SPECIES DESCRIPTION

A total of 14 species of potentially toxic dinoflagellates associated with the leaves of T. testudinum were observed; these species belonged to two orders, three families and four genera. Among the genera present, Prorocentrum was the most representative during sampling, with a contribution of 50% of the species, which coincided with previous studies in other parts of the Caribbean (^{Valerio and Díaz, 2008}; ^{Almazán-Becerril et al., 2015}), followed by Ostreopsis with 21%. The numbers of species were similar between the two systems, with a difference of two more species in the bay. However, these differences were more evident in terms of composition. For instance, Coolia cf. malayensis, Coolia sp., Ostreopsis cf. lenticularis and Prorocentrum emarginatum were only observed in the bay, whereas Gambierdiscus sp. and Prorocentrum sp. 2 were found only in the lagoon (Table 1). In the bay, Prorocentrum lima, P. hoffmannianum and Ostreopsis cf. ovata were considered frequent species based on their appearances in all samples collected during both years, whereas Coolia sp., Gambierdiscus cf. caribaeus, Prorocentrum rhathymum and Prorocentrum sp. 1 were observed occasionally. In contrast, Prorocentrum sp. 1 was the most frequent species (79.17%) in the lagoon, followed by P. rhathymum (70.83%), whereas Gambierdiscus sp. And P. cf. concavum were found sporadically (Table 1). The species found are described below.

Table 1 Presence-absence and frequency (%) of the main species occurring in the 48 Thalassia testudinum samples obtained in Chengue Bay and Laguna between January 2014 and December 2015. 

Gambierdiscus cf. caribaeus Vandersea, Litaker, Faust, Kibler, Holland and Tester, 2009.

Description: Large cell (dorsoventral length: 82.7 ± 4.3 μm; transdiameter: 81.2 ± 6.7 μm; n = 4). The cell has a semicircular shape in both the apical and antapical views with a noticeable sulcus (Figure 2A, B and F). The U-shaped sulcus in the antapical view is deep and narrow (Figure 2B). The body is slightly compressed in the anteroposterior direction (Figure 2E). The surface is dense with small pores (Figure 2G). Plate 2’ is rectangular (length: 47 μm, width: 20-25 μm, Figure 2C), and plate 2’’’’ is pentagonal and wide (length: 50 μm, width: 37 μm, Figure 2B and D). Based on the observed structures, especially the shapes of plates 2’ and 2’’’’, and the descriptions by ^{Litaker et al. (2009)}, ^{Jeong et al. (2012)} and ^{Hoppenrath et al. (2014)}, the characteristics of the species coincide with those of G. caribaeus, although the cells of the present study were somewhat larger than those described by Litaker et al. (2009).

Figure 2 Micrographs of Gambierdiscus sp1 with optical microscope (A-E) and scanning electron microscope (SEM) (F-G). A-B. Cell in antapical view. C. Second apical plate (2’). D. Second antapical plate (2’’’’). E. lateral view. F. Antapical view in SEM. G. Detail of the pores that cover the cell. Po: apical pore. Scale bar (A-F) = 20 μm, (G) = 5 μm. 

Habitat: Usually circumtropical, commonly benthic, associated with various substrates including macroalgae, seagrass, sand and dead coral in protected areas of the waves and away from continental water inputs (^{Faust, 1995}; ^{Hallegraeff et al., 2004}; ^{Tester et al., 2014}). In case of disturbances, the organisms can swim by moving short distances (Hallegraeff et al., 2004).

Toxicity: Some species of the Gambierdiscus genus are the main producers of gambiertoxin and maitotoxin, which are toxins that cause ciguatera (^{Litaker et al., 2010}, ^{Parsons et al., 2012}, ^{Fraga et al., 2016}). The toxicity of this species has not been confirmed in Chengue; however, several cases of ciguatera were reported previously in the Colombian Caribbean, particularly in the departments of Magdalena, Bolívar and San Andres Island (^{Álvarez, 1997}, 1999; ^{Gaitán, 2007}; ^{Celis and Mancera, 2015}).

Gambierdiscus sp.

