Evseenko et al.: New data on the morphology of 7yphiachirus elongatus 
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rRNA gene by using the primer set 16Sar/6Sbr (Palumbi, 
1996). The choice of molecular markers was determined by 
the widest taxonomic representation of Soleidae species in 
the available databases. 
Polymerase chain reaction products were purified and 
sequenced bidirectionally by using the same primers and 
an Applied Biosystems BigDye Terminator v3.1 Cycle 
Sequencing Kit (Thermo Fisher Scientific Inc., Waltham, 
MA) with an Applied Biosystems 3730 Genetic Analyzer 
(Thermo Fisher Scientific Inc.). All sequences were edited 
and aligned by using Geneious, vers. 9.1.8 (Kearse et al., 
2012), to obtain consensus sequences and check the occur- 
rence of deletions, insertions, and stop codons. Haplo- 
types were defined by using FaBox (Villesen, 2007) and 
then were deposited in GenBank (National Institutes 
of Health, available from website) under the follow- 
ing IDs: MW646924-MW646930 (CO1 haplotypes) and 
MW648330—-MW648332 (16S rRNA haplotypes). Indices 
of diversity (number of polymorphic [segregating] sites, 
the nucleotide diversity, and the haplotype diversity; Nei, 
1987) were calculated for the mtDNA CO1 gene by using 
DnaSP software, vers. 6.0 (Rozas et al., 2017). Tajima’s D 
(Tajima, 1989) and Fu and Li’s F (Fu and Li, 1998) tests of 
neutrality also were performed with DnaSP. 
Distances between mtDNA CO1 sequences were calcu- 
lated by using MEGA, vers. 6.0 (Tamura et al., 2013), under 
Kimura’s 2-parameter substitution model commonly used 
for DNA barcoding in studies of fish species (Ward, 2009). 
A neighbor-joining (Saitou and Nei, 1987) dendrogram 
with 1000 bootstraps was created by using distances, cal- 
culated with Kimura’s 2-parameter substitution model, in 
MEGA to provide a graphic representation of the diver- 
gence patterns among Typhlachirus and closely related 
species of Soleidae. We used sequences of 4 species of the 
genus Brachirus—B. annularis, B. harmandi, the black 
sole (B. niger), and the oriental sole (B. orientalis)—the 
tufted sole (Dexillus muelleri), Aseraggodes kobensis, the 
bamboo sole (Heteromycteris japonicus, the Atlantic sole 
(Pegusa lascaris), the wavyband sole (Zebrias japonicus), 
the common sole (Solea solea), and the tiger sole (Soleich- 
thys heterorhinos) from GenBank and the Barcode of Life 
Data System (BOLD Systems, available from website). 
Additionally, for measuring intraspecific and interspecific 
divergence, uncorrected p distances, meaning the propor- 
tions of nucleotide sites at which 2 sequences being com- 
pared are different, were calculated in MEGA by dividing 
the number of nucleotide differences by the total number 
of nucleotides compared. 
Results 
Typhlachirus elongatus Pellegrin and Chevey, 1940 
Typhlachirus elongatus Pellegrin and Chevey, 1940:155 
(Fig. 1) (first description based on 2 specimens). Mekong 
River delta. Syntypes (2): MNHN 1939-0270 (2). Rain- 
both, 1996:222 (listed). Desoutter et al., 2001a:328 (listed). 
Evseenko and Bolshakov, 2018:553 (description). Tan and 
Grinang, 2020:7 (fishing localities). 
Brachirus elongatus: Munroe in Randall and Lim, 
2000:646 (listed). Kottelat, 2013:464 (listed). 
The description of the morphology of T: elongatus is 
somewhat scattered; therefore, it is advisable to give a 
short but complete description here. 
Key diagnostic features 
D: 46-55, A: 33—40, C: 10-13, P1,: 3-6, P1,: (0)1-3, P.: 3, V: 
32-36, PrCV: 8-10, CV: 23-27, LL: 84-108 (Table 1). The 
body is right-sided, broad in front, tapered toward the tail, 
and strongly compressed (Fig. 3). All specimens have a 
right eye, but it is reduced in varying degrees. Gill rakers 
are absent from the gill arches. The mouth is curved to 
Table 1 
Meristic characters and proportional measurements of the Mekong blind sole (Typhlachirus elongatus) caught in the 
Mekong River delta in 2018 (number of specimens [n]=85) and from Evseenko and Bolshakov (2018) (n=3) in different 
size classes based on standard body length (SL). Features include number of rays in dorsal fin (D), number of rays in anal 
fin (A), number of rays in caudal fin (C), number of rays in pectoral fin on the ocular (right) side of the body (P1,) and 
on the blind (left) side (P1,), number of pored scales on the horizontal branch of the ocular side lateral line not including 
scales on caudal fin (LL), number of precaudal vertebrae (PrCV), number of caudal vertebrae (CV), number of vertebrae 
(V), body depth at pectoral fin base (BD), and head length (HL). 
SL 
(mm) 
14-20 
21-30 
31—40 
41-50 
51-60 
61-70 
71-80 
