Prorocentrum texanum Henrichs, Steidinger, Scott et Campbell sp. nov. Figs. 1, a–f; a–e; and 4, a
Diagnosis: Photosynthetic prorocentroid dinoflagellate. Round to oval cell, length 35.3–46.3 μm (field; n = 56); 24.9–37.6 μm (culture; n = 177), median = 40.7 μm (field), 31.9 μm (culture), widest width: 31.2–40.6 μm (field; n = 56); 20.6–37.2 μm (culture; n = 177), median = 36.7 μm (field), 31.1 μm (culture). Both valves with radiating tangential rows of ejectosome pores have a posterior circle of ejectosome pores and a central circle of pores. On the right valve, there are 5–6 recessed, cylindrical pores below the periflagellar platelets, whereas on the left valve there are no ejectosome pores below the periflagellar area, but beyond the a platelet there are ~7 pores along the margin, occasionally a doublet, and to the other side usually 4–5 pores. The broad, shallow, V-shaped periflagellar area is typically composed of 10 platelets, has a prominent anterior, serrated solid flange supported by the a periflagellar platelet, and an opposing short, flat flange on the h platelet. Large, posterior U-shaped nucleus, two parietal chloroplasts, each with a compound, interlamellar pyrenoid not clearly visible in light microscopy, pusules, fibrous vesicles, and trichocysts.
Holotype: slide of isolate “PrTX B” deposited in Type Collection of Dinoflagellates, National Museum of Natural History, Smithsonian Institution, catalog number 5142.
Isotypes: Fixed material of isolate “PrTX B” deposited in the Texas A & M University S. M. Tracy Herbarium; accession numbers 264776__01, 264776__02, 264776__03 and in the Type Collection of Dinoflagellates, National Museum of Natural History, Smithsonian Institution, catalog numbers 5150, 5151, and 5152 with associated SEM images (Figs. 2a–2c).
Type Locality: Ship Channel, Port Aransas, TX, USA (27°50′17″ N, 97°03′01″ W).
Culture Strain: “PrTX B,” DW Henrichs, 3 Feb 2010, Deposited in the Provasoli-Guillard National Center for Marine Algae and Microbiota (CCMP3349).
Habitat: Marine, planktonic.
Etymology: Species name reflects state of Texas waters where this species was originally observed and isolated.
Additional Description: Both left and right valves with shallow depressions and two-sized pores. The ejectosome pore pattern anteriorly on the right and left valves differs in relation to the periflagellar area and margins (Fig. 2a, b, d and e). There are prominent circles of rimmed, recessed cylindrical ejectosome pores on both left and right valves (Fig. 2b and c). One circle is central, the other is posterior. Each valve has eight to eleven rows of tangential ejectosome pores. The U-shaped nucleus is central to posterior (Fig. 1b), and intertwined between the two yellow-brown chloroplasts. Right valve has the slightly raised periflagellar area of 10 platelets in a broad V-shaped indentation. Periflagellar platelets surround a flagellar pore and an accessory pore (Fig. 3a). Left and right valves are slightly different anteriorly around the periflagellar area, but otherwise they are similar in surface markings. Markings consist of shallow depressions and two different sized valve pores. The larger, rimmed pores are recessed short cylinder-shaped holes with a pore at the bottom; they range from 0.23 μm to 0.33 μm in diameter (n = 10). The smaller pores are fewer and range from 0.08 μm to 0.16 μm in diameter (n = 10). Peripheral pores follow the margin and some are associated with tangential radiating pores on both valves. Radiating pores from the valve margin extend to the central circle of ejectosome pores (Fig. 2d and e). The pore patterns are either circular, semicircular, straight, or follow a peripheral contour (Fig. 2a and e). There are two prominent circular patterns, one posterior made of 8–10 pores and just below a semicircular (8–10 pores) pattern and the other central consisting of usually 8–12 pores with smaller pores inside the circle. The posterior circle is usually incomplete in the anterior direction (Fig. 2c and e). This posterior pattern is common among species in the P. micans clade. The central circle is about twice as large as the posterior circle. The 8–11 tangential, radiating pore rows on each valve consist of up to 6 ejectosome pores. Anteriorly in the periflagellar area there is a prominent serrated flange (2.8–4.6 μm long) with 2–6 teeth-like projections (Figs. 2c and 4e); this flange is on platelet a and can appear as a spine in valve view. Opposite that serrated flange is a short flat flange located on platelet h. On the right valve, there are 5–6 pores under the broad V-shaped periflagellar indentation, whereas on the left valve, beyond periflagellar platelet a, there are 5–7 pores along the periphery, occasionally a doublet (Fig. 2). The periflagellar area is composed of 10 platelets (Fig. 3), similar to, but different from, that of P. micans. Two of the designated plates (e and g) are split into two sections, but retain their relative position and are considered homologous. The flagellar pore (FP) is irregular and larger than the accessory pore (AP) and is formed by platelets c, f, g2, e2, and e1, whereas the AP is formed by b, d, and c and is distinctly round. In P. texanum platelet a supports the 3–5 μm flange whereas platelet h supports the flat short flange.