Description: Large cell (dorsoventral length: 76 μm; transdiameter: 70 μm; n = 1) that is compressed in the anteroposterior direction (Figure 3F). In apical view, the shape is more oblong than Gambierdiscus cf. Caribaeus, and the dorsal end of the cell is slightly acute (Figure 3B). A deep and wide U-shaped sulcus is evident in the antapical view (Figure 3B and D). The plate surface is covered with small pores (Figure 3H). The apical pore plate (Po) is displaced towards the ventral portion (sulcus). Plate 2’ is asymmetrical in the shape of an axe, and plate 2’’’’ is pentagonal, similar to the description by ^{Litaker et al. (2009)} and ^{Hoppenrath et al. (2014)} for G. polynesiensis. However, in the description of the authors, the dorsal end of the cell is not acute, and the dorsoventral length is shorter than the length observed in the present study. Additionally, there is no evidence of the presence of this species in the Caribbean.

Figure 3 Micrographs of Gambierdiscus sp. 2 with optical microscope (A-F) and SEM (G-H). A-B Antapical view. C-D sulcus. E. Apical plates and aplical pore (Po). F. Lateral view. G. Antapical view in SEM. H, Detail of the pores that cover cell plates. Scale bar (A-G) = 20 μm; (H) = 5 μm. 

Coolia cf. malayensis Leaw, P.-T. Lim and Usup, 2001.

Description: Small form (dorsoventral length: 29.9 ± 2.6 μm; transdiameter: 28.0 ± 2.4 μm; n = 18) that is rounded and slightly compressed in the anteroposterior direction with a lenticular shape (Figure 4D). In the lateral view, the epitheca shifts towards the dorsal portion, and the hypotheca is closer to the ventral area (Figure 4D) similar to the observations of ^{Gómez et al. (2016)}. The apical pore plate (Po) is visible under a light microscope and is located between plates 2’ and 4’ in the upper left apical position of the cell, with an approximate size of 6.7 μm (Figure 4A). The Po size is larger than the one reported by ^{Leaw et al. (2010)} and ^{Karafas et al. (2015)} (5.0 and 5.9 μm, respectively). Plate 4’ is oblong with a hexagonal shape and is located towards the center of the cell; its right edge makes contact with plate 5’’, which tends to be the largest of the epitheca (Figure 4A and G); this pattern is similar to the pattern observed in genus Ostreopsis. Plate 3’ is pentagonal and is located between plates 4’ and 3’’. Plate 3’’’ is rectangular, centered and wide and occupies much of the hypotheca (Figure 4C and H). The surfaces of the plates are covered with small pores (Figure 4G and H). The sulcus is narrow, with two membranes projecting out on each side (Figure 4B and C). The species resembles C. palmyrensis and C. monotis based on the shape and arrangement of plates 4’, 5’’ and 3’’’. However, C. palmyrensis is usually smaller in size, and its thecal plates have a lower pore density (Karafas et al., 2015). For C. monotis, the cells have a deep sulcus expanding to occupy almost a quarter of the cell, whereas in the organism observed here, the sulcus is short with an opening towards the base (Figure 4H). Coinciding with Leaw et al. (2010), plate 3’’’ is the largest of the hypotheca in C. malayensis, whereas in C. monotis plates 3’’’ and 4’’’ have similar sizes. However, other authors have observed similarity in plate sizes in both species (^{Jeong et al., 2012}; Gómez et al., 2016).

Figure 4 Micrographs of Coolia cf. malayensis under optical microscope (A-E) and SEM (F-H). A. Apical view. B-C. Antapical view (arrow indicates one of the sulcal membranes). D. Lateral view. E-F. Ventral view and sulcus details. G. Apical view In SEM. H. Antapical view. Po: Apical pore. Scale bar (A-E) = 20 μm, (F-G) = 5 μm, (H) = 10 μm. 

Habitat: Marine genus, subtropical and temperate waters. Coolia cf. malayensis has been associated with macroalgae, coral fragments and sand (^{Leaw et al., 2010}). The most studied species (C. monotis) has been observed in planktonic samples, brackish habitats, coastal lagoons and mangrove areas in shallow waters (^{Faust, 1992}; ^{Steidinger and Tangen, 1996}); however, its distribution is often limited to temperate zones.

