Ostreopsis ovata
Fukuyo, 1981
Plate 34, Figs. 1-7

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 rigid 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, 6). It is the smallest species in the genus. Thecal surface is smooth, ornamented with minute, evenly distributed pores (0.07 µm diameter) (Figs. 1-4). Cells have a dorsoventral diameter of 47-55 µm and transdiameter of 27-35 µm (Faust et al. 1996).

Nomenclatural Types:
Holotype: Ostreopsis ovata Fukuyo, 1981: figs. 35-38
Type Locality: Pacific Ocean: French Polynesia, New Caledonia and the Ryukyu Islands

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 long and 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 27 µm) (Fig. 2) (Faust et al. 1996).
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 (Fig. 5) (Faust et al. 1996). The sulcus contains eight plates (Steidinger & Tangen 1996).

Morphology and Structure: Cells of Ostreopsis ovata are photosynthetic containing many golden chloroplasts. Large ovate nucleus is posterior (Fig. 6) (Fukuyo 1981). There is evidence of mixotrophy in this species: prey organisms are engulfed via the Vo, the proposed feeding apparatus (Faust et al. 1996).

Reproduction: O. ovata reproduces asexually by binary fission.

Ecology: O. ovata can be tycoplanktonic, benthic or epiphytic (Steidinger & Tangen 1996). Engulfed cells were often observed in this species collected from Belizean waters (Faust et al. 1996).

Toxicity: This species produces an unnamed toxin (Nakajima et al. 1981).

Species Comparisons: O. ovata differs from the other species in the genus by its small size, very delicate thecal plates and a short, straight Po. It is readily identifiable from O. siamensis and O. lenticularis by its ovoidal, tear-shaped body (Fukuyo 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 & Tindall 1985) and the Tyrrhenian Sea (Tognetto et al. 1995). Substrate specificity for this species needs to be determined.

Figure 1: Morphology of a Dinoflagellate

Glossary

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