A new species and a new combination in Protoperidinium sect. Oceanica (Peridiniales, Dinophyceae) from Vietnamese waters

In this study, we described and illustrated details of a new species, Protoperidinium vietnamicum sp. nov., from Vietnamese coastal waters and Protoperidinium curvicorne (Böhm) comb. Nov. is proposed as a new combination. Each cell's size range (length, width, and depth) was measured, and the morphological features of both species described here and selected related species in the Oceanica section were compared. In addition, the ecology and distribution of both species were given.

Methods
Sampling
These datasets were created from phytoplankton samples collected with vertical net hauls (mesh size – 25 µm and net diameter – 30 cm) at locations along Vietnamese coastal water, proven from associated projects in Vietnam.

Analyses
Take photographs:

Cells were observed by light microscopy (LM) and scanning electron microscopy (SEM). LM was performed using a Leica DMLB (Solms, Germany), and a digital camera DP71 (Olympus) was used for micro-photography. SEM was scanned on the Hitachi S4800 Field-Emission SEM (Hitachi Manufacturing Institute) at a voltage of 10.0 kV and a working distance of 8.3–9.2 mm. 

Biometric analyses:

Morphological measurements of cells from each photographed cell were carried out by light microscopy using imaging software (Standard cellSens ver. 3.1.1, Olympus, Tokyo, Japan).

The length (L) of the cell was measured from the epitheca's apex to the hypotheca's antapex.

The width (W) of the cell was measured directly in front of the cingulum or behind it, not including the cingular lists.

Depth (or height in some literature) (D) was measured in its widest part in lateral view, not including the cingular lists.

L/W ratio showing the variability in the cell size between Protoperidinium species section Oceanica.

Ecology and distribution:

Physical conditions such as temperature, salinity, and depth profile were measured at each sampling time using SeaBird 19 plus CTD (Sea-Bird Scientific, USA). Data from CTD were downloaded and processed using software from the manufacturer.

The GPS coordinates are collected at each station.

NA denotes missing values.

Comparison of the morphological biometrical characterizations:

The morphological characterizations of Protoperidinium species and the use of biometric terminology and abbreviations are as follows:

Apical horn: forms the apex of the cell and is formed by the apical plates.

Antapical horns: typically formed by antapical plates.

Cingulum: located approximately at the midpoint of the cell. When the cingulum is displaced, descending is the most common; the distal end is below the proximal end, which is always on the left side of the cell.

Sulcus: the longitudinal area on the ventral surface of the cell in Protoperidinium species, which is mainly in the ventral of the hypotheca.

The names of the thecal plates are abbreviated according to the Kofoid tabulation system as follows:

Intercalary plates (1a-3a) at epitheca do not touch the apex and the cingulum; the shape of the second anterior intercalary (2a) plate, such as quadra (four-sided), penta (five-sided), and hexa (six-sided).

Box plots:

Box plots were created by RStudio using the package "ggplot2" (Wickham, 2009). Wickham, H. (2009) Ggplot2: Elegant Graphics for Data Analysis. 2nd Edition, Springer, New York. https://doi.org/10.1007/978-0-387-98141-3.

本研究对采自越南近岸海域的新种越南原多甲藻（Protoperidinium vietnamicum sp. nov.）的细节进行了描述与图示，并提出新组合弯角原多甲藻[Protoperidinium curvicorne (Böhm) comb. nov.]。测定了单株细胞的尺寸范围（长度、宽度与厚度），对比了本次描述的两个物种与大洋组（section Oceanica）中选定近缘物种的形态特征。此外，还阐述了这两个物种的生态与分布情况。

## 方法
### 采样
本数据集源自越南近岸海域各站位的浮游植物样品，样品通过垂直拖网采集（网孔孔径25 µm，网口直径30 cm），相关样品来自越南境内的配套科研项目。

### 分析
1. 图像拍摄
采用光学显微镜（Light Microscopy, LM）与扫描电子显微镜（Scanning Electron Microscopy, SEM）对细胞进行观测。光学显微镜使用Leica DMLB型显微镜（德国索尔姆斯），搭配DP71型数码相机（奥林巴斯）进行显微摄影。扫描电子显微镜观测使用Hitachi S4800场发射扫描电镜（日立制作所），加速电压设定为10.0 kV，工作距离为8.3–9.2 mm。

2. 生物计量分析
利用成像软件（Standard cellSens ver. 3.1.1，日本东京奥林巴斯），通过光学显微镜对拍摄的每一株细胞进行形态学测量：
- 细胞长度（L）：从上壳（epitheca）顶端至下壳（hypotheca）后末端（antapex）的距离；
- 细胞宽度（W）：在沟带（cingulum）前方或后方测量，不包含沟带翼（cingular lists）；
- 细胞厚度（或部分文献中所称的高度，D）：在侧视图最宽处测量，不包含沟带翼；
- L/W比值：用于反映大洋组内各原多甲藻物种间的细胞尺寸变异情况。

### 生态与分布
采样时使用SeaBird 19 plus温盐深采水器（Conductivity, Temperature, Depth, CTD，Sea-Bird Scientific, 美国）测定各站位的水温、盐度与深度剖面等环境参数，CTD数据通过厂商配套软件下载并处理。
各采样站位均记录了GPS坐标。
缺失值以NA表示。

### 形态计量学特征对比
原多甲藻物种的形态特征描述以及生物计量学术语与缩写说明如下：
- 顶角（Apical horn）：由顶甲板构成，形成细胞顶端；
- 后角（Antapical horns）：通常由后甲板构成；
- 沟带（Cingulum）：大致位于细胞中点位置。若沟带发生偏移，最常见的形式为向下偏移，即远端端点低于近端端点，且近端端点始终位于细胞左侧；
- 纵沟（Sulcus）：原多甲藻细胞腹面的纵向区域，主要分布于下壳腹侧；
- 甲板命名依据科福德甲板命名系统（Kofoid tabulation system），缩写规则如下：
上壳的间插甲板（Intercalary plates, 1a–3a）不与顶端及沟带接触；第二前间插甲板（2a）的形状可分为四边形（quadra，四面）、五边形（penta，五面）与六边形（hexa，六面）。

### 箱线图绘制
箱线图通过RStudio结合"ggplot2"包（Wickham, 2009）绘制。Wickham, H. (2009) 《Ggplot2：优雅的数据可视化分析》，第2版，Springer，纽约。https://doi.org/10.1007/978-0-387-98141-3.