Toxicity: Not confirmed in the study area; however, some species of the genus are potentially toxic. A few strains produce cooliatoxin, which is a potent neurotoxin that may lead to respiratory difficulties, and blockage of some nerves essential for the functioning of the nervous system has been confirmed in some mammals (^{Holmes et al., 1995}; ^{Rhodes et al., 2000}; ^{Fraga et al, 2008}). To date, the negative effect of this toxin has not been reported in humans.

Coolia sp.

Description: The cell is rounded and globular, and the epitheca is slightly compressed towards one end. Dimensions of single organism observed were as follows: dorsoventral length 38.89 μm and transdiameter 40.1 μm. The sulcus is even narrower than in Coolia cf. malayensis, with the presence of two small membranes projecting out on each side (Figure 5A). Unlike Coolia cf. malayensis, in the lateral view the epitheca and the hypotheca do not shift towards the ends (Figure 5B). We could not provide a more detailed description of the plates because only one cell was found in the samples. The specimen has an affinity with C. tropicalis and C. canariensis, mainly due to its size, which is larger than the other species of this genus and coincides with the sizes described by ^{Fraga et al. (2008)}, Mohammad-Noo et al. (2013) and ^{Karafas et al. (2015)}.

Figure 5 Micrographs of Coolia sp. under optical microscope. A. Antapical view (arrow indicates the two small membranes projecting out of the sulcus). B. Lateral view. C. Ventral view. Scale bar = 20 μm. 

Ostreopsis cf. ovata Fukuyo, 1981.

Description: The cells are oval, elongated and acute at their ventral ends, with a tear shape (Figure 6A- C). The cells are the smallest form of the genus among those observed in the samples, with a dorsoventral length of 66.2 ± 3.5 μm and a transdiameter of 39.9 ± 3.3 μm (n = 35). The anteroposterior axis is approximately equal to the width of the cell. The apical pore plate (Po) is narrow, with a length of approximately 9.7 μm, and is noticeably shifted dorso-laterally to the left of the apical zone, which increases the difficulty of observing plate 2’ (Figure 6B and D). The sutures between the plates are soft and poorly visible. The shape is similar to O. ovata; however, according to the descriptions by ^{Penna et al. (2005)}, the specimen differs from O. ovata in the shapes of plates 4’, 3’ and 2’’’’, which are similar to the plates observed in O. heptagona except for the suture indicated with the arrow in Figure 6D. In O. heptagona, the suture makes direct contact with plate 4’, whereas in the observed species, the suture makes contact with plate 3’. Both the sizes of the cells observed in the present study and the lengths of the Po are greater than those reported by ^{Faust et al. (1996)} and Faust (1999) for O. ovata. The morphological variability of this species is quite broad, and its taxonomic classification needs to be validated using the information available in genetic databases (Penna et al., 2005).

Figure 6 Micrographs of Ostreopsis cf. ovata observed under optical microscope. A. Apical view. B. Detail of the apical plates. C. Antapical view and plates details. D. Details of the plates sutures and of the apical pore complex (arrow indicates the suture between plates 3’ y 5’’ that separate 4’ y 4’’). Po: apical pore. Scale bar = 20 μm. 

Habitat: Ostreopsis ovata is a marine benthic species that may be attached to macrophytes and other substrates. This species is common in tropical, subtropical and temperate zones. However, O. ovata is often more frequent in warm waters (^{Parsons et al., 2012}). Ostreopsis sp. have occasionally been observed in planktonic samples.

Toxicity: The species has been recorded as a producer of various toxins, including ostreotoxins and palytoxins (^{Granéli et al., 2011}), which cause gastrointestinal, respiratory and dermatological problems in humans (^{Parsons et al., 2012}). However, its toxicity has not been confirmed in the study area.

Ostreopsis sp.

