Evseenko et al.: New data on the morphology of 7yphlachirus elongatus 115 
Vietnam 
Mekong River 
10°01’N 
105°02’E 105°26'E 
@, 
Hau River (Bassak) 
105°50’E 
! 
. 
"Qe. Cs 
‘es 
Co Chien River 
South China Sea 
106°14'E 106°38’E 
Figure 1 
Map of the distribution of the specific number of blind sole of the genus Typhlachirus (gray circles) 
collected in the delta of the Mekong River in Vietnam in 2018. Black dots indicate trawling loca- 
tions. The size of gray circles is related to the number of specimens captured. 
number of caudal vertebrae (CV), and number of pored 
scales on the horizontal branch of the ocular side lateral 
line, not including scales on caudal fin (LL). 
Statistical analysis 
To check the homogeneity of our sample of specimens 
across all studied features, principal component analy- 
sis was performed. On the basis of analysis of combined 
data (from our work and published reports) on T: elon- 
gatus, T. lipophthalmus, and T. caecus, we excluded from 
further analysis both the number of rays in the pectoral 
fins (because of the unreliability of data in the original 
descriptions) and the number of vertebrae (because of the 
partial lack of data). Results of a preliminary normality 
test (Shapiro—Wilk test) indicate that all the characters 
except the number of pores in the lateral line had distribu- 
tions that were not normal; therefore, we used Spearman’s 
rank correlation coefficients to find linear correlations 
between SL and other studied features. To ensure that we 
had not lost any information by using this nonparametric 
coefficient, we also calculated Pearson correlation coeffi- 
cients for our data set. To evaluate occurrence frequencies 
for each feature, the histograms for each character were 
built (Fig. 2). Principal component analysis was performed 
in PAST (vers. 2.17c; Hammer et al., 2001), and correlation 
analysis was done in R (vers. 4.0.3; R Core Team, 2020). 
Molecular analysis 
We extracted whole genomic DNA from muscle tissue of 
14 specimens of T: elongatus (Suppl. Table) (online only) by 
using the Diatom DNA Prep 100! kit (Izogen Laboratory, 
Moscow, Russia). In total, 650 base pairs from the barcode 
region of the mitochondrial cytochrome c oxidase subunit 
1 (CO1) gene were amplified with the primer set FishF1/ 
FishR2 (Ward et al., 2005). For the subsample of 8 speci- 
mens, we amplified the segment (574 base pairs) of the 16S 
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