Janischewskina Mikhailov, 1939

Liu, Chao, Vachard, Daniel, Cózar, Pedro & Coronado, Ismael, 2023, New species and evolution of the foraminiferal family Janischewskinidae in the middle-upper Mississippian of South China, Palaeontologia Electronica (a 2) 26 (1), pp. 1-27 : 8-10

Genus Janischewskina Mikhailov, 1939

Type species. Janischewskina typica Mikhailov, 1939 .

Diagnosis. Janischewskinidae with interseptal space in some cases with sutural apertures, and development of pre- and post-septal lamellae in the most advanced species.

Description. Test free, nautiloid to compressed laterally, with a juvenarium endothyroid only in the first whorl, passing to planispiral. Coiling follows a progressive increase of the spire. Secondary deposits absent. The most common septa are simple, curved backward. Presence of pre- and post-septal lamellae in the most advanced species, and sutural apertures in the interseptal space. Cribrate aperture in the final whorl, rarely present in the penultimate chambers. Wall microgranular ( Figure 5D ).

Composition. Janischewskina adtarusia Gibshman, Zaytseva, and Stepanova in Gibshman et al., 2020;? J. banphitensis ( Saurin, 1960) ; J. calceus ( Ganelina, 1956) ; J. compressa Sosnina in Sosnina and Nikitina, 1976 (=? J. delicata ); J. delicata ( Malakhova, 1956) ; J. gibshmanae Cózar et al. 2016 ; J. isotovae Lebedeva in Grozdilova et al., 1975; J. lusca ( Saurin, 1960) , J. minuscularia ( Ganelina, 1956) ; J. perretae (Vachard and Cózar in Vachard et al., 2016); J. rovnensis ( Ganelina, 1956) ; J. typica Mikhailov, 1939 (= Samarina operculata Rauser-Chernousova and Reitlinger in Rauser-Chernousova et al., 1940; = J. inflata Wang, 1982 ).

Remarks. Composition of the genus differs notably from that listed in Pille et al. (2010) and Gibshman et al. (2020). Some of the characters used by Gibshman et al. (2020) as distinctive for the genus Janischewskina , such as test shape, coiling symmetry, number of whorls, and wall thickness, are variable characters at species level, but in general, similar in all the genera included in the family Janischewskinidae . Only the interseptal spaces and the lamellae (in the most evolved species) are typical features of the genus, which are not observed in Samarina orbiculata Ganelina, 1956 , nor in Janischewskina ladeinaensis Stephanova and Gibshman, 2017 (= Janischewskina compressa Grozdilova and Lebedeva in Grozdilova et al., 1978), and thus, they are considered herein as Cribrospira . It is noted that some specimens identified as Janischewskina orbiculata ( Gibshman et al., 2020, pl. 1, fig. 7) are reinterpreted as oblique sections of J. typica .

Janischewskina compressa seems to be a junior synonym of J. delicata , although the type material shows very poor orientation as to confirm this synonymy ( Gibshman et al., 2020). Janischewskina inflata shows a wide nautiloid test, with umbilical areas depressed, and secondary apertures in the interseptal space, and herein, it is considered as a junior synonym of J. typica . This overall shape was also observed in Janischewskina sp. in Groves et al. (2012), which is considered also to be this species.

The identification of J. minuscularia in older strata, for instance in the Aleksinian of the Moscow Basin, is a more robust identification than that in younger strata, because for those older rocks, there is no large Janischewskina , of which, its juveniles could be confused. However, in younger levels, the ontogenic evolution of the Janischewskina species has been never studied, and the juveniles of some species seem to be rather similar with those of J. minuscularia . Therefore, the identifications of this species in intervals co-existing with other large Janischewskina are questionable.

