonitic, the species should be placed in synonymy with I. liassica . Conversely, the second species, Pachyspirillina (?) involutinoides Ruggieri and Giunta, 1965 (pl. 2: 20–22), questionably assigned to Pachyspirillina , has a low trochospiral coiling. According to Blau and Wernli 1999), the species must be assigned to the genus Radiospirillina Blau and Wernli, 1999 , which displays a monocrystalline wall. However, if aragonitic, the species should be rather included into the genus Piriniella Blau, 1987a (see Rigaud 2012; Rigaud et al. 2013a). It is worth to note that the specimen illustrated by Ruggieri and Giunta (1965) as Pachyspirillina n. gen., sp. ind. (1965: pl. 2: 2) shows a sub-centered, oblique section of the species “ Pachyspirillina ” lacunosa .

In 1974, Moullade and Peybernès have introduced the new genus Hensonina for planispiral Involutinidae presenting a reticulate umbilical ornamentation, a criterion that would allow its distinction from Involutina , which shows umbilical masses covered by “pillars” (i.e., papillae). Although they have mentioned that their material permitted them to observe this reticulate ornamentation, none of the illustrated specimens ( Moullade and Peybernès 1974: pl. 3: 6–9) has evidenced such structure.A reticulate ornamentation is, however, present on the spiral side of the specimens illustrated by Henson (1947) as Trocholina lenticularis Henson, 1947 and Trocholina lenticularis minima Henson, 1947 that Moullade and Peybernès (1974) considered as the generotype of their new genus. The latter species, asymmetric in shape and in its ornamentation, has been recently assigned to the genus Hensonipapillus Schlagintweit, Rigaud, and Wilmsen, 2015 . Hensonipapillus lenticularis is characterized by a trochospiral type of coiling and possesses a complex canal system (see illustrations in Henson 1947; Brönnimann and Koehn-Zaninetti 1969; Arnaud-Vanneau et al. 1988). According to Piller (1978) and Schlagintweit and Piller (1990), the specimens illustrated by Moullade and Peybernès (1974) must be referred to Involutina hungarica ( Sidó, 1952) and the genus Hensonina Moullade and Peybernès, 1974 should be placed into synonymy with Involutina .

Stratigraphic and geographic distribution. — Late Triassic (late Norian?–Rhaetian), Early–Middle Jurassic, and Aptian–Albian of Tethys.