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are as follows: T: elongatus differs from T: caecus in a more 
elongated body shape, a more curved mouth, the shape of 
the nostril, the absence of pectoral fins, and coloration, and 
T. elongatus differs from T: lipophthalmus in coloration and 
smaller scales (Pellegrin and Chevey, 1940). Typhlachirus 
caecus differs from T: lipophthalmus in the presence of 
pectoral fins (Hardenberg, 1931a). In his revision of blind 
soles, Chabanaud (1948) carefully studied the external 
morphology, anatomy, and osteology of all specimens avail- 
able at that time (8 specimens). He noted that there were 
no sufficient reasons to distinguish these 3 species and 
combined them into one monotypic genus Typhlachirus. 
As a species epithet, he proposed to keep the earlier syn- 
onym T: lipophthalmus (Chabanaud, 1939), suggested by 
Karoli (1882). 
This revision (Chabanaud, 1948) had been unknown to 
subsequent researchers until, in 2018, we published a work 
on the morphology of blind soles with a historical review 
of taxonomic changes in the genus Typhlachirus (Evseenko 
and Bolshakov, 2018). At the time of that writing, only 2 spe- 
cies had been recognized as valid: T: caecus and T. elonga- 
tus (Munroe, 2000; Desoutter et al., 2001a; Lapierre, 2007; 
Kottelat, 2013). However, to identify our specimens, we 
compared them with all species of the genus Typhlachirus 
known at that time, including the unaccepted T: lipophthal- 
mus (Evseenko and Bolshakov, 2018). The purpose of the 
Evseenko and Bolshakov (2018) article was to discuss the 
problems of the taxonomy of blind soles and supplement 
the data on their morphology. However, in Eschmeyer’s Cat- 
alog of Fishes, the work has been interpreted as a revision of 
the genus Typhlachirus. As a result, all 3 types of blind soles 
are currently indicated as valid in that database (Fricke 
et al., 2021), and the Chabanaud (1948) revision mentioned 
in the article (Evseenko and Bolshakov, 2018) was not taken 
into account again. 
During an expedition to the estuarine part of the 
Mekong River delta, we caught 85 new specimens of blind 
soles. When trying to determine the species involved, we 
found that the diagnostic features from the first descrip- 
tions and other available literature on these species did 
not allow the separation of species of Typhlachirus. The 
range of meristic characters of the new specimens is much 
more extensive than have been noted for T: elongatus. In 
addition, a pectoral fin was found in all new specimens. 
Given that the absence of a pectoral fin has been reported 
as a diagnostic feature for T: elongatus, the presence of one 
in our specimens prompted us to reexamine the specimens 
of T: elongatus studied in our previous work (Evseenko 
and Bolshakov, 2018), and it also served as a reason for a 
more thorough study of the new specimens. 
The primary purpose of the work reported here was 
to examine the diagnostic characters used to identify 
species of the genus Typhlachirus and to correct mis- 
understandings that appeared after the publication of 
Evseenko and Bolshakov (2018). Because there is no 
molecular genetic information for the genus Typhlachi- 
rus, we set out to fill this gap by using DNA barcoding, 
a tool widely used for identification of species and rapid 
assessment of their genetic variability (Hebert et al., 
2003; Hajibabaei et al., 2007; Crawford et al., 2013; 
Chambers and Hebert, 2016). 
Materials and methods 
The materials for this work were 85 specimens of juveniles 
and adults of the genus Typhlachirus, with a range in stan- 
dard body length (SL) of 14-80 mm (Suppl. Table) (online 
only), collected in the Mekong River delta (Fig. 1): 2 speci- 
mens (sp.) 32 mm SL, 32 mm SL, 6 April 2018, trawl no. 1, 
Co Chien River, 10°15’33”N, 105°57’46”E; 9 sp. 22-36 mm 
SL, 8 April 2018, trawl no. 5, Co Chien River, 10°10’50’N, 
106°10’22”E; 2 sp. 30 mm SL, 52 mm SL, 17 April 2018, 
trawl no. 4, Tien River, 10°19’48’N, 106°17’38”E; 4 sp. 
25-76 mm SL, 17 April 2018, 10°20’17”N, 106°19’60’E; 
5 sp. 24-49 mm SL, 17 April 2018, trawl] no. 1, Tien River, 
10°19’37’N, 106°17'37”E; 1 sp. SL? (a question mark [?] 
means that the length data were lost), 17 April 2018, 
10°19’80”N, 106°17’37’E; 2 sp. SL?, 4 August 2018, Tien 
River, 10°19’27”N, 106°00’50”E; 1 sp. SL?, 18 April 2018, 
10°19’2’”N, 106°10’12”E; 4 sp. 14-44 mm SL, 19 April 2018, 
trawl no. 1, Tien River, 10°19’19”N, 106°00’59”E; 1 sp. SL?, 
11 April 2018, 10°17’23”N, 106°34’11”E; 1 sp. 46 mm SL, 
24 April 2018, trawl no. 2, 10°16’26”N, 106°43’40”E; 1 sp. 
SL?, 11 May 2018, Tien River, 10°16’46”N, 10°50’55”E; 
3 sp. SL?, 12 May 2018, Ham Luong River, 10°14’22’”N, 
106°13’40”E; 1 sp. 54 mm SL, 15 May 2018, trawl no. 4, 
Ham Luong River, 10°06’23”N, 106°24’13”E; 1 sp. 60 mm 
SL, 17 May 2018, trawl no. 4, Ham Luong River, 9°56’26”N, 
106°39’20”E; 2 sp. 23 mm SL, 48 mm SL, 19 May 2018, 
trawl no. 2, Ham Luong River, 10°02’45”N, 106°27'27”E; 
4 sp. 30-58 mm SL, 21 May 2018, trawl no. 2, Ba Lai 
River, 10°08’50’N, 106°37'57”E; 1 sp. 80 mm SL, 23 May 
2018, trawl no. 1, Ba Lai River, 10°08’10’N, 106°39’00”E; 
1 sp. SL?, 24 May 2018, 10°07’18”N, 106°48’26”E; 39 sp. 
14-64 mm SL (capture data lost). 
To study the structure of the shoulder girdle and the 
degree of reduction of the pectoral fins, the 49- and 
53-mm-SL specimens were stained with alizarin and 
alcian blue and clarified according to the standard pro- 
cedure (Taylor and Van Dyke, 1985). Radiographs were 
made and studied for almost all specimens. For compar- 
ison, we used X-rays of 2 syntypes of T: elongatus 28 and 
33 mm SL, MNHN 1939-0270 (provided by the Muséum 
National d’Histoire Naturelle); 2 paratypes of T: caecus 76 
and 83 mm SL, MNHN 1942-0080 (in Chabanaud, 1948); 
and 1 specimen of T: lipophthalmus 61 mm SL, ZRC 59653 
(in Tan and Grinang, 2020). Additionally, 3 specimens, 59, 
67, and 71 mm SL, described in Evseenko and Bolshakov 
(2018), were studied. 
Information for the following features are included in 
the descriptions: SL, head length (HL), body depth at pec- 
toral fin base (BD), number of rays in dorsal fin (D), num- 
ber of rays in anal fin (A), number of rays in pectoral fin on 
the ocular (right) side of the body (P14), number of rays in 
pectoral fin on the blind (left) side (P1,), number of rays in 
pelvic fin (P2), number of rays in caudal fin (C), number of 
vertebrae (V), number of precaudal vertebrae (PrCV), 
