Pleurosigma pacificum, Du & Li & Xu, 2023

Du, Fei-Chao, Li, Yu-Hang & Xu, Kui-Dong, 2023, Morphology and molecular phylogeny of Pleurosigma pacificum sp. nov. (Pleurosigmataceae), a new tropical pelagic species from the Western Pacific Ocean, PhytoKeys 227, pp. 99-108 : 99

Pleurosigma pacificum sp. nov.

Fig. 1

Description.

Valves lanceolate, gradually tapering towards the subacute ends, 45.0-51.5 µm long and 13.0-15.6 µm wide (Fig. 1A-D ). Raphe filiform, straight, slightly curved near poles (Fig. 1A-D ). Raphe angle +2° to +4°. Valve center roundish (Fig. 1E , arrowhead). Terminal area funnel-shaped (Fig. 1F ). Transverse striae straight, parallel throughout, 21-22 in 10 µm, oblique striae 21-23 in 10 µm, intersecting at an angle between 32° to 35°.

In SEM, internally, raphe fissures terminate in helictoglossae at apices, orientated in opposite direction to one another (Fig. 1G, I , arrowhead). Internal central fissures straight, slightly expanded (Fig. 1H , arrowhead). Central nodule is raised and flanked by two central bars (Fig. 1H ). External central raphe fissures straight, simple (Fig. 1K , arrowhead). Terminal fissures bent to opposite side of valve, not extending onto valve mantle (Fig. 1L , arrowhead). Areolae loculate with external opening slits and internal poroids (Fig. 1G, J ).

Holotype.

MBMCAS286904, an example is illustrated in Fig. 1A, E, F . This slide was deposited in the Marine Biological Museum, Chinese Academy of Sciences, Qingdao, China.

Isotype.

MBMCAS286905, an example is illustrated in Fig. 1C . This slide was deposited in the Marine Biological Museum, Chinese Academy of Sciences, Qingdao, China.

Type locality.

7°0.26'N, 141°59.63'E, the upper 200 m water column in the tropical Western Pacific Ocean.

Etymology.

Named after the Pacific Ocean where the species was discovered.

Distribution and ecology.

Pleurosigma pacificum is a planktonic species known only from the type locality. The water temperature was 28.5 °C and salinity about 33.4 during sampling.

Gene sequences.

These sequences were deposited in the GenBank (SSU rDNA OQ437519, LSU rDNA OQ549922, rbc L OQ473490 and psb C OQ437519).

PhycoBank registration.

http://phycobank.org/103761.

Molecular phylogenetic analyses

The BLASTn search showed that the SSU rDNA sequence of P. pacificum shares 97.65% identity with an uncultured marine eukaryote (KC771201). The rbc L gene sequence of P. pacificum shares 92.54% identity with P. intermedium (NC_066077). The ML, BI and MP phylogenetic tree based on the concatenated SSU rDNA and rbc L gene showed that P. pacificum belongs to the clade of the genus Pleurosigma with high support (IQ-TREE ultrafast bootstrap value = 99, Mrbayes posterior probability = 1.00, MP standard boostrap value = 77 and MP jacknife value = 85). The P. pacificum is basal to all other species of Pleurosigma , and branched earlier than the two slightly sigmoid species, P. planctonicum and P. intermedium (Fig. 2 , Suppl. material 2).

Figures

Figure 1. A-F LM photographs of P. pacificum A-D cleaned frustules showing parallel transverse striae under LM E valve center showing a roundish central area (arrowhead) F funnel-shaped terminal area in apical position G-L SEM photographs of P. pacificum G internal view of the whole valve H internal valve central area showing straight, slight expanded raphe fissures (arrowhead) and nodule bordered by two arched bars I internal raphe fissures terminate in helictoglossae at the apices (arrowhead) J external view of the whole valve showing the terminal fissures curving into opposite directions K external central area of valve showing straight, simple raphe fissures (arrowhead) L terminal fissures (arrowhead). Scale bars: 10 μm (A-F); 5 μm (G, J); 1 μm (H, I, K, L).

Figure 2. Maximum likelihood (ML) and Bayesian inference (BI) phylogenetic trees based on the concatenated SSU rDNA and rbc L sequences. The values on each node indicate ML bootstrap and Bayesian posterior probabilities (%), respectively. Only bootstrap values over 50 % are shown on the tree. Black dot indicate ML / BI = 100 / 1.00. The asterisk indicates the topological incongruence between ML and BI trees.