Prorocentrum concavum

P. concavum is a benthic species that can also be tycoplanktonic. Cells can be either motile or embedded in mucus attached to detritus (Faust 1990b; Steidinger & Tangen 1996).

P. concavum populations are often associated with floating mangrove detritus and sediments in tropical and neritic waters (Faust 1990b; Steidinger & Tangen 1996).

P. concavum is a photosynthetic species with golden-brown chloroplasts (Faust 1990b). Two cup-shaped pyrenoids are also present (Fukuyo 1981).

Holotype: Prorocentrum concavum Fukuyo, 1981: figs. 13-19, 49
Type Locality: Pacific Ocean: French Polynesia, New Caledonia and the Ryukyu Islands

P. concavum reproduces asexually by binary fission.

Prorocentrum concavum, at the LM level, is difficult to differentiate from a number of other Prorocentrum species due to their similar size and shape; e.g. P. concavum is often confused with P. lima (Fukuyo 1981; Faust 1990b), but P. lima is not areolate and bears marginal pores (Faust 1990b). The location and arrangement of areolae on the surface of P. concavum closely resembles that of P. hoffmannianum (about 670/valve) (Faust 1990b) and P. belizeanum (about 950/valve) (Faust 1993a); however, the latter two species have fewer areolae per valve and also have marginal pores, while P. concavum does not (Faust 1990b). P. concavum and P. tropicalis (Faust 1997) have similar intercalary bands: granulated and horizontally striated.

Prorocentrum concavum is an armoured, marine, benthic dinoflagellate. This toxic species is often associated with floating detritus and sediments in tropical and neritic waters.

P. concavum is a bivalvate species often observed in valve view. Cells are broadly ovoid. Valve centers are concave and flattened (Figs. 1, 2, 5-7). Cells measure 50-55 µm in length and 38-45 µm in width. The valve surface is covered with 1000-1100 prominent shallow areolae. The areolae are round to oval with smooth edges (Figs. 1, 3) and often observed with a central pore (0.8 µm diameter) (Fig. 3). No marginal pores are present and the cell center is devoid of areolae (Fig. 5). The intercalary band is granulated and horizontally striated (Figs. 1,2) (Fukuyo 1981; Faust 1990b).
The periflagellar area is a narrow, rimmed, V-shaped depression on the right valve (Figs.1, 4, 5, 7). It is composed of eight apical plates, without ornamentation, fitted with a large flagellar pore, and a much smaller auxiliary pore (Fig. 4). The left valve is slightly indented anteriorly with a thickened apical ridge (raised margin) bordering the periflagellar area (Fig. 1) (Fukuyo 1981; Faust 1990b).

This species is known to be toxic, producing the following toxins: fast-acting toxin (FAT) (Tindall et al. 1984), diarrhetic shellfish poison (DSP) toxins (Hu et al. 1993), okadaic acid (OA) (Dickey et al. 1990), and an unnamed toxin (Tindall et al. 1989).