Cyclotella cassandrae Paillès & Sylvestre, 2018

Paillès, Christine, Sylvestre, Florence, Escobar, Jaime, Tonetto, Alain, Rustig, Sybille & Mazur, Jean-Charles, 2018, Cyclotella petenensis and Cyclotella cassandrae, two new fossil diatoms from Pleistocene sediments of Lake Petén-Itzá, Guatemala, Central America, Phytotaxa 351 (4), pp. 247-263 : 253-256

Cyclotella cassandrae Paillès & Sylvestre sp. nov. ( Figs 23–27 )

Type: Lake Petén-Itzá, Department of Petén, Guatemala, Latitude 16° 15’ 50 N, Longitude 89° 15’ 00 W. Lacustrine sediment in Core PI –6, sample GLAD 9- PET 06-6A-13H2-98.3- 99.3 cm (39.35 m below lake floor), core collected in February 2006.

Holotype: slide PC0612194 deposited at the Laboratoire de Cryptogamie , Museum National Histoire Naturelle ( MNHN) Paris, France.

Isotype: slide Zu/1095 and sediment R 1278 deposited at the Friedrich Hustedt Diatom Study centre in Bremenhaven, Germany..

FIGURES 28–33. Type material of fossil lacustrine diatom Cyclotella cassandrae from lake Peten Itza, SEM. (28) External valve view with cingulum elements, finely punctated short striae and a large elliptical central area slightly transversally undulated. (29) Valve view where the marginal striation is eroded and the central area occupied by a scattered ring of CFP. (30) Lateral view of a valve with two girdle bands, the concentrically undulated marginal area and a steep mantle. (31) Detailed view of the valve margin with at least two pleural bands, on the valve face striae formed by four to six rows of very fine areolae alternating with narrow interstriae, on the mantle on each costae the rounded opening of MFP, an oblong opening (white double arrowhead) representing the external expression of the rimoportula and below the ring of MFP-RM, striae and interstriae are equally finely punctated. (32) Internal view of a broken valve showing short and dense alveoli along the major axis, long and outspread alveoli along the minor axis, a protruding rimoportula generally located along the major axis, ring-scattered CFP on both convex and concave parts of the central area. (33) Internal view showing inserted ribs/striae along the minor axis and MFP on nearly each costae. Scale = 5μm (28–30, 32–33), 2μm (31). Abbreviations: central fultoportulae ( CFP), marginal fultoportulae ( MFP), rimoportula ( RM).

Description

Elliptically shaped valves, diameter 24–46 μm along major axis and 18–30 μm along minor axis. Central area elliptical, slightly transversally undulated with scattered punctae (10 to 25) corresponding to the external opening of central fultoportulae. Central fultoportulae formed by a tube surrounded by two to three satellite pores. Marginal area about one third of valve surface circumferentially undulated with coarse to very coarse striae. Striae of unequal length and density: along major axis 8–12 st/10μm, along minor axis 6–9 st/10μm longer, more outspread and sometimes dichotomous. Striae formed by four to six rows of small rounded areolae (30 in 10 μm). Mantle fultoportulae present on nearly each costa and composed of one tube and three satellite pores. Rimoportula inserted on a costa within the ring of mantle fultoportulae. External openings of mantle fultoportulae and rimoportula in a ring at some distance from the valve margin.

Figures

FIGURES 23–27. Type material of fossil lacustrine diatom Cyclotella cassandrae from lake Peten Itza, LM. (23–24) Valve view at two different focus showing the elliptic shape of the valve, the slightly tangentially undulated central area with scattered puncta, short striae along the major axis, longer and apart striae along the minor axis and at some distance of the valve margin the external opening of MFP (black arrowheads). (25). Valve view with dichotomous striae along the minor axis. (26–27). Size variation of C. cassandrae: large specimen with dichotomous striae and a central area occupied by a scattered ring of puncta, some specimen are more rounded but still elliptic. Scale = 10μm.Abbreviation: central fultoportulae (CFP), marginal fultoportulae (MFP), rimoportula (RM).