DICYCLINIDAE Loeblich & Tappan 1964

Family DICYCLINIDAE Loeblich & Tappan 1964 View in CoL (diagnosis sensu Loeblich & Tappan, 1987) Genus Dicyclina Munier-Chalmas 1887 (see Table 1 for diagnosis)

Dicyclina is morphologically one of a group of agglutinating genera characterised by a large, flattened disc with an initial embryonic stage (forming the thickest part of the test), followed by a small planispiral stage (or no planispiral stage at all) and finally a post-embryonic stage where the characteristic biseriate chambers are added annularly or cyclically (i.e., Cyclolina , Cyclopsinella , Mangashtia and Dicyclina ). These are also somewhat reminiscent of porcellaneous forms such as Broeckina . Dicyclina differs from all the others in that it has a relatively large and complex embryonic apparatus, and that it adds successive annular chambers alternately either side of the median equatorial plane (i.e. in two alternating layers analogous to the term “biserial”). The other annular genera herein add successive single annular chambers across the median plane. Some genera (e.g., Mangashtia , Cyclopsinella ) may give the appearance of 2-layers of chambers as their annular chambers have a series of radial pillars or clusters of pillars in the middle of the chambers but these “chambers” therefore do not alternate.

As with all LBF, a descriptive terminology when naming the fossilised parts of the organism’s shell is required and variations of these are often used to discriminate between taxa. The nomenclature and characteristics of internal structures are especially important. A comprehensive illustrated glossary of descriptive terms applied to the study of foraminifera in general was provided by Hottinger (2006) which has achieved “standard” status among most workers and is followed here. Members of the Dicyclinidae (which at present includes only the genus Dicyclina ) display variably complex internal structures and Figure 20 View Fig shows, in very generalised schematic form, the broad disposition and identity of these.

Specific variation in Dicyclina is based primarily on (a) the nature of the embryonic apparatus ( Figure 20 View Fig part a); (b) the number and disposition of both the radial (“beams”) and transverse (“rafters”) elements which together evolve externally to form a subepidermal network beneath the outer test wall ( Hottinger, 1978) and (c) the general shape (in axial cross-section) of the primary chamber septa and attachments thereto such as other “rafters” and the annular “groove” or “gutter” running close to the free edge of the septa ( Figure 20 View Fig part b).

In some cases when dealing with these morphological attributes, the exact nature of these features; their relationship to other features; and their biological function(s) are not clear or are unknown. Theoretically, elongated unclosed (stolons) or tubular closed (canals) spaces serve for protoplasmic flow or differentiation of protoplasmic activity in foraminifera (see e.g. Hottinger & Dreher, 1974). For example, in species of Dicyclina (studies of which are challenged in general by a lack of suitable material) both the form and function of the annular “groove” or “gutter” are imperfectly known with some workers (e.g., Schlumberger & Choffat, 1904, and Neumann, 1967) showing the “gutter” as fully enclosed, whereas we believe (see inset image in Figure 20 View Fig ) the “gutter” is open and connected to the foramina and is an active part of the protoplasmic flow system.

Another feature imperfectly known is the nature and position of the radial (i.e., running from the embryonic region in the direction of annular growth) “grooves” or “canals” which lie in between the radial partitions themselves (“beams”) and which – although shown herein running immediately below the outer chamber wall (which is removed in our schematic illustration) – could equally be positioned at the lower part of the transverse “rafters”.

Meanwhile for the purposes of this article the “naming of parts” is sufficient to provide a useful descriptive framework.

The (generally) large diameter and relative thinness of the Dicyclina test, plus the tendency for its post-embryonic disc to undulate, means that specimens in thin section are seldom complete and oriented optimally to display many of the features mentioned above. Moreover, because of the disc-like nature of the test with the embryonic zone at the centre, it is very often difficult to discern on which side of the embryo the sub- and supra-embryonic zones are in fact placed (this is not an issue in conical genera like Orbitolina ). This makes identification to species level especially challenging in random sections and even important taxonomic elements are sometimes not observed in type material (see Dicyclina qatarensis and Table 5 below). In practice, many specimens cannot be identified more definitively than “ Dicyclina sp. ”, even when a species name has been attached. Saint-Marc (1974, 1981) did not identify Dicyclina beyond generic level in his material from Lebanon, presumably in acknowledgement of this issue.

Furthermore, some transverse sections of species of Dicyclina – especially when only fragmentary – resemble fragmentary axial sections of non-discoidal/cyclic genera such as Cuneolina (e.g., compare Figure 17 View Fig of C. ex gr. pavonia with Figure 22 View Fig of D. schlumbergeri herein). Cherchi & Schroeder (1990a) (following Brönnimann et al., 1983 and others) hypothesised that Dicyclina had in fact developed from Cuneolina by becoming fully annular and based on (p. 330) “… identical internal chamber structures and a very pronounced initial spiral stage, which was more and more reduced in the course of the phylogenesis ”. To this one might add that Dicyclina has a larger, more complex embryonic apparatus than even the most advanced Cuneolina . In practice, some specimens are best identified as “ Cuneolina / Dicyclina sp. ” ( Simmons et al., 2020; see also discussion in section on Cuneolina ex gr. pavonia in this paper).

The status of Dicyclina taxonomy remains somewhat ambiguous. Schroeder & Neumann (1985) in their extensive treatment of mid-Cretaceous larger foraminifera did not include Dicyclina (or Cuneolina for that matter) in their work, stating that they are “… still subject of anatomical and taxonomical problems to be solved. ” (p. 8). Despite subsequent smaller publications on Dicyclina by Cherchi & Schroeder (1990a, b), and as is clear from the following discussions on the genus and the individual species, these problems have yet to be fully resolved.

