Haslea crucigeroides var. australis Cefarelli, Simonato & Mascioni, 2018

Cefarelli, Adrián O., Mascioni, Martina, Simonato, Julián, Almandoz, Gastón O. & Vernet, Maria, 2018, Haslea crucigeroides var. australis, var. nov. (Bacillariophyta), a new marine diatom from southern South America and Antarctica, Phytotaxa 357 (3), pp. 179-188 : 181-183

Haslea crucigeroides var. australis Cefarelli, Simonato & Mascioni , var. nov. ( Figs 2–18 , 22–32 )

LM observations ( Figs 2–18 ): The cells are solitary and have two apically elongated chloroplasts, one on each side of the girdle, visible in valve view ( Fig. 2 ). The frustules are rectangular with rounded corners in girdle view, height ca. 26 μm ( Figs 3, 4 ). The valves are lanceolate to linear with a narrow pseudostauros and acute apices. Length 68.0–172.0 μm, width 8.2–23.5 μm (n = 83) and a highly variable length-to-width ratio (between 4.5 and 10.3) ( Figs 5–18 ). The valve face is domed without a clear distinction from the mantle ( Fig. 4 ). The raphe sternum is central, narrow and straight over the full length of the valve, with a small central area. Transverse striae 20–23 in 10 μm, longitudinal striae 19–24 in 10 μm (n = 29), both of them discernible with LM under an oil immersion objective.

SEM observations ( Figs 22–32 ): Externally, the tegumental layer presents continuous longitudinal fissures demarcating longitudinal strips, except on the valve margin ( Figs 22, 23 ). The central raphe fissures are shaped as enlarged droplets and are deflected towards the same side ( Fig. 23 ). The terminal raphe fissures are strongly deflected to the same side of the valve ( Figs 24, 25 ). The cingulum consists of a valvocopula (ca. 6 μm wide) and a narrower copula, both unperforated ( Fig. 22 ).

Internally, the basal layer is composed of transverse and longitudinal bars, crossed at a right angle delimiting the areolar foramina, the transverse and the longitudinal striae ( Figs 26, 27 , 29 ). The foramina, occluded internally by hymenes ( Fig. 28 ), are generally square, except at the valve margin where they become rectangular in transapical direction ( Fig. 27 ). The pseudostauros, with a thickening of about one central transverse bar, is attached to a short ridge on one side of the central nodule and to a longer ridge on the other side; the latter overlaps the raphe in almost its entire length except for the straight helictoglossae ( Figs 29, 30 ). The two layers of the valve are joined by perforated saepes ( Figs 31, 32 ), except at the valve margin where they are fused ( Figs 27 , 31 ).

Distribution: Haslea crucigeroides var. australis was found during the entire study period in the three sampling sites of the Beagle Channel, at a water temperature of 4.2–9.0°C. It reached a maximum concentration of 720 cells L- 1 at station BF in August 2016 (austral winter, Fig. 1 , Table 1). It was also found with low frequency from net samples near icebergs in Antarctic waters (stations 37 and 100a, Scotia Sea, Table 1) during winter 2008 at water temperatures between -0.68 and -0.26°C and salinities from 34.09 to 34.14.

Holotype: ARGENTINA. Tierra del Fuego Province, Beagle Channel, Almirante Brown Bay (54°51’32.6’’S – 67°30’26.4’’W), plankton sample. Specimen in slide LPC 15222 , illustrated in Fig. 5 , located using England Finder between coordinates G31(2) and G32(1) (Herbarium of the División Ficología, Facultad de Ciencias Naturales y Museo, La Plata, Argentina).

Etymology: the varietal epithet “australis” (austral, southern) refers to the finding of this taxon in the Southern Hemisphere.

Figures

FIGURE 1. Maps showing the study area and the three sampling stations (BD, BE, BF) in Almirante Brown Bay, Beagle Channel, Tierra del Fuego, Argentina.

FIGURES 2–4. LM images of Haslea crucigeroides var. australis, var. nov. 2, 3. Whole cells in valve and girdle view showing the two chloroplasts. 4. Clean frustule in girdle view showing the dome-shaped valves and copulae. Scale bars = 20 μm.

FIGURES 5–18. LM images of different valves of Haslea crucigeroides var. australis, var. nov. ordered from lowest to highest length of their apical axis, exemplifying different shapes and sizes. 5. Holotype. Black scale bar = 20 μm. FIGURES 19–21. LM images of the holotype specimen of Haslea crucigeroides (Hustedt) Simonsen. White scale bar = 10 μm (Figs 19, 21). Black scale bar = 20 μm (Fig. 20)

FIGURES 22–28. SEM images of Haslea crucigeroides var. australis, var. nov. 22. Part of a frustule in girdle view. Note the external tegumental layer with continuous longitudinal fissures, except on the valve margin (white arrows).The cingulum presents the valvocopula and a copula (black arrows). 23. Valve in external view showing continuous longitudinal fissures, raphe sternum and small central area with the raphe fissures. 24, 25.Apices of the same valve showing the terminal raphe fissures strongly deflected to the same side. 26. Entire valve in internal view. 27. Details of the transverse and longitudinal striae in internal view. Note the rectangular areolar foramina at the valve margin. 28. Detail of the foramina occluded internally by hymenes. Scale bar = 10 μm (Figs 22, 26), 2 μm (Figs 23–25, 27, 28).

FIGURES 29–32. SEM images of Haslea crucigeroides var. australis, var. nov. 29. Internal view of a valve centre showing the pseudostauros, the short ridge on a side of the central nodule and the long ridge on the other side. 30. Detail of valve apex in internal view. Note the long ridge covering the raphe until reaching the helictoglossa. 31. Broken valve revealing its two-layer sandwich-type structure; note also its domed shape. 32. Detail of the tegumental and basal layers of the valve (upper and lower side, respectively) joined to each other by saepes (arrow). Basal layer seen on the left of the picture (arrow). Scale bar = 2 μm (Figs 29–31), 0.5 μm (Fig. 32).