Coolia monotis Meunier, 1919
Species Overview:
Coolia monotis is an armoured, marine, benthic dinoflagellate species. It a toxic species with world-wide distribution.
Taxonomic Description:
Species in this genus are anterio-posteriorly compressed and are observed in apical or antapical view. A distinguishing feature is the shape and size of the apical pore plate (Po) (Faust, 1992).
Cells of Coolia monotis are compressed; round and lens-shaped (Figs. 1-3). The axis is oblique. The rounded epitheca is slightly smaller than the rounded hypotheca (Figs. 3,5). The thecal surface is covered with well defined plates delineated by a network of intercalary bands (Figs. 1-7). Cell size ranges from 25 to 45 µm in diameter and 30 to 50 µm in length (Fukuyo, 1981, Dodge, 1982, Tolomio and Cavolo, 1985b, Faust, 1992).
The thecal surface is smooth and covered with sparsely scattered large pores (Figs. 1-8). Marginal pores are present on both sides of the lipped cingulum (Figs. 1, 3). The thecal and marginal pores are either round (average diameter 0.3 µm) or oblong (average length 0.5 µm) (Figs. 4,8) and similar in appearance to the pores found in the cingulum (Fig. 7). All thecal pores (Fig. 8) and pores in the cingulum (Fig. 7) have smooth edges (Faust, 1992).
Thecal Plate Description:
The plate formula of Coolia monotis is: Po, 3', 7'', 6c, 6s, 5''', 2''''. On the epitheca a distinct oblong apical pore plate (Po), positioned off-center, is located adjacent to apical plates 1', 2', and 3' (Figs. 1,3,4). The Po is about 12 µm long, slightly curved and narrow, and bears a long slit-like apical pore. Two supporting costae border the slit-like pore. Surrounding the costae and apical pore are evenly spaced round pores (Fig. 4). The large Po is easily observed under LM and is useful for identification (Faust, 1992, Steidinger and Tangen, 1996).
The lipped cingulum is equatorial, narrow, and enclosed by lists with a smooth edge, similar in appearance to the intercalary bands (Figs. 1-3,5). The inner surface of the cingulum is lined with round pores (Figs. 3,6,7). On the ventral surface, a ventral pore is located on the right-hand ventral margin between apical plate 1' and precingular plate 6" (Fig. 5). The ventral pore has an ellipsoidal shape with an average diameter of 0.5 µm (Faust, 1992).
The sulcus is narrow, indented, and does not reach the antapex of the cell (Fig. 5). It has a deep chamber-like appearance with straight walls. Two slightly curved, wide, flexible lists partially cover the sulcus at two sides (Figs. 5,6), and a straight, narrow list is located on the antapical side (Figs. 5,6). The longitudinal flagellum is short, only 20 µm long, and emerges posteriorly from the sulcus (Fig. 6). This flagellum is often lost during fixation, though it can be observed in living populations (Faust, 1992).
Morphology and Structure:
Cells of Coolia monotis are photosynthetic, with many golden-brown discoid chloroplasts. Chloroplasts radiate from the center of the cell. C. monotis has one dorsally situated nucleus located in the hypotheca. A large, round pusule is also present adjacent to the sulcus that seems to open independently into the sulcus (Faust, 1992).
Reproduction:
Coolia monotis reproduces asexually by binary fission. Sexual reproduction has been documented for this species: gametes fuse and a planozygote is formed (Fig. 11) (see Faust, 1992).
Species Comparison:
Coolia and Ostreopsis species have morphological similarities and differences: 1.) the Po of C. monotis is similar in architecture, but considerably longer (12 µm) than in O. heptagona (8-9 µm) and O. ovata (6-7 µm); 2.) the ventral pore of C. monotis is located on the right-hand ventral margin between apical plate 1' and precingular plate 6" which is similar to the location of the ventral pore of O. ovata; and 3.) Coolia monotis has a relatively short (20 µm) longitudinal flagellum compared to other benthic dinoflagellate species, but it is significantly longer than the longitudinal flagellum of O. ovata (approximately 12 µm) (Besada et al., 1982, Faust, 1992, Norris et al., 1985).
Besada et al., 1982 suggested that mucilage secretion occurred through the ventral pore from the pusule of Ostreopsis species. This may also be true for C. monotis cells since they attach to the bottom of culture plates by mucus threads or are entwined in a veil of mucilage. Mucus formation prompted Besada et al., 1982 to consider a relationship between C. monotis, O. ovata and Gambierdiscus toxicus.
Coolia, Ostreopsis and Gambierdiscus also exhibit a similar internal anatomy (Besada et al., 1982) and sterol composition (Besada, 1982). Gambierdiscus toxicus, however, differs in having an additional sterol compound (Loeblich and Indelicato, 1986) possibly indicating a more distant relationship to the other two species.