Figure 1. Prorocentrum texanum var. texanum. Light micrographs of live, cultured cells (a–c): (a) one intact cell in valve view, one in sagittal view, and one right valve with raised periflagellar area; (b) 4′-6-Diamidino-2-phenylindole-stained (blue) posterior nucleus (N) in valve view; (c) two recently divided cells showing parietal yellow-brown chloroplast (Ch) in daughter cells. Transmission electron micrographs of P. texanum var. texanum (d–f): (d) longitudinal thin section showing the periflagellar area with two spine-like projections, wavy chloroplast lamellae with a distinct interlamellar pyrenoid (Py), and a large posterior nucleus (N); (e) section showing periflagellar area with spines below which are fibrous vesicles (Fv), pusule vesicles (Pv), and trichocysts (T); (f) sagittal section of cell with anterior fibrous vesicles, trichocysts (T), and ejectosome pores (arrows), Scale bars = 20 μm (a, b, c), 5 μm (d), 2 μm (e, f).
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Figure 2. (a–c) Scanning electron micrographs of preserved cultured Prorocentrum texanum var. texanum cells. (a) Right valve with broad V-shaped periflagellar area, trichocyst pore pattern adjacent to the periflagellar area (short arrows), and central circular pore pattern (dashed line); (b) left valve with anterior peripheral pore pattern (short arrows), central circular pore pattern, and rows of tangential ejectosome pores (long arrow); (c) scanning electron micrograph of preserved field material showing right valve with a serrated flange, anterior ejectosome pore pattern (short arrows), and the posterior incomplete circle of pores (dashed line). Scale bars = 20 μm (a–c). (d and e) Drawings of the right and left valves of P. texanum var. texanum showing the various pore fields; (f) drawing of the right valve of P. texanum var. cuspidatum showing the various pore fields. All drawings are proportional.
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Figure 3. (a) Proportional drawing of Prorocentrum texanum's periflagellar area with all platelets labeled: a through h. The a platelet supports the serrated flange and the h plate supports the shorter flat top flange; (b) periflagellar platelets of P. micans, after Fensome et al. (1993); (c) periflagellar platelets of P. minimum, after Fensome et al. (1993).
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On the anterior left valve the pattern is different with no pores under the periflagellar area. In sagittal view (Fig. 1a and c), the cell depth is equal on both sides and one valve is not deeper than the other. The megacytic zone can be longitudinally or horizontally striated.
Organelles: A large posterior U-shaped nucleus with continually condensed chromosomes (Fig. 1d) and a nucleolus occupies about one-fourth to one-third of the cell volume and intertwines between the two chloroplasts. One chloroplast occupies each valve (Fig. 1a and c). Each yellow-brown chloroplast has a central compound, interlamellar pyrenoid that can be quite distinct (Figs. 1d and 4f). The pyrenoid has parallel double-thylakoid lamellae (Fig. 1d insert) transecting it which immediately separates it from the remainder of the chloroplast lamellae that are convoluted and unevenly spaced in a stroma matrix (Fig. 1d). Starch granules have been observed in the cytoplasm. At the light microscope level, cells can have 1–2 large anterior pusules that vary in size. At the ultrastructure level, the area of the pusule is occupied by vesicles and some of those vesicles are filled with fibrous material. Fibrous vesicles resembling mucocysts I and II have been found in the cytoplasm, most notably under the periflagellar area (Fig. 1d–f). The species does have typical dinoflagellate trichocysts with a paracrystalline rod that exits through a raised pore (Fig. 1d–f); trichocysts are numerous and found throughout the cell, anteriorly and posteriorly. Other organelles include tubular mitochondria and golgi. The transverse flagellum beats in an elliptical path tangential to the longitudinal flagellum, both arise anteriorly from the flagellar pore.
