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Ostreopsis ovata Fukuyo, 1981

Species Overview:

Ostreopsis ovata is an armoured, marine, benthic dinoflagellate species. It was discovered from French Polynesia, New Caledonia and the Ryukyu Islands, 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 O. ovata are tear-shaped, ovate and ventrally slender (Figs. 1,2). It is the smallest species in the genus. Thecal surface is smooth and ornamented with minute, evenly distributed pores (0.07 µm diameter) (Fig. 3). The suture line between plates at high magnification appears wrinkled and irregular (Fig. 3). Cells have a dorsoventral diameter of 47-55 µm and transdiameter of 27-35 µm (Faust et al., 1996).

Thecal Plate Description:

Thecal plates of Ostreopsis ovata are very thin and delicate, and their morphology is very difficult to preserve. The plate formula for this species is: Po, 3', 7'', 6c, 6s?, Vp, Rp, 5''', 1p, 2''''. In the epitheca, the 1' plate is hexagonal and occupies the left center of the cell (Fig. 1). The apical pore plate (Po) features a short asymmetrical slit-like apical pore, and is associated with narrow apical plate 2' (Figs. 1,4). In the hypotheca, the posterior intercalary plate (1p) is long and narrow (9 x 27µm) (Fig. 2). Plates 3''' and 4''' are large and make up approximately the dorsal half of the hypotheca (Fig. 2) (Faust et al., 1996).

The cingulum is equatorial, relatively wide, and bordered by narrow lists (Figs. 1,2). Within the cingulum, the Vo is situated on the Vp surrounded by the Rp (Figs. 5,6) (Faust et al., 1996). The sulcus contains eight plates (Steidinger and Tangen, 1996).

Morphology and Structure:

Cells of Ostreopsis ovata are photosynthetic containing many golden chloroplasts. Large ovate nucleus is posterior (Fig. 9). Some cells have one or two large red bodies located posteriorly (Fukuyo, 1981).

Reproduction:

O. ovata reproduces asexually by binary fission.

Species Comparisons:

O. ovata differs from the other species in the genus by its small size, very delicate thecal plates and a short, straight apical pore plate (Po). It is readily identifiable from O. siamensis and O. lenticularis by its ovoidal, tear-shaped body (Fukuyo, 1981).

Ecology:

O. ovata can be tycoplanktonic, benthic or epiphytic (Steidinger and Tangen, 1996). 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 species produces an unnamed toxin (Nakajima et al., 1981).

Habitat and Locality:

Ostreopsis ovata is infrequently observed in the field. Populations are usually found in protected, inshore regions from the tropical Pacific Ocean (Fukuyo, 1981, Yasumoto et al., 1987, Quod, 1994), the Caribbean Sea (Besada et al., 1982, Carlson and Tindall, 1985) and the Tyrrhenian Sea (Tognetto et al., 1995). Substrate specificity for this species needs to be determined.

Ostreopsis ovata