Ardissonea formosa (Hantzsch) De Toni, 1892

Fig. 1

References.

Peragallo and Peragallo 1897-1908, p. 310, pl. 78, fig. 6; Hustedt 1931-1959, p. 233, fig. 720; Sullivan and Wear 1995, p. 181, figs 1-8; Navarro 1982, p. 260, figs 61-63; Navarro and Lobban 2009, p. 136; Lobban et al. 2012, p. 259, pl. 15, figs 4, 5, pl. 16, figs 1, 2; Park et al. 2018, p. 105, fig. 5.

Description from literature.

Hustedt (1931-1959) described this species as linear with ends somewhat narrowed, 200-700 µm long, 15-25 µm wide, 9-10 transapical costae in 10 µm, two rows of areolae between each costa; two or three longitudinal costae and an inner layer, dividing the wall into a series of chambers, each with a single foramen in the inner wall, resulting in three or four chambers. The series of foramina have been described as rows of “pearls,” parallel to the longitudinal lines of the annulus with its underlying costae and sometimes a central costa. Hustedt (1931-1959) specifically referred to a (3rd) longitudinal costa down the middle sometimes, and his fig. 720b shows two rows of foramina between the annular lines, suggesting a costa between them, as the chambers were supposed to have only a single opening. A similar situation is seen in Sullivan and Wear (1995: fig. 4). Hustedt (1931-1959) showed two rows of areolae between the transapical costae, but Sullivan and Wear (1995) reported only one and noted the discrepancy. With SEM they showed that the valvocopula had a prominent notch in the advalvar side and a fimbriate edge to the pars interior. They noted that the areolae at the poles were smaller, circular, less dense and more loosely organized but not an apical pore field.

Materials examined.

Guam: GU44BH-5!, GU26A!, GU52R-2!. Federated States of Micronesia: Yap: Y39A!, Y42-1!. Marshall Islands: Jaluit Atoll: J5!; Bakir Atoll: BA2!.

Observations.

Valves linear with broadly rounded poles, 201-300 µm long, 22-24 µm wide, striae 8-10 in 10 µm, isopolar in both valve and girdle view (Fig. 1A). Plastids numerous, lenticular, displaying peristrophy and karyostrophy depending on light intensity (Suppl. material 3: Fig. S1). Three or five longitudinal lines seen in two focal planes (Fig. 1B, C): if five, the annulus, subtending a longitudinal costa, on the valve face (not hidden at the valve margin), a central line where the offset striae meet; between these, on the inner wall, two rows of foramina (Fig. 1B-D). If three lines, one central row of foramina with no longitudinal costa (Fig. 1F). Two additional rows of foramina along the angle of the valve-mantle junction seen in SEM but obscured in LM (Fig. 1D, F). The pattern of costae underlying the inner wall can be traced in Fig. 1D and seen directly in Fig. 1E. We have also seen specimens with one row of foramina along the midline (Fig. 1F). Commonly one or two longitudinal depressions in valve surface, giving a shallow v (Fig. 1I) or w profile. Striae comprising single row of oval areolae between each transapical costa (Fig. 1C, E, G); loose rows of smaller, circular areolae at the poles, especially noticeable on mantle (Fig. 1I). Narrow pseudoseptum around poles (Fig. 1D, E), elsewhere the double wall forms a thick rim (Fig. 1G). Three girdle bands as follows (Fig. 1F-J). Valvocopula with line of small pores along edge of pars interior, usually obscured in girdle view, deflecting asymmetrically inwards at pole (Fig. 1F), corresponding to location of the notch on advalvar side, which however, is nearly central (Fig. 1I). Interior edge of valvocopula with short fimbriae (Fig. 1G, J). Copula with long fringe of fimbriae at pole, overlapping the valvocopula (Fig. 1H), as described by Sullivan and Wear (1995); an irregular line of pores along abvalvar margin of copula in some specimens (Fig. 1J, arrowhead). Narrow pleura (Fig. 1I, J) with a row of small pores on pars interior.

Taxonomic comments.

The biseriate striae described by Hustedt (1931-1959) and the uniseriate striae in Sullivan and Wear’s (1995) materials suggest that they were observing different species. Sullivan and Wear (1995) observed only two bands on the epicingulum and none on the hypocingulum but we observed the pleura. Ardissonea s.s. superficially resembles Synedra in the current restricted sense (= Catacombas) in shape and double wall but differs in lacking rimoportulae and polar pore fields.