Medlinella amphoroidea 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 : 106-107

Medlinella amphoroidea Frankovich, Ashworth & M.J. Sullivan , sp. nov. ( Figs 1–26 )

LM morphology: Valve apices are rounded and slightly bent towards the ventral margin ( Figs 5–10 ). Valve morphometrics are as follows: length 7.0–13.0 μm, n = 19, width 1.5–2.5 μm, n = 17, length-to-width ratio 3.3–6.5, n = 14. The dorsal and ventral stria densities are 22–30, n = 19, and 26–35 in 10 μm, n = 10, respectively (determined from LM and SEM images). The central area is formed by a wide asymmetric rectangular to bow tie-shaped fascia that extends towards the valve margins ( Figs 5–10 ). The septa on the valvocopulae and 2 nd copulae extend over ca. 1/7 of the frustule length from the apices ( Figs 1–4 ). SEM morphology: Externally, the valve face and mantle have uniseriate transapical striae ( Figs 11–18 ). The dorsal striae are nearly parallel in the valve middle becoming radiate towards the apices, 25–34 in 10 μm, n = 17 ( Figs 12–16, 18 ). The dorsal striae continue on to the valve mantle uninterrupted ( Figs 12–16, 18 ) with up to 5 areolae per stria on the valve face and mantle in the middle of the valve adjacent to the fascia ( Fig. 18 ) gradually decreasing to 1 or 2 areolae that wrap around the apices ( Figs 12–16, 18 ). The ventral striae are interrupted at the valve face-mantle transition with a single apical row of smaller circular to oval areolae located on the valve face adjacent to the raphe and a single row of larger transapically elongated areolae located on the valve mantle ( Figs 12, 13, 15–17 ). The ventral striae are strongly radiate in the valve middle becoming parallel and finally convergent at the valve apices, 30–36 in 10 μm, n = 12, ( Figs 13, 15–18 ). Smaller areolae are occluded by a single simple or branched vola ( Figs 13–16 ). Wider, transapically elongated areolae are occluded by multiple volae (up to six observed) arranged in an alternate or irregular pattern ( Figs 13–16 ). The central area is large, forming an asymmetric rectangular to bow tie-shaped fascia that extends to the valve margins and is wider on the ventral side ( Figs 11–13, 15, 17, 18 ). Occasionally, shortened striae are present at the dorsal valve margin adjacent to the central area ( Fig. 18 ). The valvocopula and the second copula have a single row of apically elongated pores around the perimeter, pore densities: 28–30 in 10 μm, n = 5 ( Figs 22–28 ). The remaining copulae have a single row of slightly smaller pores, 32–45 in 10 μm, n = 6 ( Figs 11 , 25, 26, 29, 30 ).

Type:— UNITED STATES. Florida: Florida Bay , samples removed from the skin in the dorsal neck area of loggerhead sea turtles Caretta caretta , 24° 55’ 01” N, 80° 48’ 28” W, B. A. Stacy, 24 June 2015 (holotype CANA! 124075, illustrated as Figs 1–5, 7–30 ; paratypes CAS! 223049, illustrated as Fig. 6 , ANSP! GC59142 , BM! 101808, BRM! ZU10 /31. The holotype slide and paratype slides are specimens from separate individual turtles) .

Etymology:— refers to the resemblance of the valves of Amphora in the valve view.

Taxa relative abundances:— Forty-nine taxa from 24 genera were observed from the neck skin of five loggerhead turtles. The relative abundances of the newly described M. amphoroidea ranged from 13% to 50%. Medlinella amphoroidea was the most abundant taxon in 3 of the samples. Hyalosynedra cf. laevigata ( Grunow 1877: 166) D.M. Williams & F.E. Round (1986: 316) was the second most abundant taxon comprising 2% to 62% of the valve counts. At the third rank, the most abundant taxon was Tursiocola denysii Frankovich & Sullivan ex Frankovich et al. (2015: 228) , comprising 5% to 43% of the valve count. 5% of the valves remained undetermined at the genus and/or at the species rank. Only four other taxa (i. e. Mastogloia cuneata ( Meister 1937: 268) Simonsen (1990: 134) , Navicula sp. , Achnanthes sp. , and Nitzschia sp. exhibited mean relative abundances>1%). The remaining taxa observed were common benthic forms.

Re-examination of the type slides of Tripterion kalamensis and T. philoderma

Valves of both Tripterion kalamensis and T. philoderma are heteropolar and clavate with a broadly rounded head pole and a narrower foot pole ( Figs 31, 32 ). For both species, the raphe is straight and the central area is formed by a wide asymmetric bow tie-shaped fascia that terminates at or near the edge of the valve face ( Figs 31, 32 ).

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.

FIGURES 31–32. Tripterion kalamensis and T. philoderma. Type populations, LM, specimens in valve view showing valve and frustule shape, size range, and separated copulae. 31. Tripterion kalamensis (holotype slide ANSP! GC64443a), arrows indicate septum on copula (top arrow) and open end of copula (bottom arrow). 32. Tripterion philoderma (holotype slide ANSP! GC17182a), arrows indicate lack of septa in separated copulae. Scale bars = 10 μm.