Description: The cells are ovoid and somewhat pointed towards the ventral portion and wide towards the dorsal end in the apical view. Dimensions: dorsoventral length: 84.8 ± 5.7 μm; transdiameter: 64.6 ± 5.5 μm (n = 37). Compressed dorso-ventrally, the thecal plates exhibit undulations that are evident in lateral view (Figure 7E) similar to the description by ^{Fukuyo (1981)} for O. siamensis. The thecal plates are covered by a single type of pores, which are located somewhat distant from each other and form a contiguous line in the outer margin of the precingular plates (Figure 7F). The apical pore plate (Po) is narrow and elongated (19.7 μm) with a curvature parallel to the upper left edge of the cell (Figure 7B, C and F). Considering the size of the cells observed, the length of the Po and the shape and arrangement of the thecal plates, the species could be O. labens (^{Faust et al., 1996}; ^{Hoppenrath et al., 2014}); however, according to the descriptions reported by some authors, the species does not present undulations in the plates. Due to their variability in size and shape, the cells observed may be part of a complex composed of more than one species. However, the taxonomic description of this genus is not very clear, and most of the characteristics overlap between species, making their differentiation very complex. ^{Penna et al. (2005)} indicated that high morphological variability could be observed between cells of the same species, and Almazán- Becerril et al. (2015) mentioned that the taxonomy of this genus was so ambiguous that differentiation between species was impossible.

Figure 7 Micrographs of Ostreopsis sp. under optical microscope (A-F) and SEM (G-I). A. Cell in antapical view. B. Detail of the apical plates. C. Apicales plates stained with calcofluor and view by epifluorescence. D-E. Internal view of the antapical plates. F. Apical pore (Po) and pores. G. Apical view in SEM. H. Detail of the apical poro plate (Po). I. Pores that cover the cell. Scale bar (A-E) = 20 μm, (G) = 10 μm), (H) = 2 μm, (I) = 5 μm. 

Ostreopsis cf. lenticularis Fukuyo 1981.

Description: The cell is rounded in the apical view (Figure 8A-C), lenticular and slightly pointed towards the sulcus. The cell is antero-posteriorly compressed and has larger size than the other species of this genus observed in the samples. Dorsal-ventral length: 102.1 ± 7.0 μm; transdiameter: 83.8 ± 6.4 μm (n = 24). The thecal plates have two types of pores (small and more abundant and thicker); both pore types are visible under a light microscope (Figure 8D). The Po is narrow and long (Figure 8A), with an approximate length of 22 μm. This specimen has the same pattern of plates as Ostreopsis sp.; however, apart from the size and presence of the two types of pores, O. cf. lenticularis is rounded and lacks thecal undulations, which coincides with the description by ^{Hallegraeff et al. (2004)}. ^{Faust (1996)} indicated that the presence of both types of pores occurred in O. siamensis, although ^{Fukuyo (1981)} and ^{Parsons et al. (2012)} agreed that this characteristic was typical of O. lenticularis. Additionally, the cell size and the length of the Po coincide with some of the characteristics described by Faust (1999) for O. marinus; however, the author indicated that the thecal surface of this species had small pores and not two types of pores, as was observed in the cells from Chengue.

Figure 8 Micrographs of Ostreopsis cf. lenticularis under optical microscope. A. View of apical region indicating the plates and the apical pore (Po). B-C. Internal view of the plates. D. Detail of the pores that cover the cell (arrows indicate the two different thecal pores). Scale bar (A-C) = 20 μm. 

Habitat: Benthic species attached to rocks and other substrates or epiphytes of macrophytes in shallow circumtropical waters (^{Hallegraeff et al., 2004}).

Toxicity: The species has been recorded as a potentially toxic producer of palytoxins and other analogous toxins (^{Tosteson et al., 1989}; ^{Ashton et al., 2003}; ^{Granéli et al., 2011}) that are harmful to some organisms, including humans. The toxicity of the species in the region has not been confirmed.

Prorocentrum hoffmannianum Faust, 1990.

Synonym: Exuviaella hoffmanniana (Faust) McLachlan, Boalch et Jahn1997. Exuviaella hoffmannianum (Faust) McLachlan et Boalch (^{Hoppenrath et al., 2014}).

