Lateral line system of flatfishes (Pleuronectiformes): Diversity and taxonomic distribution of its characters

Abstract

An analysis of lateral line system (LLS) morphology in 304 species (39% of those presently known) from 121 (92%) genera belonging to all 14 families of Pleuronectiformes is presented. The main feature of the LLS of flatfishes is bilateral asymmetry in the course of the cranial lateral line canals, but also in the reduction of canals or portions of canals, which occurs independently on the eyed and blind sides. The number of reductions is used to define two patterns for comparative analysis. A complete pattern is defined by the presence of all main canals, connected with each other, and the canaliculi that end in pores are usually highly branched. The reduced pattern is defined by the presence of more than two reductions. Each family is characterized by the occurrence of a complete pattern, a reduced pattern or both patterns. The combination of reductions varies considerably and characterizes taxa at the generic level. A reduced pattern appears independently several times and has a complex evolutionary history with reversals to a complete pattern. This study has shown that LLS characters are very informative for phylogeny and taxonomy and should be an important component of the description and revision of pleuronectiform taxa and their relationships.

Full text

Acta Zoologica. 2019;00:1–25. wileyonlinelibrary.com/journal/azo
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© 2019 The Royal Swedish Academy of Sciences
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INTRODUCTION
Investigation of the lateral line system (LLS) has a long
history, and some generalizations about its diversity in tele-
osts have already been made (Bird & Webb, 2014; Coombs,
Janssen, & Webb, 1988; Makushok, 1961; Mandritsa, 2001;
Neyelov, 1979; Sideleva, 1982; Webb, 2014). Several trends
in the LLS such as evolution of widened, branched and re-
duced canals have been described in different groups of
bony fishes (Webb, 2014). The characters of the LLS have
been used successfully in the taxonomy of teleosts. A few
major taxa can be defined by the characteristics of the LLS.
The LLS provides a valuable context for novel analyses of
the relationship between developmental processes and the
evolution of behaviourally and ecologically relevant pheno-
types in fishes. The evolution of a reduced LLS is believed to
be related to the depth and flow environment, although this
relationship is still a bit ambiguous (Mandritsa, 2001; Nakae,
Shinohara, Miki, Abe, & Sasaki, 2013).
The comparative study of the LLS in the Pleuronectiformes
is of special interest. Flatfishes are bilaterally asymmetrical,
and as a result, they share unique morphological specializa-
tions of various external and internal structures. It is of in-
terest to evolutionary biologists, ichthyologists and fisheries
ecologists to know how their great diversity in morphology,
biology and specialized adaptations translates into the evo-
lutionary and ecological success of these fishes. The LLS
of the head in flatfishes was described for the first time in
Received: 29 December 2018
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Revised: 2 September 2019
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Accepted: 3 September 2019
DOI: 10.1111/azo.12311
ORIGINAL ARTICLE
Lateral line system of flatfishes (Pleuronectiformes): Diversity
and taxonomic distribution of its characters
Elena P.Voronina1
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Valentina G.Sideleva1
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Dianne R.Hughes2
1Laboratory of Ichthyology,Zoological
Institute,Russian Academy of Sciences, St.
Petersburg, Russia
2Australian Centre for Microscopy and
Microanalysis (ACMM),Madsen Building
F09,The University of Sydney, Sydney,
NSW, Australia
Correspondence
Elena P. Voronina, Laboratory of
Ichthyology, Zoological Institute, Russian
Academy of Sciences, Universitetskaya
emb., 1, St. Petersburg 199034, Russia.
Email: voron@zin.ru
Funding information
State Assignment, Grant/Award Number:
АААА‐А17‐117030310197‐7
Abstract
An analysis of lateral line system (LLS) morphology in 304 species (39% of
those presently known) from 121 (92%) genera belonging to all 14 families of
Pleuronectiformes is presented. The main feature of the LLS of flatfishes is bilateral
asymmetry in the course of the cranial lateral line canals, but also in the reduction of
canals or portions of canals, which occurs independently on the eyed and blind sides.
The number of reductions is used to define two patterns for comparative analysis.
A complete pattern is defined by the presence of all main canals, connected with
each other, and the canaliculi that end in pores are usually highly branched. The
reduced pattern is defined by the presence of more than two reductions. Each family
is characterized by the occurrence of a complete pattern, a reduced pattern or both
patterns. The combination of reductions varies considerably and characterizes taxa
at the generic level. A reduced pattern appears independently several times and has
a complex evolutionary history with reversals to a complete pattern. This study has
shown that LLS characters are very informative for phylogeny and taxonomy and
should be an important component of the description and revision of pleuronectiform
taxa and their relationships.
KEYWORDS
flatfishes, lateral line canals, morphology, Pleuronectiformes, taxonomy

