Evseenko et al.: New data on the morphology of 7yphlachirus elongatus 
© MW646926 
© MW646930 
1 MW646927 
© MW646924 
1002 MW646928 
© MW646929 
© MW646925 
MK617131 Brachirus harmandi 
EF607337 Brachirus orientalis (China) 
@ MF611619 Brachirus orientalis (Bangladesh) 
100 @FOAE550-06 
FOAE551-06 
O GU673538 Dexillus muelleri 
HM422439 Brachirus sp. 
| Brachirus niger 
KU499833 Brachirus orientalis (N. Arabia) 
© KJ601760 Aseraggodes kobensis 
O UKFBI345-08 Heteromycteris japonicus 
MK617182 Brachirus annularis 
99 O JQ623997 Solea solea 
O KJ205297 Pegusa lascaris 
99 O FUT330-18 Soleichthys heterorhinos 
O JX501462 Zebrias japonicus 
2% 
HK 
Figure 6 
Neighbor-joining dendrogram created by using distances between mtDNA cyto- 
chrome c oxidase subunit 1 sequences calculated with Kimura’s 2-parameter 
substitution model, showing the discrimination by distance among species of 
the genus Typhlachirus, based on sequences from molecular analysis of spec- 
imens captured in the Mekong River delta in 2018 (grey circles), and closely 
related species of the genus Brachirus (black circles) and other representatives 
of the family Soleidae (open circles), based on sequences available in GenBank 
and the Barcode of Life Data System (BOLD). Bootstrap values (250%) are 
given above branches. GenBank or BOLD numbers are given for each sequence. 
and the review by Evseenko and Bolshakov (2018) were 
based on a small number of specimens of each species, 
which, in all probability, explains the registered differ- 
ences in meristic characters. 
We analyzed 88 specimens of T: elongatus from the 
Mekong River delta. The results indicate the homogene- 
ity of our sample (Figs. 5 and 6). In the examined speci- 
mens of T: elongatus, the range of fluctuations of meristic 
characters is very wide and can be seen not only from the 
ranges of minimum and maximum values but also from 
the interquartile ranges (Table 2). No clear direction in the 
changes in meristic characters associated with the growth 
of fish was revealed. Despite the large spread in the num- 
ber of rays in the dorsal and anal fins (D: 46—56; A: 33-43), 
the number of precaudal and caudal vertebrae, and the 
number of pores in the lateral line (PrCV: 8—10; CV: 23-27; 
LL: 84-108), our individuals form a homogeneous cloud 
(Fig. 5). Taking into account that PC1 explains a signifi- 
cant proportion of the total variability of the sample and is 
determined almost exclusively by the number of pores in 
the lateral line, the introduction of any apriori boundary 
Typhlachirus elongatus 
(or boundaries) for this characteristic 
between the assumed taxa would auto- 
matically lead to a clear division of the 
sample into 2 (or more) groups. Never- 
theless, such a division would be entirely 
artificial and would hide the objective 
primary result about the homogeneity of 
the sample. Results of molecular genetic 
analysis also indicate the absence of sig- 
nificant differences between specimens 
from the Mekong River delta. 
The range of meristic characters of 
blind sole from our sample is very broad 
and includes the values noted in the lit- 
erature for T: lipophthalmus, T. caecus, 
and T: elongatus. Several specimens of 
T. lipophthalmus and T. caecus turned 
up on the periphery of the cloud, which 
is mainly represented by our specimens, 
in the region of higher PC1 values (the 
number of pores in the lateral line) 
(Fig. 5). Typhlachirus elongatus from our 
sample had a pronounced morphologi- 
cal variability; therefore, it is essential 
to be careful about the taxonomic sepa- 
ration of specimens of the genus Typhla- 
chirus with the limiting values of one or 
another feature. Hence, we explain the 
extreme position of T: lipophthalmus 
and T: caecus in Figure 5 by the small 
number of specimens used in the anal- 
ysis. A similar broad range of meristic 
characters has been reported for some 
other species of Soleidae. For example, 
PrCV of 32-44 and LL of 90-133 have 
been suggested for zebra sole (Zebrias 
zebra) (Stephens, 2011) and PrCV of 
32-35 and LL of 82-121 have been sug- 
gested for B. panoides (Lapierre, 2007). Therefore, such 
a range of characters without support by other morpho- 
logical features cannot be a reason for the separation 
of species. As we noted earlier, the meristic characters 
of the 3 nominal species of Typhlachirus overlap, and 
extreme values were found even in specimens from the 
same sample. Accordingly, these characters cannot be 
used as diagnostic ones. 
The presence or absence of a pectoral fin on the right 
side of the body is noted in several works as an import- 
ant character and, in fact, the only character that distin- 
guishes T: lipophthalmus and T. elongatus from T: caecus 
(Hardenberg, 1931a; Pellegrin and Chevey, 1940; Evseenko 
and Bolshakov, 2018). According to their descriptions, 
T. lipophthalmus (Pellegrin and Chevey, 1940; Chabanaud, 
1948; Tan and Grinang, 2020) and T: elongatus (Pellegrin 
and Chevey, 1940; Evseenko and Bolshakoy, 2018) lack 
the pectoral fin on the ocular side of the body. All of our 
specimens have a pectoral fin on the right side of the body 
regardless of body length. However, it is not always visi- 
ble (sometimes presented as a skin outgrowth) or consists 
