Stephanodiscus neoaegypticus var. fekrii Flower. Data 2013, var. nov.
Creators: name: Flower, R. J.
name: Keatings, K.
name: Hamdan, M. A.
name: Hassan, F. A.
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Chromista
Bacillariophyta
Coscinodiscophyceae
Thalassiosirales
Stephanodiscaceae
Stephanodiscus
Stephanodiscus neoaegypticus
Stephanodiscus neoaegypticus var. fekrii flower

description: Stephanodiscus neoaegypticus var. fekrii Flower var. nov.
Cell diameters ca. 20–40 µm. Fascicles radial, uniseriate striae occupy ca. 50% of the valve radius. Interfascicles often divide beyond the valve face-mantle junction and slightly widen in the mid-valve region. Central area fultoportulae 2–3. Rimoportulae sub-marginal, 2–3.
Type:— EGYPT. Gharak: Faiyum Depression, 29.14840° N, 30.60976° E, Holocene lake sediment core (GARK1) material, sediment depth 450 cm, collected April–May 2008, (circled specimen (Figs 8, 9) on slide BM 101660, holotype, designated here).
Sediment cores QARU 9 and QARU 10: In the thinly laminated sections of both QARU 9 & 10 (see Fig. 2), a third common Stephanodiscus species was present that was not S. neoeagyptiacus but much more similar to S. galileensis Håkansson & Ehrlich (1987: 20). The type locality for this species is sub-surface (fossil) sediment in Lake Kinneret (Israel). They reported a heterovalvic condition where the concave and convex valves differed with regard to fascicle arrangement and to location of fultoportulae. Since some of their material was evidently rather poorly preserved (see their Figs 3, 14 and 16), the species is re-examined here.
In LM, Stephanodiscus galileensis valves show strong concentric undulations according to the plane of focus either on the marginal or central areas (Figs 19 & 20). Valves range from 20–48 µm in diameter. The marginal area (Fig. 19) also displays a characteristic sub-marginal hyaline silica ring and broad interfascicles. Fascicles are c. 5 in 10 µm, proximally uniseriate with large blocky areolae becoming finer and bi- or triseriate in the distal third portion of the valve. Interfascicles are distinct and about 1.5 µm broad in the midradius area. Concave valves show a similarly strong undulation (Figs 21 & 22) with 5–6 hyaline areas (marking fultoportulae, see below) in the mid-radius position on the valve face (Fig 21, arrowed) and these are particularly obvious in well silicified specimens (Fig. 23). Fascicles on these valves (morphotype ‘B’ of Håkansson & Ehrlich 1987) appear to contain finer areolae and are biseriate for about half the valve distal radius. In this region, interfascicles are often about 1 µm broad but in strongly silicified specimens the width is similar to those in valves with hyaline sub-marginal rings.
In SEM, the external view of convex valves of S. galileensis clearly shows the marked central undulation with irregularly spaced spines subtended from the sub-marginal silica ring (Fig. 24, note the similarity of this specimen with S. aegyptiacus as depicted in Fig. 63, Håkansson & Locker 1981). The fascicles are uniseriate becoming biseriate or triseriate near the valve face-mantle junction (VFMJ) with small areolae (12–13 in 10 µm). External areolar openings are generally <1 µm in the mid valve face area and, consequently, the fascicles are narrower than the interfascicles. Internally, these convex valves (Fig. 25) show marginal fultoportulae on each interfascicle at the VFMJ, one or two sub-marginal rimoportulae (arrowed) and a ring of central area fultoportulae (Fig. 26) with either two or three satellite pores. The mantle areolae, cribra and fultoportulae are generally as in Håkansson & Ehrlich (1987) except in this material the number of central area processes is lower. The concave valves confirm heterovalvy (Fig. 27) with raised interfascicles each subtended by a spine, distinct external openings of central area fultoportulae (arrowed) and a greater degree of areolation (with distally extended bi- and triseriate fascicles) compared to convex valves. Internally, the concave valves display a ring of sub-marginal fultoportulae (Fig. 28, arrowed) that initiate distally an usually biseriate fascicle (Fig. 29). There are typically three oblique sub-marginal rimoportulae (Figs 28–29). Central area fultoportulae possess two (Fig. 29) or three (Fig. 30) satellite pores and occur in depressions near finely porate domed cribra (Fig. 30).
Size distributions:—To help substantiate the two varieties of S. neoeagypticus, diameters of 70 random valves (S. neoaegypticus sensu lato) were assigned to size classes and the distribution plotted (Fig. 31a). These data show a bimodal size distribution with two modal size classes, 30–40 µm and 50–60 µm; the larger class was always composed of S. neoaegypticus valves and the smaller class was mainly S. aegypticus var. fekrii. For S. galileensis, diameters of 60 random valves were assigned to size classes and the distribution plotted (Fig. 31b). There were approximately equal numbers of convex and concave valves resulting in a unimodal size class distribution with 35% of valves in the 30–35 µm size class.
Morphological comparisons:—The morphological characteristics of S. neoaegypticus and S. neoeagypticus var. fekrii are summarized in Table 1 where valve size, extent of uniseriate areolae serve best to discriminate the latter in routine LM examination. Another small form, similar to S. neoagypticus var. fekrii but with distally wider (4/5 areolae) fascicles, was recognised in GARK 1 and tentatively named as cf. asteriodes but this taxon requires further study. Comparable data for S. aegyptiacus from Håkansson & Locker 1981 are included in Table 1 to demonstrate differences between this species and the two newly described S. neoaegypticus taxa. The most discriminating features of the latter are a larger valve diameter range and differences in valve face areolar structure. Strongly concentric valve undulations a distinct marginal hyaline ring and marginal spines are all lacking in S. neoaegypticus sensu lato. The morphological characteristics of S. galileensis obtained from the Qarun core material compare favourably with the published data for this species (Håkansson & Ehrlich 1987) shown in Table 2. The original description and the existence of heterovalvy is generally substantiated and only very minor differences were found in this study. The latter extends slightly the original description by increasing the valve size range and including more variation in the number of rimoportulae and in the arrangement of satellite pores around fultoportulae.
description: Published as part of Flower, R. J., Keatings, K., Hamdan, M. A. & Hassan, F. A., 2013, Stephanodiscus Ehr. species from Holocene sediments in the Faiyum Depression (Middle Egypt), pp. 66-80 in Phytotaxa 127 (1) on pages 73-75, DOI: 10.11646/phytotaxa.127.1.10, http://zenodo.org/record/5085493