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Ostreopsis lenticularis Fukuyo, 1981

Species Overview:

Ostreopsis lenticularis is an armoured, marine, benthic dinoflagellate species. It was discovered as an epiphyte on macroalgae in the Gambier and Society Islands of French Polynesia, and New Caledonia, Pacific Ocean.

Taxonomic Description:

Species in this genus are anterio-posteriorly compressed and are observed in apical or antapical view. The epitheca and hypotheca are not noticeably different in size. Unique features of this genus are on the cingulum. In ventral view the cingulum reveals two prominent structures: a ventral plate (Vp) with a ventral pore (Vo), and an adjacent curved ridged plate (Rp). The distinguishing feature at the species level is the shape of the first apical plate (1') on the epitheca (Fig. 1) (Faust et al., 1996).

Cells of Ostreopsis lenticularis are lenticulate to broadly oval (Figs. 1-3). The cell surface is smooth and covered with randomly spaced pores (0.4 µm diameter) with smooth raised edges (Figs. 1,2,4); the pores are large and round (Fig. 4). Cells have a dorso-ventral diameter of 65-75 µm and a transdiameter of 57-63 µm (Faust et al., 1996, Fukuyo, 1981).

Thecal Plate Description:

The plate formula of Ostreopsis lenticularis is: Po, 3', 7'', 6c, 6s?, Vp, Rp, 5''', 1p, 2''''. The epitheca contains 11 plates. The narrow apical pore plate (Po) is 16 µm long (average) with a slit-like apical pore, and is situated adjacent to apical plate 2' (Fig. 1). The 1' plate is large, irregularly pentagonal-shaped, and situated in the center (Fig. 1) (Faust et al., 1996). The hypotheca is composed of eight plates. Posterior intercalary plate (1p), situated centrally, is a narrow, asymmetric, pentagonal plate (Fig. 2). Plate 1'''' contacts the sulcal region (Fig. 6) (Faust et al., 1996).

The lipped cingulum is narrow and shallow with a smooth edge (Figs. 3,5). It houses a helical, transverse flagellum (Fig. 5). Present within the cingulum is the Vo located on the Vp, and adjacent to the Rp (Figs. 6,7). The shape of the Vp varies from oblong to circular. The sulcus is small and hidden (Figs. 3,7) and contains the longitudinal flagellum (Fig. 7) (Faust et al., 1996).

Morphology and Structure:

Ostreopsis lenticularis is a photosynthetic species with many golden-brown chloroplasts. A large nucleus, and often times a large red body, are located posteriorly (Fukuyo, 1981).

Reproduction:

Ostreopsis lenticularis reproduces asexually by binary fission.

Species Comparisons:

Ostreopsis lenticularis differs from other species in the genus by its lentil-like cell shape, medium size and randomly spaced round pores. The size and location of plates 2''', 3''' and 4''' are also distinguishing features (Faust et al., 1996). This species closely resembles Gambierdiscus toxicus in size, shape and color. However, O. lenticularis has a slightly pointed ventral area, while G. toxicus has a round and indented one (Fukuyo, 1981). O. lenticularis is also similar to O. siamensis in shape and thecal plate configuration (Fukuyo, 1981).

Ecology:

O. lenticularis can be benthic, epiphytic or tycoplanktonic (Steidinger and Tangen, 1996) commonly associated with macroalgae, in the plankton, attached to soft coral and between sand grains. Engulfed cells were often observed in this species collected from Belizean waters indicating mixotrophic feeding. The ventral pore (Vo) is the proposed feeding apparatus (Faust et al., 1996).

Toxicity:

This is a known toxic species; it produces ostreotoxin (OTX), a water-soluble toxin (Tindall et al., 1990), and an unnamed toxin (Ballantine et al., 1988).

Habitat and Locality:

Populations of O. lenticularis were originally found in the Gambier and Society Islands and New Caledonia, Pacific Ocean, associated with macroalgae (Fukuyo, 1981). Populations can be found from tropical shallow waters to offshore reefs (Steidinger and Tangen, 1996). Cells have been observed epiphytic on macroalgae (Dictyota sp. and Acanthophora spicifera) in the Caribbean region (Carlson and Tindall, 1985, Ballantine et al., 1988, Morton and Faust, 1997) and the SW Indian Ocean (Quod, 1994). In the Caribbean, this species has been observed in the plankton (Faust, 1995), attached to soft corals (Ballantine et al., 1985, Carlson and Tindall, 1985) and between sand grains (Ballantine et al., 1985, Carlson and Tindall, 1985, Faust, 1995).

Ostreopsis lenticularis