Synchaeta vorax Rousselet, 1902

Min, Hee-Min Yang and Gi-Sik, 2022, New record of two marine synchaetid rotifers (Monogononta: Synchaeta) from Korea, Journal of Species Research 11 (3), pp. 174-179 : 176-178

Synchaeta vorax Rousselet, 1902 ( Figs. 1B , 2B , 4)

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Synchaeta vorax : Rousselet, 1902: 408 - 410.

Material examined. Korea, Incheon, Incheon Port (37° 27 ʹ 00 ʺ N, 126°39 ʹ 22 ʺ E), 31 Mar 2021, Hee-Min Yang. Voucher Number: NIBRIV0000895436 .

Diagnosis. Head large and wide. Apical field strongly convex. One tubular antenna on the center of apical field, tip of antenna with tuft. Four long styles present on apical field. Lateral auricles large, directed semi-cau- dally. Two small eyespots located near mastax. Head and trunk distinctly separated by wrinkled neck. Trunk cylindrical, tapered to posterior end. Longitudinal fold present on trunk. Lateral antennae at posterior third of trunk. Foot short, 60 - 65 μm in length. Pedal glands symmetrical and approximately the same length as the foot. Two small, separated toes on the foot. Total length 410 - 460 μm. Trophi virgate. Rami with frontal hook and several distinct teeth. One spine on middle of frontal hook. Each side of ramus teeth separated into two groups: three to four teeth on apical group and two teeth on basal group. Hypopharynx wide and crown-shaped. Manubrium straight and simple, with broad lamella. Fulcrum thick, machete-shaped.

Distribution. Cosmopolitan.

Remarks. The external morphological characteristics of Korean S. vorax specimens were most similar to the original description by Rousselet (1902). The trunk shape of the Korean specimens and the original description were slender and cylindrical, whereas those of Lie-Pettersen (1905) and Wilke et al. (2019) were plump and wineglass-shaped. In terms of trophi morphology, several variations were recorded in rami teeth. Wilke et al. (2019) reported that S. vorax has no distinct teeth and only a serrated plate. However, descriptions from Rousselet (1902), Lie-Pettersen (1905), and Arndt et al. (1990) indicated that the rami teeth of S. vorax possess several distinct teeth. The rami of the Korean specimen contained one frontal hook and distinctly large teeth. The teeth are divided into two groups as indicated in the ‘Diagnosis’ section, with each ramus containing three to four teeth on the apical group and two teeth on the basal group. The rami teeth formula of the Korean specimen was similar to that of S. curvata Lie-Pettersen, 1905 , described by Arndt et al. (1990). However, the two species are clearly distinguished by morphological characteristics such as the tubular apical antenna and the number of eyespots. Synchaeta vorax was recorded as a eurythermal species in a previous study ( Hollowday, 2002), and the Korean specimen was collected from November to March, at a water temperature of 5 - 10℃ and a salinity of 26.0 - 29.3‰.

Molecular analysis. Partial COI sequences were obtained from five specimens. The intra-specific genetic distances were 0.0 - 1.1% within the Korean population (657 bp) (GenBank accession numbers: ON038419 - ON038423). The genetic distances between the Korean and German S. vorax specimens were 11.1 - 12.4% (621 bp, Table 2) (GenBank accession numbers: MK905832 - MK905842) ( Wilke et al., 2020). These genetic distances were unusually large within the same species, even if they were in different population. Recently, as molecular analysis has been introduced to the rotifer research, cryptic species have been identified in various species ( GarcÍa-Morales and ElÍas-Gutiérrez, 2013; Obertegger et al., 2014; Papakostas et al., 2016; Kordbacheh et al., 2017; 2018). Most of the cryptic species are morphologically indistinguishable and have large genetic distance. In this regard, we reconfirmed the external and trophi characteristics of the Korean S. vorax specimens, and found no significant dif- ference from the previously known morphological characteristics. For the accurate assessment of biodiversity, the problem of cryptic species must be solved, and for this, it is considered that additional studies on biogeographical, ecological, and reproductive are needed in addition to morphological analysis.

Figures

Fig. 1. Line drawing of rotifers.A. Synchaeta grimpei. B. Synchaeta vorax. Scale bars: 100 μm.

Fig. 2. Optical microscopic images of rotifers.A. Synchaeta grimpei. B. Synchaeta vorax. Scale bars: 100 μm.