Luticola halongiana Witkowski, M.Rybak, H-D.Nguyen & D-V.Nguyen, 2021

Rybak, Mateusz, Witkowski, Andrzej, Peszek, Lukasz, Kociolek, John P., Risjani, Yenny, Nguyen, Duc Hung, Zhang, Jinpeng, Yunianta,, Nguyen, Van Duy, Gastineau, Romain, Duong, Thi Thuy, Rosa, Philippe & Meleder, Vona, 2021, Marine and brackish Luticola D. G. Mann (Bacillariophyta) species from the Java Sea and South China Sea coasts with the description of three new species, PhytoKeys 183, pp. 115-142 : 115

Luticola halongiana Witkowski, M.Rybak, H-D.Nguyen & D-V.Nguyen sp. nov.

Figure 5

Description LM.

Valves rhombic-eliptic to rhombic-lanceolate with broadly rounded to slightly protracted apices in larger specimens, 9.9-22.1 μm in length and 5.4-7.7 μm in width (n = 30). Raphe filiform, slightly bent, axial area narrow, expanding into rectangular to bow-tie shaped central area bordered by 3-4 areolae. Stigma round, present near the valve margin. Transapical striae radiate throughout, 20-24 in 10 μm.

Description SEM.

Valve face flat, the transition from valve face to the mantle abrupt, marked with distinct hyaline stripe. Axial area narrow linear, slightly broadened towards the valve middle, expanding into the bow-tie shaped central area with slit like opening of stigma bordered by 3-4 small, rounded areolae. Raphe filiform and straight. Raphe branches very slightly bent with external proximal raphe endings strongly deflected to the valve primary side (opposite to stigma) with small, rounded grooves on the stigma-bearing side. External distal raphe ends slightly hooked and terminate on the apex valve mantle. The valve mantle bearing one row of oblong areola. Internally, raphe straight, with proximal endings slightly bent, and distal raphe endings terminating in small helictoglossae. Transapical striae composed by 3-4(5) round to slightly elongate areolae. Internally, areolae covered by hymen forming continuous strip. Internal stigma opening with circular lipped structure. Internally, longitudal channel visible, with small silica flap on site opposite to stigma.

Holotype.

slide SZCZ26472 stored in A. Witkowski Diatom Collection of the Institute of Marine and Environmental Sciences, University of Szczecin, represented here by Fig. 5I

Isotype.

Slide no. 2018/425 and unmounted material with the same number at the University of Rzeszów, Poland.

Type locality.

NE Vietnam: W South China Sea, Quáng Yên, in Halong region, oyster offshore aquaculture, 20°54'1"N, 106°54'17"E, leg. Vona Meleder and Philipp Rosa, 10th October 2018.

Etymology.

The specific epithet refers to the type location, Ha Long, NE Vietnam.

Distribution.

Species occur rarely, observed thus far at the type locality Quáng Yên in biofilm on shells, and on the north coast of Java in Indonesia, from periphyton from the plastic pier (slide SZCZ27006).

Taxonomic comment.

Luticola halongiana sp. nov. has a unique set of characters and it is difficult to point out any similar established species. The only exception is the position of the stigma, which is located almost in the middle between the valve center and valve margin. This makes it similar to L. madagascarensis , however, the latter species has external proximal raphe endings with long and distinct grooves on a side opposite the stigma; these grooves are indistinct in L. halongiana . Also, Luticola mutica ( Kützing) D.G.Mann shows some similarities to L. halongiana sp. nov. but it can be easily distinguished based on the narrower central area. Also L. mutica has areolae containing cribrum which is not present in described species.

Morphological characteristic of recently established Luticola taxa observed during this study.

Figures

Figure 5. LM micrographs of Luticola halongiana Witkowski, M. Rybak, H-D. Nguyen & D-V. Nguyen sp. nov. in size diminution series (A-Z). Holotype specimen - black frame I external view of frustule (AA-AC). Internal view of frustule (AD). Detailed external close-ups showing distal raphe ending (AE), proximal raphe endings with small rounded grooves and opening of stigma (AF). Detailed internal close-up showing distal and proximal raphe endings, hymen structure and stigma opening (AG). Scale bars: 10 µm (A-Z), 5 µm (AA, AB, AC, AD), 3 µm (AE, AG), 1 µm (AF).