Description: The cell has a broad, tear-like, oval shape that is somewhat narrower towards the apical area, with a flattening towards the center of the cell where the pyrenoids are located (Figure 9A). Dorsal-ventral length:

50.6 ± 3.1 μm transdiameter: 37.3 ± 2.4 μm (n = 38). The theca surface is reticulated-excavated (^{Hoppenrath et al., 2013}), and reniform pores are dispersed on the plates (Figure 9G) but absent in the center. The V-shaped periflagellar area has eight plates (1-8) (Figure 9J and K) and a wide adjacent apical collar (Figure 9C and F). Periflagellar plate 1 has three slits (Figure 9J and K) that coincide with the description by Hoppenrath et al. (2013). The morphology of these cells presents variations in shape and size, even some of them with a slightly reduced apical collar were observed. The species is easily confused with P. sabulosum, P. tropicalis and P. belizeanum, but ^{Herrera-Sepúlveda et al. (2015)} confirmed by molecular analysis that there was no difference between P. hoffmannianum and P. belizeanum. Regarding the other species, Hoppenrath et al. (2014) suggested that a more detailed analysis was needed to establish the boundaries that separated them.

Figure 9 Micrographs of Prorocentrum hoffmannianum under optical microscope (A-C) and SEM (D-J). A. View of the right plate. B. Right plate with pore detail. C. Left plate. D. Cell in ventral view. E. Dorsal view. F. Detail of the apical collar. G. Detail of pores and areoles covering the cell. H-J. Periflagelar área (apical). J. Periflagelares plates, numbered following^{Hoppenrath et al. (2013)}. Pr: pirenoid, pa: accessory pore, pf: flagelar pore. Scale bar (A-C) = 20 μm, (D-E) = 10 μm, (F-G) = 2 μm, (H) = 10 μm, (I) = 5 μm, (J-K) = 1 μm. 

Habitat: Marine species, benthic, widely distributed in tropical and subtropical areas, usually found on various substrates, such as sand, rocks or phanerogams (^{Chomérat et al., 2010}).

Toxicity: A potentially toxic species that is a producer of okadaic acid and its analogues, which generate DSP (^{Faust et al., 1999}; ^{Hoppenrath et al., 2013}).

Prorocentrum lima Stein, 1878.

Synonym: Cryptomonas lima Ehrenberg 1860.

Homotypic synonym: Exuviaella lima (Ehrenberg) Bütschli 1885, E. marina var. lima (Ehrenberg) Schiller 1931 (^{Guiry and Guiry, 2016}).

Heterotypic synonyms: Exuviaella marina Cienkowski 1881, Dinopyxis laevis Stein 1883, E. laevis (Stein) Schroder 1900, E. cincta Schiller 1918, E. ostenfeldi Schiller 1933, E. caspica Kiselev 1940, P. marinum Dodge et Bibby 1973 and Prorocentrum arenarium Faust 1994 (^{Guiry and Guiry, 2016}).

Description: The cell is ovoid, oval and oblong. Dorsoventral length: 40.4 ± 2.9 μm; transdiameter: 25.0 ± 2.0 μm (n = 42). In valve view, the cell is narrower towards the periflagellar area, ellipsoidal lenticulate in lateral view and slightly flattened towards the central portion, where prominent pyrenoids are internally located (Figure 10A), visible under the light microscope. The thecal surface is soft with small dispersed oval pores that form a marginal row and surround the periflagellar area (Figure 10C-F); the central portion of both thecal plates are devoid of pores (Figure 10B-D). The V-shaped periflagellar area with eight (1-8) plates adjacent to the flagellar pores (Figure 10G and H) coincides with the description of ^{Hoppenrath et al. (2013)}. The species presents a wide variability of forms and sizes, which sometimes generates misidentifications.

Figure 10 Micrographs of Prorocentrum lima under optical microscope (A-B) and SEM (C-G). A. Right theca. B. Right theca with pores. C. Right theca. D. Left theca. E-G. Periflagelar area (apical). G. Periflagelar plates, numbered following^{Hoppenrath et al. (2013)}. Pr: pirenoid, pa: accessory pore, pf: flagelar pore. flagelar. Scale bar (A-B) = 20 μm, (C and E) = 10 μm, (D) = 5 μm, (F) = 2 μm, (G-H) = 1 μm. 

