113 
National Marine 
Fisheries Service 
NOAA 
Fishery Bulletin 
@ established in 1881 << 
Spencer F. Baird 
First U.S. Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Abstract—The results of analysis of 
88 specimens of the Mekong blind sole 
(Typhlachirus elongatus) from the 
Mekong River delta in Vietnam indi- 
cate that the range of variability in 
meristic diagnostic characters of this 
species is broader than previously doc- 
umented. Comparison of the new mor- 
phological data for T: elongatus from 
our analysis with data from the avail- 
able literature for T: lipophthalmus and 
T. caecus reveals no differences between 
species. This fact confirms Chabanaud’s 
conclusions about the monotypy of the 
genus Typhlachirus and indicates the 
need for further revision of the genus. 
Here, molecular data from the genes 
cytochrome c oxidase subunit 1 and 16S 
rRNA are presented for the first time 
for the genus Typhlachirus. 
Manuscript submitted 19 November 2021. 
Manuscript accepted 18 March 2022. 
Fish. Bull. 120:113-124 (2022). 
Online publication date: 1 April 2022. 
doi: 10.7755/FB.120.2.2 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
New data on the morphology of the Mekong 
blind sole (Typhliachirus elongatus) indicating the 
need for a revision of the genus 
Sergei A. Evseenko (deceased)' 
Dmitry V. Bolshakov' 
Yana Yu. Bolshakova (contact author)' 
Yuri O. Kopylov-Guskov”? 
Natalya V. Gordeeva'” 
Evgeniia P. Karpova?’® 
Alexander R. Boltachev (deceased)*° 
Email address for contact author: yanusrunaa@mail.ru 
' Shirshov Institute of Oceanology 
Russian Academy of Sciences 
36 Nakhimovsky Prospekt 
Moscow 117997, Russia 
? Lomonosov Moscow State University 
Leninskiye Gory, 1, Building 12 
Moscow 119234, Russia 
3 Shenzhen MSU-BIT University 
1 International University Park Road 
Dayun New Town 
Longgang District 
Shenzhen 518172, China 
The soles of the genus Typhlachirus 
(family Soleidae) are found in marine 
and brackish water and distinguished 
by the absence of eyes. Three nominal 
species of the genus—T. lipophthalmus 
(Karoli, 1882), T: caecus Hardenberg, 
1931, and the Mekong blind sole (T. elon- 
gatus) Pellegrin and Chevey, 1940— 
have been described from the Indo-West 
Pacific. Currently, they are all considered 
valid (Fricke et al., 2021). Until recently, 
blind sole were poorly represented 
in ichthyological collections: a total 
of 15 individuals have been reported 
(Karoli, 1882; Hardenberg, 1931a, 1931b; 
Pellegrin and Chevey, 1940; Atack, 2006; 
Evseenko and Bolshakov, 2018; Tan 
and Grinang, 2020). Of these individ- 
uals, 5 specimens of T: lipophthalmus 
were caught from the coastal waters off 
the northwestern coast of Kalimantan, 
the Indonesian territory on the island 
of Borneo (Karoli, 1882; Atack, 2006; 
4 Vavilov Institute of General Genetics 
Russian Academy of Sciences 
Gubkina Street, 3 
Moscow 119333, Russia 
> Kovalevsky Institute of Biology of the 
Southern Seas 
Russian Academy of Sciences 
Nakhimov Prospekt, 2 
Sevastopol 299011, Russia 
© Severtsov Institute of Ecology and Evolution 
Russian Academy of Sciences 
Leninskiy Prospekt, 33 
Moscow 119071, Russia 
Tan and Grinang, 2020), 5 specimens of 
T. caecus were caught from the mouth 
of the Rokan River in the Strait of 
Malacca between Sumatra Island of 
Indonesia and the Malay Peninsula 
(Hardenberg, 1931a, 1931b), and 5 spec- 
imens of T: elongatus were caught from 
the estuarine part of the Mekong River 
in Vietnam (Pellegrin and Chevey, 1940; 
Evseenko and Bolshakov, 2018). How- 
ever, Abidin and Bintoro (2014) reported 
about 491 blind sole from the estuarine 
part of the Indragiri River of Sumatra 
Island. This circumstance indicates that 
these species are relatively abundant 
and are frequently caught as bycatch in 
local fisheries. 
The 3 species of blind sole are very 
similar in external morphology, meristic 
features, and body proportions; therefore, 
distinguishing between them is diffi- 
cult. The features that the authors of 
the first descriptions note as diagnostic 
