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Fishery Bulletin 120(2) 
Table 4 
Meristic characters and body proportions for 3 species of the genus Typhlachirus based on data from the 
literature on all known specimens of T: lipophthalmus, T. caecus, and the Mekong blind sole (T: elonga- 
tus) (Chabanaud, 1948; Hardenberg, 1931a; Pellegrin and Chevey, 1940; Tan and Grinang, 2020). Features 
include standard body length (SL), 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 
Species (mm) 
T. lipophthalmus 76 
T. elongatus 
of only 1 ray immersed under the skin (this ray becomes 
noticeable only after staining) (Figs. 3 and 4). 
This fact prompted us to reexamine 3 specimens of T: elon- 
gatus described in Evseenko and Bolshakov (2018). On each 
of these specimens, we found a pectoral fin presented as a 
skin outgrowth that did not exceed the size of scales found 
in all specimens (Fig. 4A). The rays in the fins of these spec- 
imens became clearly visible only after staining with aliza- 
rin. In all likelihood, authors who pointed to the absence of 
the pectoral fin (Karoli, 1882; Pellegrin and Chevey, 1940; 
Tan and Grinang, 2020) did not notice the fin, or it was 
reduced to a greater degree than in the specimens we exam- 
ined. Chabanaud (1939) also noted that the number of rays 
in the pectoral fin varied even in specimens from one sam- 
ple. He thought that the degree of development of a pectoral 
fin depends on the age or sex of the fish. We suggest that the 
presence or absence of a pectoral fin and the number of rays 
in it are not species-specific features for blind soles but are 
demonstrations of individual variability. 
We studied and compared all available X-rays of blind 
sole and found no difference between them. It should be 
noted here that some of the type specimens have been lost: 
the location is unknown for the holotype and 2 paratypes 
of T: caecus and the holotype of T: lipophthalmus (Fricke 
et al., 2021). On the basis of the X-ray of the paratype of 
T. caecus and non-type T: lipophthalmus, we measured the 
proportions of the body (BD and HL) and meristic charac- 
ters (D, A, C, and V). We found that they were within the 
range of proportional measurements and characters of the 
studied collection of T: elongatus. 
The body coloration of these 3 blind sole species varies 
somewhat but is generally similar (Karoli, 1882; Harden- 
berg, 1931a; Pellegrin and Chevey, 1940; Evseenko and 
NOBPNKHKWOCTOC SO 
LL PrCV CV Vv 
AanarPE Doo a»w#4n4 
Bolshakov, 2018; Tan and Grinang, 2020). Slight varia- 
tions in fish colors may be due to phenotypic plasticity 
or fixation—the difference is visible in photographs 
between the fresh and fixed specimens (Tan and Grinang, 
2020). Additionally, characteristics of the substrate, food 
items, season, and sex can influence color differences. 
Noticeable variations in coloration have been reported 
for B. aspilos from different localities, and the authors 
suggest that these differences do not depend on sex but 
on the substrate (Okamoto and Motomura, 2021). 
It turns out that the only thing that can be used as 
a diagnostic feature is the place of capture. However, it 
should be taken into account that all 3 locations where 
the type material were caught are in coastal waters of the 
South China Sea. The early developmental stages of blind 
soles are unknown. However, with a few exceptions, most 
soles have pelagic eggs and larvae (Ahlstrom et al., 1984), 
which are freely carried by currents and settle on suitable 
substrates. There is no geographical boundary between the 
regions where the type specimens were caught (Morimoto 
et al., 2000; Qu, 2000). Therefore, the 3 nominal species of 
blind sole may be local populations of the same species. 
Conclusions 
We analyzed our materials and found that the features 
thought to be diagnostic do not work for separating the 
3 species of Typhlachirus. All the described interspecific 
differences are within the range of variation found in our 
specimens from the Mekong River. The pectoral fin on the 
ocular side of fish of the genus Typhlachirus is a reduc- 
tion feature; results of data analysis for the combined 
