Medlinella Frankovich, Ashworth & M.J. Sullivan, 2016

Frankovich, Thomas A., Ashworth, Matt P., Sullivan, Michael J., Veselá, Jana & Stacy, Nicole I., 2016, Medlinella amphoroidea gen. et sp. nov. (Bacillariophyta) from the neck skin of Loggerhead sea turtles (Caretta caretta), Phytotaxa 272 (2), pp. 101-114 : 105

Medlinella Frankovich, Ashworth & M.J. Sullivan , gen. nov.

Frustules are rectangular in girdle view with bluntly rounded ends and porose girdle copulae ( Figs 1–4 , 11 ). Septa are evident on the copulae of whole frustules in girdle view (arrows in Figs 1–4 ). Septa are also evident in valve view when copulae remain attached to valves (arrows in Figs 7, 9 ). Valves are isopolar and semi-lanceolate with a convex dorsal margin and a slightly concave ventral margin inflated in the middle ( Figs 5–10 , 12, 13 ). The valve face is strongly asymmetric around a narrow axial area, superficially resembling the genus Amphora Ehrenberg ex Kützing (1844: 107) with distinct dorsal and ventral striae ( Figs 5–10 , 12–16 ). The striae are composed of circular to transapically elongated areolae that are partially occluded by volae ( Figs 12–18 ). Apical pore fields are absent. The raphe-sternum is eccentric and displaced towards the ventral margin ( Figs 5, 8–10 , 12–16 ). The raphe is generally straight to slightly arched ( Figs 12–16 ). The external proximal raphe ends are spathulate, weakly deflected towards the ventral margin, and terminate where the fascia extends towards the valve margins ( Figs 12, 13, 15 ). The external distal raphe ends are angularly hooked towards the ventral margin with some variation in the angularity of the bends ( Figs 12–16 ). Small slightly thickened hyaline areas on the primary side of the valves are located near the valve apices adjacent to the distal raphe ends ( Figs 12–16, 18 ). Internally, the raphe is located on a slightly raised and thickened sternum ( Figs 19–22, 24 ). The internal proximal raphe ends are straight, simple, closely spaced, and partially obscured by a pair of small knob-like to flap-shaped structures present at the raphe ends ( Figs 19–22 ). The internal distal raphe ends are straight and terminate on weakly developed helictoglossae ( Figs 19–20 ). Pseudosepta are absent. The cingulum ( Figs 11 , 25–26 ) is composed of many bands (up to 12 observed) that are open at one end. The bands of the cingulum ( Figs 11 , 25–30 ) are differentiated into three types: the valvocopulae that have septa ( Figs 24 , 27 ), the second copulae that have septa at the opposite pole ( Figs 26, 28 ), and additional abvalvarly located copulae ( Figs 11 , 25, 26, 29, 30 ) that have shallow, or partially developed septa (arrows in Figs 29, 30 ). The valvocopula is flanged inward on the pars interior where it attaches to the valve ( Figs 25, 27 ). The flange is expanded as a large tab located in the middle on the dorsal side where it aligns with dorsal side of the internal central area of the valve ( Figs 22, 23 , 25, 27 ). The valvocopula septum is located on the pars exterior ( Figs 24 , 27 ).

Type:— Medlinella amphoroidea Frankovich, Ashworth & M.J. Sullivan , sp. nov.

Etymology:— the generic name honors Dr. Linda K. Medlin (Marine Biological Association of the United Kingdom) in recognition of her important research on “marine gomphonemoid diatoms”.

Figures

FIGURES 1–10. Medlinella amphoroidea. Type population, LM. 1–4. Frustules in girdle view showing size range and morphological variation.Arrows in Figs 2, 4, 7, 9 indicate septa. 5–10. Specimens in valve view showing size range. Scale bar = 5 μm.

FIGURES 11–18. Medlinella amphoroidea. Type population, SEM, external views. 11. Entire frustule in girdle view showing cingulum with 8 copulae visible. Single rows of pores are evident on the copulae. Note that the hypovalve with its attached valvocopula (not visible) is partially collapsed on the left side of the image towards the frustule interior. 12. Broken valve showing shape of longer valves. 13. Whole valve showing orientation of striae, eccentric raphe-sternum, and fascia. 14. Dorsal striae and valve apex showing raphe branch, hyaline area (arrow) on primary side of valve adjacent to the angularly hooked distal raphe end. 15. Detail of central area and valve apex on right side of specimen depicted in Figure 13 showing volate pore occlusions, spathulate and slightly deflected proximal raphe ends, and hooked distal raphe end. 16. Detail of valve apex on left side of specimen depicted in Figure 13 showing angularly hooked distal raphe end that points towards the ventral margin. 17. Whole valve in side view showing orientation of ventral striae and the extension of the fascia onto the valve mantle. 18. Whole valve in side view showing orientation of dorsal striae and a single shortened stria on the valve margin adjacent to the central area. “=” indicate the same specimen. Scale bars: Figs 11–13, 17, 18 = 2 μm, Fig. 14 = 0.5 μm, Figs 15, 16 = 1 μm.

FIGURES 19–24. Medlinella amphoroidea. Type population, SEM, internal views. 19. Whole valve. 20. Detail of central area and valve apex showing the raphe located on a slightly raised and thickened sternum. 21. Detail of central area of the valve depicted in Fig. 19. 22. Oblique view of central area of valve with attached valvocopula showing the attachment of the central tab of the valvocopula to the dorsal side of internal central area and a pair of small knob-like to flap-shaped structures present at the internal proximal raphe ends. 23. Oblique view of central area of valve with attached valvocopula (v) and second copula (c2), each with a single row of pores. 24. Valve with attached valvocopula showing detail of pars exterior of valvocopula septum. “=” indicate the same specimen. Scale bars: Fig. 19 = 2 μm, Figs 20–24 = 1 μm.

FIGURES 25–30. Medlinella amphoroidea. Type population, SEM. 25. Valve with attached cingulum showing central tab (arrow) of valvocopula (v) with 11 additional copulae in side view. 26. Valve with attached partial cingulum in oblique view showing the pars interior of the septum of the second copula (c2). 27. Pars interior of valvocopula showing flanged margin, central tab on the pars interior, and septum located on the pars exterior. Arrow indicates open end of valvocopula. 28. Second septate copula with 2 attached additional copulae. Note smaller pores on copula 3 (arrow). 29. Copula of undetermined order showing partially developed septum (arrow). 30. Copula of undetermined order showing shallow septum (arrow). Scale bars: Figs 25–28 = 2 μm, Figs 29, 30 = 1 μm.