Species Description: This genus consists of very elongate and narrow needle-like cells that are differentiated from the closely related Thalassionema by the absence of small spines along the valve margin. The three known species were formerly in the genus Thalassiothrix (Hasle & Syvertsen 1997). In L. elongatum, the two ends of the cell are different. The “head” pole is somewhat club-shaped with a single apical spine (Fig. 1A, modified from Hasle & Syvertsen 1997; and Fig. 2, SEM); the “foot” pole is gradually narrowed, and lacks a spine (Fig. 1B, modified from Hasle & Syvertsen 1997; and Fig. 4, live cell, phase contrast). Rudimentary secondary spines have been reported on the “head” pole (Rivera and Cruces 2007). A wide hyaline area (sternum) extends the length of the valve, and a row of complex areolae extends along each valve margin (Fig. 3, SEM), becoming reduced near the apices. Scattered along the length of the cell are many small chloroplasts (Fig. 4, valve view of foot pole, live cell, phase contrast; Fig. 5, girdle view of head pole, live cell, phase contrast)
The reported size from literature sources is 738-2040µm long, 3-4µm wide, with 8-14 areolae in 10µm. It was found rarely in the IRL, mostly about 1200µm long, and 3.6-3.8µm wide, with 10-11 areolae in 10µm (Fig. 3). It has a wide tropical distribution, mostly reported from the Pacific Ocean, but has probably been overlooked or misidentified in some areas, since it resembles the more common L. pacificum that is also occasionally present in the IRL. Further details of the morphology and distribution are found in Hasle (2001). It was found only near the Fort Pierce Inlet in summer of 2008 and 2013, and is probably adventitious.
Hasle GR, Syvertsen EE. 1997. Marine Diatoms. pp. 5-385. In: Tomas C (Ed.), Identifying Marine Diatoms and Dinoflagellates. Academic Press (NY).
Hasle GR. 2001. The marine, planktonic diatom family Thalassionemataceae: morphology, taxonomy and distribution. Diat Res 16: 1-82.
Rivera P, Cruces FR. 2007. On the diatom Lioloma elongatum (Grunow) Hasle (Thalassionemataceae) off the Chilean coast. Diat Res 22: 491-493.