Occurrence. Late Viséan-Serpukhovian, northern Palaeotethyan ( Vachard and Le Coze, 2022). The disappearance of the genus commonly occurred in the late Serpukhovian (e.g., Pazukhin et al., 2002; Mazuno and Ueno, 1997), which could allow the recognition of the biostratigraphy for the upper part of the Shuidong section, below the Severokeltmian top ( Figure 2 ). However, the genus has been recorded in strata assigned to the Krasnopolyanian in the Saharan Platform, southern Morocco ( Cózar et al., 2014a), and the Cantabrian Mountain, North Spain ( Cózar et al., 2018), although the conditions in the former region are unusual, and a longer existence of some genera of benthic organisms was recognized ( Cózar et al., 2014b).

Distribution in the Bama Platform. The first occurrence datum of the genus is equivalent to the Mikhailovian Substage, nearly from the base of the Kacai section ( Figure 3 ). However, from the base, large species are recorded (as oblique sections), as well as J. rovnensis ( Figure 5C ) and J. aff. typica , whereas J. minuscularia ( Figure 5A‒B ) take place in intermediate positions within the Mikhailovian. The occurrence of large species of Janischewskina from the base of this interval suggests that it cannot discard the occurrence of J. minuscularia from older levels, as occurs in the Russian Platform. Only in the upper part of the Viséan, J. typica and J. isotovae are first recorded ( Figure 5D‒E ). The abundance of Janischewskina increases notably from the base of the Serpukhovian, and in addition to J. delicata , J. calceus and J. gibshmanae also first occur ( Figure 5F‒H ). Other species previously recorded in the Kacai section ( Figure 3 ) commonly appear from the base of the Serpukhovian in the Shuidong section ( Figure 2 ), where a late occurrence of some species is observed, i.e., J. gibshmanae only occurs from the early-late Serpukhovian transition, together with Bradyina cribrostomata Rauser-Chernousova and Reitlinger in Rauser-Chernousova and Fursenko, 1937 and Eostaffellina ex gr. paraprotvae ( Rauser-Chernousova, 1948d). In the Shuidong section, J. adtarusia ( Figure 5I ) is first recorded from the Zapaltyubian, although the species is rare.

Figures

FIGURE 2 (previous page). Distribution of the Janischewskinidae in the Shuidong section. Red arrows correspond to the productive samples in Janischewskinidae, and black arrows to unproductive samples. Abbreviations: M — mudstone, W — wackestone, P — packstone, G — grainstone; m. — middle, low. — lower, Vis. — Viséan, Bashk. — Bashkirian, Stesh. — Steshevian, Protv. — Protvian, Sever. — Severokeltmian, J. — Janischewskina, B. cri. — Bradyina cribrostomata Zone, Edz — Eostaffellina decurta Zone, Ea-Ep — Eostaffellina actuosa-Eostaffellina prot- vaensis Zone, P. ag — Pseudostaffella antiqua grandis Subzone.

FIGURE 3. Distribution of the Janischewskinidae in the Kacai section. Legend and abbreviations as in Figure 2, and additionally, Alek. — Aleksinian, Tar. — Tarusian, Pr. — Protvian, up. — upper, Jdz — Janischewskina delicata Zone, Bc — Bradyina cribrostomata Zone.

FIGURE 5. Typical representatives of the genus Janischewskina recorded in South China. A‒B. Janischewskina minuscularia? (Ganelina, 1956), HPU-SDB160-278, DPM-PC-SDB143-181. C. Janischewskina rovnensis (Ganelina, 1956), HPU-KC45-7. D. Janischewskina typica Mikhailov, 1939, HPU-KC107-3. E. Janischewskina isotovae Lebedeva in Grozdilova et al., 1975, HPU-KCT4-5. F. Janischewskina calceus (Ganelina, 1956), HPU-SDB160-277. G. Janischewskina delicata (Malakhova, 1956), HPU-KC75-378. H. Janischewskina gibshmanae Cózar et al. 2016, HPU-KC104-3. I. Janischewskina adtarusia Gibshman, Zaytseva and Stepanova in Gibshman et al., 2020, HPU-SDB283-1. (Scale bar equals 1 mm). [HPU- corresponds to the Henan polytechnic University collections in the School of Resources and Environment, KC or SDB to the Kacai or Shuidong sections, respectively, followed by the number of the thin-section, and the final number corresponds to the number of specimens].