Hyalosynedra laevigata

Sabir, J. S. M., Theriot, E. C., Lobban, C. S., Alhebshi, A. M., Al-Malki, A. L., Hajrah, N. H., Khiyami, M. A., Obaid, A. Y., Jansen, R. K. & Ashworth, M. A., 2018, Systematics of araphid diatoms with asymmetric rimoportulae or densely packed virgae, with particular attention to Hyalosynedra (Ulnariaceae, Bacillariophyta), Phytotaxa 347 (1), pp. 1-49 : 9-12

Hyalosynedra laevigata from Rabbit Key Basin, Florida ( Figs 10–16 )

Description: —Length was 223.0–307.4 μm and width 5.0–8.0 μm ( Figs 10, 12 ). Ends were very weakly subcapitate in some specimens ( Fig 11 ). Ocellulimbi were 18–26 pores wide ( Fig. 13 ). Sterni were thin along the whole length of the valve. The outlines were convex in the center, becoming linearly converging to the ends with either parallel or subcapitate ends. Virga densities were from 51–55 in 10 μm, and pore densities in the ocellulimbus were 6–7 in 1 μm.

As in the type material, the ocellulimbi in external view were weakly sunken ( Fig 13 ) with three rows of pores, and typically fringed at the top by 4–5 spines. The roughly triangular hyaline area above the ocellulimbus was often fringed with large distinct pores. Striae were biseriate ( Figs 13, 14 ). Internally, the rimoportulae were asymmetric, again with the lip towards the apex being the smaller with the larger lip curled slightly around it ( Fig. 15 ). The external rimoportula opening was expressed as a sunken pore near the midline. Internally, the hyaline end region was depressed, with the asymmetric rimoportula just inside the depression on the few specimens observed.

Girdle bands were dissociated from one another and the valves in the cleaned cultured material, but all girdle bands found were without pores ( Fig. 16 ) and all were open as previously described for H. laevigata ( Williams & Round 1986) .

Remarks: —The Rabbit Keys, Florida sample contained specimens most resembling the Grunow material we identified as H. laevigata . Although longer and wider than the type material, our specimens formed a continuum in length and width, and we could find no qualitative or outline character separating it from the Grunow material.

Figures

FIGURES 10–12. Hyalosynedra laevigata from Rabbit Keys Basin, Florida, HK510. 10. Bright field LM of valve outline. 11. Detail of valve apex in LM. Rimoportula visible at arrow. 12. SEM of exterior whole valve.

FIGURES 13–16. Hyalosynedra laevigata from Rabbit Keys Basin, Florida, HK510. 13. Valve apex exterior with external rimoportula opening and weakly sunken ocellulimbus. 14. Valve center with sternum and details of fascicles. 15. Valve apex interior with rimoportula and terminal pore field. 16. Dissociated girdle bands.