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Figure 1. Living chain of Leptocylindrus danicus cells in girdle view. Arrowheads indicate characteristic appearance of valves of adjacent cells. Phase contrast.

Figure 2. Chain of L. danicus in girdle view. Note appearance of valves of adjacent cells. Image modified from Hendey 1964.

Figure 3. Valve view of L. danicus. Note annulus, radial poroid areolae, ring of triangular short spines at valve face/mantle junction, and solitary pore external to annulus. TEM photo.

Figure 4. Valve view of L. danicus. Note radial areolae and irregular ring of triangular short spines at valve face/mantle junction. Valve lacks solitary large pore. Arrowhead indicates hole in underlying Formvar membrane. TEM photo.

Figure 5. Adjacent valves of L. danicus. Left valve is slightly convex, right valve is slightly concave. Annulus is visible in left valve; solitary pore and ring of short triangular spines are visible in both valves. SEM image.

Figure 6. L. danicus spores. Left spore in side view, and right spore in top view. Phase contrast.

Figure 7. Spore of L. danicus. Arrowheads indicate restriction of spines by auxospore envelope during formation. SEM image

Figures (8) Terminal auxospore cell prior to spore formation. (9) Subterminal auxospore formation prior to spore formation. (10) Free-floating spore within auxospore envelope. All images captured via phase contrast.

Species Name: Leptocylindrus danicus
Common Name: None
Synonymy: There are no synonyms for L. danicus, though its identity is often confused with L. minimus. The validity of L. danicus variety adriaticus (Schröder) Schiller and L. danicus variety curvatulus Skvortzov as separate taxonomic entities is questionable. The taxon L. maximus Smayda was invalidly published

    Kingdom Phylum/Division Class: Order: Family: Genus:
    Protista Bacillariophyta Coscinodiscophyceae - - Leptocylindrus

    Use your mouse to rollover the terms in purple for their definitions. If this feature is not supported by your browser, please refer to the accompanying glossary for terminology.

    Species Description

    The weakly silicified cells of L. danicus are cylindrical and occur in chains of up to 20 or more cells. Cell length (pervalvar axis) is normally 3-5 times the cell width (diameter), but occasionally up to 10 times the cell diameter (Figure 2). Adjacent cells are closely abutted. The valve of one cell is slightly convex, while the adjacent valve is slightly concave (Figures 2 & 5), giving a characteristic appearance in the light microscope (Figures 1 & 2). Individual valves are circular, ornamented with uniseriate rows of poroid areolae radiating from the valve center, with a ring of short triangular spines at the junction of the valve face and mantle (Figures 3-5). The poroid rows continue on the mantle to the edge of the valve. There is a narrow annulus (sometimes visible in the light microscope) around the valve center (Figures 3 & 5). Most valves also have a single pore near the center but outside the annulus, some cells have two pores, and rarely there is no pore at all (Figure 4). Based on culture studies, French & Hargraves (1985) suggested that the presence of this pore is correlated with the ability to form resting spores. There are many girdle bands that are approximately trapezoidal in shape and perforated by tiny areolae (Figures 4 & 5). Many of these morphological features are visible only with electron microscopy. Each cell has many small rounded or elongate chloroplasts (Figure 1).

    Resting spores, occurring rarely (see below), are morphologically dissimilar from vegetative cells. Spores are formed within an auxospore envelope

    (Figures 6 & 10), and are composed of two dissimilar valves (Figure 6). The larger valve is adorned with numerous elongate spines (Figures 6 & 7). Resting spore formation may be initiated by nutrient depletion, especially of nitrogen (French & Hargraves 1986).


    Habitat & Regional Occurence

    Leptocylindrus danicus is a coastal and estuarine species. It has a worldwide distribution except for the Arctic and Southern Oceans, occasionally in bloom proportions.

    IRL Distribution

    This species is present throughout most of the year in the central IRL (Hargraves & Hanisak 2011), and infrequent in the northern IRL (Badylak & Phlips 2004). In general, L. danicus is more abundant near the inlets where exchange with coastal water is more extensive, suggesting that populations are frequently renewed by tidal action.



    According to literature records, cell diameters are 5-16 µm


    In diatoms, auxospore formation is a form of sexual reproduction (Round et al. 1990), and infrequent in occurrence. It is also the primary means of restoration of maximum size after diminution through vegetative growth. The co-occurrence of resting spore formation, as part of the sexual process in Leptocylindrus danicus (Figures 8-10), is almost unique among diatoms (French & Hargraves 1985). Spores are rarely seen within the IRL, but occasionally found in adjacent coastal waters (Hargraves, pers. obs.)


    The effect of parasites on the wax and wane of L. danicus populations is unknown, but this diatom can be infected by the nanoflagellates Pirsonia formosa and Cryothecomonas longipes (Kühn et al. 1996; Schnepf & Kühn 2000).


    No information is available at this time


    No information is available at this time


    No information is available at this time


    Badylak, S & EJ Phlips. 2004. Spatial and temporal patterns of phytoplankton composition in a subtropical lagoon, the Indian River Lagoon, Florida, USA. J. Plankton Res. 26: 1229-1247.

    French, FW III & PE Hargraves. 1985. Spore formation in the life cycles of the diatoms Chaetoceros diadema and Leptocylindrus danicus. J. Phycol. 21: 477-483.

    French, FW III & PE Hargraves. 1986. Population dynamics of the spore-forming diatom Leptocylindrus danicus in Narragansett Bay, Rhode Island. J. Phycol. 22: 411-420.

    Hargraves, PE & MD Hanisak. 2011. The significance of chlorophyll size fractionation in the Indian River Lagoon, Florida. Fla. Sci. 74: 151-167.

    Kühn, SF, Drebes, G & E Schnepf. 1996. Five new species of the nanoflagellate Pirsonia in the German Bight, North Sea, feeding on planktonic diatoms. Helgoländer Meeresuntersuchungen 50: 205-222.

    Hendey, NI. 1964. An Introductory Account of the Smaller Algae of British Coastal Waters. Part V. Bacillariophyceae. Ministry of Agriculture, Fisheries and Food. Fisheries Investigations, Series IV. London, IMSO. 317 pp.

    Round, FE, Crawford, RM & DG Mann. 1990. The Diatoms - Biology and morphology of the genera. Cambridge University Press, Cambridge. 760 pp

    Schnepf, E & SF Kühn. 2000. Food uptake and fine structure of Cryothecomonas longipes sp. nov., a marine nanoflagellate incertae sedis feeding phagotrophically on large diatoms. Helgoland Mar. Res. 54: 18-32.

Unless otherwise noted, all images and text by PE Hargraves
Editing and page maintenance by LH Sweat
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Page last updated: 25 September 2011

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