The online WoRMS catalogue of foraminifera records six possible species of Dicyclina ( Hayward et al., 2025) . Of these, Dicyclina lusitanica Egger, 1902 belongs in the genus Anchispirocyclina ( fide Hottinger, 1967 ) and Dicyclina aegyptiaca Hewaidy, 1993 lacks sufficient internal description to distinguish it as a Dicyclina and to separate it from possible synonyms (thus a taxon inquirendum pending further study of type material). In any case, it (and the associated “ Dicyclina sp. A ”) were described from Maastrichtian strata and are thus outside

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the focus of this paper. Therefore, four species of Dicyclina are included herein: Dicyclina schlumbergeri Munier-Chalmas 1887 (the type species of the genus); D. qatarensis Henson 1948b ; D. simplex Cherchi & Schroeder 1990a and D. sampoi Cherchi & Schroeder 1990b . They are distinguished from one another by a combination of overall size (diameter), embryonic apparatus size and complexity (i.e., the presence/absence of secondary chamberlets in the supra- or sub-embryonic zones), and whether transverse subepidermal partitions (in this case, “rafters”) are limited to the inside of the peripheral chamber wall or also occur on the septa (as shown in Figure 20b View Fig ). The numbers of (a) annular chambers per mm radius and (b) radial partitions (“beams”) per quadrant are also used. Overall chamber shape in axial section may also be useful, at least for distinguishing D. simplex from other taxa ( Figure 21 View Fig ). D. qatarensis is probably the most poorly described/defined and Cherchi & Schroeder (1990b) regarded it as (p. 210) “… a badly defined and unrecognisable species ” citing a lack of a megalospheric embryo visible in the type material. It is also excluded from general discussions of Middle East Dicyclina by Schlagintweit & Rashidi (2018) and Schlagintweit & Yazdi-Moghadam (2021). The species as can currently be best understood is further discussed below.

On the other hand, D. schlumbergeri is a very widelyreported taxon over a long stratigraphic interval (late Albian-Maastrichtian – but see discussion below) and it is likely that this has been used as a “bucket” term for dicyclinids found in random orientations that are technically indeterminate at species level if using “best practice”. This emphasises the need for deliberate or fortuitously good, oriented sections, ideally displaying the embryonic apparatus, septa, and sub-epidermal partitions which show both genus and species characteristics before arriving at a specific determination ( Frijia et al., 2015).

Prior to 1990 and the introduction of D. simplex and D. sampoi (Cherchi & Schroeder, 1990a, b), almost all records of Dicyclina , if assigned to a species, were assigned to D. schlumbergeri . Cherchi & Schroeder (1990a, b) challenged this paradigm implying that there was an evolutionary plexus from D. simplex (e.g. Cenomanian) to D. schlumbergeri (e.g. Coniacian and younger) with D. sampoi (e.g. Cenomanian) forming a separate Arabian Plate evolutionary lineage. D. simplex has a relatively simple embryonic apparatus and D. schlumbergeri a complex one, thus Cherchi & Schroeder (1990a) envisaged an evolution plexus of embryonic apparatus development similar to that seen in the Orbitolininae (e.g. Schroeder, 1975; Schroeder et al., 2010). That D. sampoi has a complex embryonic apparatus and occurs in the Cenomanian suggests it belongs to a separate lineage according to Cherchi & Schroeder (1990b). Although many authors have ignored or were unaware of this (i.e. continuing to use D. schlumbergeri as a sensu lato term), the large number of records of Dicyclina published since 1990 allow the hypothesis of Cherchi & Schroeder (1990a, b) to be tested.

In summary (see discussion of each of the four species of Dicyclina below), the phylogeny of Dicyclina is a little more complex than envisaged by Cherchi & Schroeder (1990a, b) and some subsequent workers. All validated records of Dicyclina in Coniacian – Maastrichtian strata are D. schlumbergeri with D. simplex restricted to the Cenomanian and D. sampoi to the Cenomanian –?Turonian. However, D. schlumbergeri is also known from the middle – late Cenomanian of Mexico only. Thus, it appears that independent lineages of Dicyclina with a complex embryo appeared in the Cenomanian in both Mexico ( D. schlumbergeri ) and the Arabian Plate ( D. sampoi ). By Coniacian times, D. schlumbergeri had replaced D. sampoi or a repetitive form of evolution had occurred. The relationship to D. simplex is unclear.

The morphological details “above” of the differences between the four species are discussed in the individual species treatments and summarised in Table 5 and (excluding D. qatarensis ) in Figure 21 View Fig .

As a genus, Dicyclina is widely known from Neotethys (as far east as the Arabian Plate) and the Caribbean in rocks ranging in age from supposedly Albian to Maastrichtian (e.g. Cherchi & Schroeder, 1990a, b). Within this review we have been unable to confirm any Albian records of Dicyclina and even early Cenomanian records are doubtful. Such specimens may have been confused with Cuneolina . Omaña et al. (2019) state that D. schlumbergeri is very common in the Albian and Cenomanian strata of Mexico but offer no clear-cut evidence of Albian occurrences. Rey et al. (1977) report but do not illustrate Dicyclina sp. from the late Albian of Portugal. Saint-Marc (1974, 1978) places the inception of Dicyclina in the middle Cenomanian in Lebanon, although in his 1981 work the Neotethyan inception of the genus occurs within the early Cenomanian. Herein we consider Dicyclina to be a middle Cenomanian – Maastrichtian genus, at least in terms of confident records of its occurrence.

Biozonations utilising Dicyclina (e.g. Wynd, 1965; Taslı et al., 2006; Omidvar et al., 2014b; Haftlang et al., 2020; Omidi et al., 2018) are typically recognising a local biofacies, rather than a chronostratigraphically significant discrete range.