Thalassiosira livingstoniorum Prasad, Hargraves et Nienow
The genus Thalassiosira is one of the most species-diverse diatoms in the IRL system, and it is unsurprising that new species are found here. One group of Thalassiosira consists of at least 10 species and varieties with tangentially undulate valves (Fig. 1, SEM). The present species has not been recognized previously as separate from T. cedarkeyensis (Prasad et al. 1993) until recently (Prasad et al. 2011). This species differs from T. cedarkeyensis in its larger size, the higher density of areolae, arrangement and distribution of fultoportulae and rimoportula (Fig.1, arrow), the presence of a subcentral irregular ring of fultoportulae (Fig. 2, SEM), and the lack of occluded processes. In contrast to many Thalassiosira species, colony formation was not observed, though cells were observed with extruded chitin fibers (Fig. 2, arrowheads), the common means of colony formation in this genus
In the IRL, valve diameters were seen at 13-24µm, with 23-25 areolae in 10µm and 5-7 marginal fultoportulae in 10µm. The rimoportulae (Fig. 1, arrow) is approximately equidistant from two fultoportulae in, often raised and interior to, the marginal ring of fultoportulae. The internal labiate portion of the rimoportula is somewhat oblique to the radius (Prasad et al. 2011). Living cells have many discoid chloroplasts. Resting spores were not seen. At present, T. livingstoniorum has been identified primarily from coastal waters of the eastern Gulf of Mexico, and occasionally in the IRL, primarily in the summer.
Prasad AKSK, Nienow JA, Hargraves PE. 2011. Plicate species of the diatom genus Thalassiosira (Bacillariophyta) from the Atlantic and Gulf coasts of southeastern United States, with the description of T. livingstoniorum sp. nov. Proc Acad Nat Sci Philadelphia 161:1-34.