Habitat: Marine species, epibenthic, embedded in sandorattachedtovarioussubstrates, includingmacrophytes. Widely distributed in tropical waters (^{Hoppenrath et al., 2013}, 2014). ^{Fukuyo (1981)} observed when performing cultures of this species that it normally adhered to the walls of the vessel, and cells were rarely found swimming freely. However, the species has been observed sporadically and in low densities in planktonic samples (^{Vila et al., 2001}, ^{Levasseur et al., 2003}).

Toxicity: No toxicity has been confirmed in the study area. However, the species is considered potentially toxic and produces okadaic acid and other congeners that may cause diarrheic shellfish poisoning (DSP) (^{Murakami et al., 1982}; ^{Lee et al., 1989}; ^{Torigoe et al., 1988}).

Prorocentrum emarginatum Fukuyo, 1981.

Description: The cell is asymmetric, rounded, slightly oval and slightly less broad towards the apical end (Figure 11A-D and F-G). In the lateral view, the thecal plates are slightly compressed dorsoventrally. Dorsoventral length: 36.7 ± 2.0 μm; transdiameter: 32.0 ± 1.5 μm (n = 8). The thecal texture is smooth with two types of pores in rows (Figure 11E) that are arranged radially from the periphery towards the center of the cell and are not completely present in the central portion of the theca (Figure 11C, D and F). A strongly marked V-shaped periflagellar area is observed (Figure 11B-C and F-G). In ventral view, it can be observed that the two apical shoulders are unequal, with the dorsal blunt and the ventral long and pointed (Figure 11 B-C and F), coinciding with the description of ^{Hoppenrath et al. (2013}, 2014). In the periflagellar area, a wing or spine-shaped structure protrudes from periflagellar plate 1 (Figure 11F and G). The species may be confused with Prorocentrum fukuyoi and P. scuptile; however, unlike P. fukuyoi, the cells observed do not have small pores in the center of the theca or possess a reticulated- excavated thecal surface as described for P. scuptile, which coincides with the description of P. emarginatum by Hoppenrath et al. (2013). However, a more detailed review at both the morphological and molecular levels is required to establish a clear difference between these three species and to understand the variability of the different characteristics.

Figure 11 Micrographs of Prorocentrum emarginatum under optical microscope (A-D) and SEM (E-G). A-B, Right theca. C. Right theca slightly showing the pore pattern. D. Left theca. E. Detail of the two types of thecal pores (white arrows). F. Ventral view. G. Detail of the periflagelar area and of the apical wing. Scale bar (A-D) = 20 μm, (E) = 5 μm, (F) = 10 μm, (G) = 2 μm. 

Habitat: Epibenthic marine species common in Caribbean waters. ^{Faust et al. (1999)} recorded this species in low densities on sediment, such as rocks or dead coral, attached to macrophytes and even on floating material.

Toxicity: The toxicity of this species has not been confirmed, although its presence has been associated with other benthic toxin-producing dinoflagellates (^{Faust et al., 1999}).

Prorocentrum rhathymum Loeblich III, Sherley and Schmidt, 1979.

Description: Cell with asymmetric shape, oval and oblong. Dorsoventral length: 32.1 ± 3.8 μm; transdiameter: 22.4 ± 2.0 μm (n = 5), with pyrenoids present (Figure 12A). The texture of the thecal surface is soft and presents a characteristic pore pattern with a row of apical pores and some rows of radial pores towards the posterior end (Figure 12C and D). The central portion of the theca is devoid of pores (Figure 12C). A narrow U-shaped periflagellar area is observed; one end of periflagellar plate 1 extends as a spine projecting towards the right apical end of the cell (Figure 12A-B and D). There is controversy surrounding the taxonomy of this species because in some studies, Prorocentrum rhathymum has been considered synonymous with P. mexicanum (^{Faust, 1990}, ^{Steidinger and Tangen, 1996}, Faust and Gulledge 2002), whereas in other studies it has been defined as a separate species (^{Cortés-Altamirano and Sierra-Beltrán, 2003}). However, in a recent study based on morphological and molecular analyses, ^{Gómez et al. (2017)} confirmed that these were the same specie.

Figura 12 Micrographs of Prorocentrum rhathymum under optical microscope. A-B. Right theca view (arrows indicate the apical spine). C. Left theca view and pore patern. D. Separation of the two thecas, cytoplasmic material in the center. Pr: pirenoid. Scale bar (A-D) = 20 μm. 