Figure 4. Prorocentrum texanum var. cuspidatum. Light micrographs of live cultured cells (a–c): (a) heart-shaped and dorsally pointed cell with yellow-brown chloroplasts and prominent rigid flange (“winged spine”), and extruded trichocysts (arrowheads); (b) cleared valves, separated right and left valves reveal characteristic pore patterns; (c) 4′-6-Diamidino-2-phenylindole-stained posterior V-shaped nucleus (blue). (d and e) Scanning electron micrographs of preserved cultured cells showing right valve views with periflagellar area, characteristic tangential rows of ejectosome pores, circular pore fields, and the serrated anterior flange (see Fig. 2f). (f) Longitudinal oblique, thin section showing distinctive wavy chloroplast lamellae (Ch), prominent pyrenoid (Py), partial nucleus (N), pusule vesicles (Pv) anteriorly under the periflagellar area, fibrous vesicles (Fv) anteriorly, and a trichocyst (T). Scale bars = 20 μm (a–e), 5 μm (f).
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There are two varieties that maintain their distinct morphology under the same culture conditions, one is broadly round to oval, P. texanum var. texanum, and the other is broadly oval and posteriorly attenuated to pointed, P. texanum var. cuspidatum var. nov. Both varieties are genetically identical and co-occur, but P. texanum var. texanum has been the dominant form in blooms from the type locality.
Prorocentrum texanum var. cuspidatum Henrichs, Steidinger, Scott et Campbell, var. nov. Figs. 2, f, 3, a–f
Diagnosis: Differs from P. texanum var. texanum only in shape and size, and consequently, shape of the posterior nucleus. The cell is ovoid to heart shaped with one side more curved, posteriorly pointed, and slightly larger than the variety texanum. Length: 33.0–43.9 μm (culture; n = 133), median = 38.8 μm (culture), widest width: 23.5–33.5 μm (culture; n = 133), median = 28.1 μm (culture). In sagittal view, the cell tapers due to dorsal attenuation.
Additional Description: Similar to the variety texanum, but cell shape different based on valve curvature. Cells more like a broad P. micans with serrated thick anterior flange (3.2–4.8 μm long) appearing as a winged tooth in light microscopy. Posteriorly the cell is attenuated and is usually pointed. Opposite from the serrated flange is a prominent short flange. Valve pore patterns and cytology are identical to P. texanum var. texanum except for a large V-shaped dorsal nucleus that can occupy up to one-third the cell volume (Fig. 4c). Nuclear shape may depend on cell shape. In sagittal view the cell is tapered from anterior to posterior. Other cytological features (Fig. 4f) are identical to var. texanum in that there is a prominent central, compound, interlamellar pyrenoid, fibrous vesicles anteriorly under the periflagellar area near the pusule vesicles, trichocysts, and other typical dinoflagellate organelles such as tubular mitochondria and golgi.
Holotype: Slide of isolate “P1015” deposited in the Type Collection of Dinoflagellates, National Museum of Natural History, Smithsonian Institution, catalog number 5143.
Isotypes: Fixed material of isolate “P1015” deposited in the Texas A & M University S. M. Tracy Herbarium; accession numbers 264777–01, 264777–02, 264777–03 and in the Type Collection of Dinoflagellates, National Museum of Natural History, Smithsonian Institution, catalog numbers 5153, 5154, and 5155 with associated SEM images (Figs. 3d–3e).
Type locality: Ship Channel, Port Aransas, TX, USA (27°50′17″ N, 97°03′01″ W).
Culture Strain: “P1015,” DW Henrichs, 16 Oct 2009, Deposited in the Provasoli-Guillard National Center for Marine Algae and Microbiota (CCMP3350).
Habitat: Marine, planktonic.
Etymology: The varietal name reflects the cells attenuated and sometimes pointed posterior end.