Karlodinium ballantinum, Salas, 2008

4.3 Karlodinium ballantinum

Like Karenia View in CoL , Karlodinium species possess the characteristic straight apical groove but differ in the presence of a ventral pore on the epicone in most species and a unique type of amphiesma with plugs. Typical Karlodinium cells are small, globular rather than flattened like most Karenia View in CoL , and their straight versus sigmoid apical groove distinguishes them from the morphologically similar Takayama species ( Daugbjerg et al. 2000; de Salas et al. 2003). Most Karlodinium species share similar morphology and often overlap in size, shape, and diagnostic morphological characters. Species differentiation within this genus is based on cell shape, the presence/ absence of a ventral pore, the position of the nucleus, and the arrangement of chloroplasts. These characters are often difficult to distinguish in preserved samples but may be discerned by observing live cells (e.g., Bergholtz et al. 2006; de Salas et al. 2008).

Until recently, dinoflagellates belonging to the genus Karlodinium have not been recognized from Kuwait ’ s waters due to research being restricted to Lugol ’ s preserved samples and possible misidentification with other small gymnodinioid taxa. Five Karlodinium morphotypes have recently been reported from Kuwait based on the observations of live cells in freshly collected water samples ( Table 4), including Karl. australe , Karl. decipiens , Karl . digitatum (as Karenia digitata ), Karl. gentienii , and Karl. veneficum , as reported by Al-Yamani and Saburova (2019); however, no molecular data were provided for these species. In this study, two Kuwait strains, KW-JL-07 and KW-E9-046, exhibited the typical Karlodinium morphology, with small, nearly spherical to ellipsoidal cells, possessing a short straight apical groove, a large centrally located nucleus, and several elongated peripheral chloroplasts. The lack of a ventral pore in this species (as discerned by LM) sets it apart from most Karlodinium taxa previously reported in Kuwait, suggesting the finding of an unrecorded taxon. Among the currently described Karlodinium species, an inconspicuous or lacking ventral pore has been reported in Karl. antarcticum , Karl. ballantinum , Karl . digitatum, Karl. jejuense , and Karl. zhouanum ( de Salas et al. 2008; Li and Shin 2018; Luo et al. 2018; Siano et al. 2009; Yang et al. 2000). The cell morphology of Kuwait ’ s strains differed from that described in four out of five pore-lacking Karlodinium species in terms of shape (ellipsoidal instead of elongated in Karl. antarcticum ), nucleus position (centrally located nucleus versus those in the epicone in Karl. zhouanum or in the hypocone in Karl. antarcticum and Karl . digitatum), the apical groove length that extends for a short distance onto the dorsal epicone compared to its longer path (1/4 – 1/2 down the dorsal epicone) in Karl. antarcticum , Karl . digitatum, Karl. jejuense , and Karl. zhouanum , and the knob-like structures (microprocesses) lining the lower margin of the cingulum ( Figure 4G View Figure 4 ) have not been observed in other Karlodinium species. The morphology observed in Kuwait ’ s strains corresponds well with that described for Karl. ballantinum (Table 3). Although de Salas et al. (2008) originally reported this species as lacking a ventral pore, further SEM analysis by Benico et al. (2020) of strains from the Philippines and Japan revealed a pore or pore-like shallow depression in this species. As our morphological observations of this species were limited to light microscopy, further SEM examination is required to determine whether this character varies in Kuwait ’ s material.

The phylogenetic tree inferred from the LSU rDNA sequences in the present study also showed a high genetic similarity between the sequences obtained from Kuwait and the type material of Karl. ballantinum from Tasmania (Figure 5). Kuwait ’ s strains shared 98.19 – 99.27 % similarity (5 bp differences) with the holotype strain EF469232 View Materials . Through combined evidence from molecular phylogeny and morphology, this study reports the identification of K. ballantinum in Kuwait ’ s waters, marking the first record of this species in the entire Gulf.