Habitat: Marine species, epibenthic, common on macroalgae and other substrates. This species is widely distributed in tropical and temperate waters (^{Hallegraeff et al., 2004}).

Toxicity: Potential toxin-producer. ^{Bomber and Aikman (1989)} recorded the presence of hemolytic toxins in cultures of the species. No toxicity has been confirmed in the sampling area.

Prorocentrum cf. concavum Fukuyo, 1981

Description: The cell is wide with a rounded ovoid shape that is somewhat narrow towards the apical portion (Figure 13). Dorsoventral length: 44.9 ± 0.6 μm; transdiameter: 39.3 ± 1.3 μm; (n = 3), with the presence of pyrenoids (Figure 13A and B). The thecal surface is reticulated-excavated with pores, absent in the center of the thecal plates (Figure 13D) and become denser towards the margins of the cell. The periflagellar area is noticeably pronounced towards the V-shaped lateral ends (Figure 13A and B). It was not possible to perform a more detailed study of the organism to confirm the species because only one pair of cells was observed in the samples.

Figure 13 Micrographs of Prorocentrum cf. concavum under optical microscope. A-C. Right theca. D. Right theca with thecal pores. Pr: pirenoid. Scale bar = 20 μm. 

Habitat: Marine organism, often associated with macroalgae and sediment (^{Faust et al., 1999}) both in the Pacific (^{Fukuyo, 1981}) and in the Caribbean (^{Valerio and Díaz, 2007}; ^{Almazán-Becerril et al., 2015}).

Toxicity: P. concavum has been shown to be capable of producing potent toxins, including okadaic acid and some undefined ichthyotoxic compounds (^{Bomber and Aikman, 1989}; ^{Dickey et al., 1990}; ^{Faust et al., 1999}), but the toxicity of this organism has not been verified in the sampling area.

Prorocentrum sp. 1

Description: The cell is symmetric, oblong oval and occasionally rounded. Dorsoventral length: 41.0 μm ± 2.3; transdiameter: 33.8 μm ± 2.4 (n = 24), with pyrenoids present (Figure 14). The texture of the plate surface is smooth, with small pores arranged irregularly that are difficult to observe under a light microscope (Figure 14D- F). The U-shaped periflagellar area is not very pronounced. Similar to P. cf. concavum, but differs in the cells size, pores patern (Figure 14D-F) and in the periflagellar area, which is wider in P. cf. concavum. A more detailed study of the organism is necessary to determine which species it belongs to.

Figure 14 Micrographs of Prorocentrum sp1 under optical microscope. A. Right theca. B. Detail of a cell attached to a particle (arrow indicating mucus). C. Lateral view of a cell attached to detritus. D. Ventral view. E. Right plate. F. Detail of the thecal surface with small pores. Pr: pirenoid. Scale bar = 20 μm. 

Prorocentrum sp. 2

Description: The cell is asymmetric with an oval oblong shape. Dorsoventral length: 47.0 μm ± 1.0; transdiameter: 32.0 μm ± 1.6 (n = 8), bean-shaped. The right margin is rounded, and the left margin shows a curvature towards the center of the cell. The thecal surface is soft-textured, with several rows of radial pores towards the posterior end of the cell. The V-shaped shallow periflagellar area has an elongated protruding apical spine that is not always visible in all cells because it appears to lie horizontally over the periflagellar area (Figure 15A and E). The species presents characteristics similar to those of P. rhathymum and P. shikokuense but differs from these species in their shapes and sizes; the cell is much larger than P. rhathymum, which does not have the curvature to the left end of the cell. Compared to P. shikokuense, the difference in the pore pattern is clear. In the cells observed in the present study, the wide striated intercalary band described by Su-^{Myat and Koike (2013)} was not detected. A more detailed study of the organism is necessary for identification at the species level. We could not obtain further information due to its low frequency in the samples during the sampling period.

Figure 15 Micrographs Prorocentrum sp. 2 under optical microscope. A-B, Righ theca. C. Right theca with pore pattern. D, Lateral view. E. Separation of the two thecas, arrow indicates apical spine. Scale bar = 20 μm.