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VORONINA et Al.
Scophthalmus maximus (Scophthalmidae), Hippoglossus hip-
poglossus and Pleuronectes platessa (Pleuronectidae) (Cole
& Johnstone, 1902; Traquair, 1865). Some LLS characters
are given in descriptions of external morphology and in oste-
ological studies of flatfishes (Amaoka, 1969; Appelbaum &
Schemmel, 1983; Bürgin, 1986; Cervigón, 1985; Chapleau,
1993; Cooper & Chapleau, 1998; Hensley & Ahlstrom,
1984; Hoshino, 2001, 2006; Matsubara & Ochiai, 1963;
Ochiai, 1963; Ramos, 2003; Sakamoto, 1984). The LLS of
the head has been studied in detail in Engyprosopon gran-
disquama (Bothidae) and Pseudorhombus pentophthalmus
(Paralichthyidae) (Sasaki, Takiuye, & Nakae, 2007) and in
Pardachirus pavoninus (Soleidae) (Sato, Nakamoto, Nakae,
& Sasaki, 2018). Differences in the form of the canals, num-
ber of pores and the degree of branching of the canaliculi have
been used in the diagnosis of citharid, pleuronectid and soleid
taxa (Hoshino, 2000, 2001; Hubbs, 1945; Orr & Matarese,
2000; Randall, 2007; Randall & Desoutter‐Meniger, 2007;
Vachon, Chapleau, & Desoutter‐Meniger, 2008). Comparison
of the LLS among the six flatfish families showed diversity
of characters that define different genera (Voronina, 2009,
2010).
The current study provides a comparative account of the
LLS of the head, the taxonomic distribution of LLS charac-
ters and their use in distinguishing among flatfish taxa.
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MATERIALS AND METHODS
The current study uses specimens studied for the first time or
data published earlier by the first author. The LLS in a total
of 39% species belonging to 92% of the genera of flatfishes
is compared (Table 1). Specimens of the 197 species in 81
genera examined for the first time in the current study are
listed in the Appendix 1. The taxonomy used is in accord-
ance with recent classifications (Fricke, Eschmeyer, & Laan,
2018; Vinnikov, Thomson, & Munroe, 2018).
Cranial lateral line canals were examined with methylene
blue injection following the method of Ueno (1970) (Figure
1a,c) and described following the terminology of Webb
(1989). Cleared and stained preparations were also examined
to supplement injected specimens (Figure 2a).
Drawings made from photographs are oriented with ros-
tral to the top and show the LLS on the eyed and blind sides
of the head in both right‐eyed and left‐eyed flatfishes, if not
otherwise indicated. The coronal commissure is shown as a
dashed line, since it is much shorter in reality than it appears.
Jaws and preopercular margins are shown, usually in the first
diagram of each of the figures.
In order to illustrate LLS evolution, we used the most recent
molecular phylogeny of the pleuronectiformes (Betancur‐R
& Ortí, 2014) and expanded the pleuronectid branch with a
simplified version of its phylogeny (Vinnikov et al., 2018).
In this tree, the suprageneric taxa and only some pertinent
genera are included. The ancestral state within the order was
reconstructed in Mesquite 3.6. It revealed nine steps tracing
the character history in the most parsimonious phylogeny.
Institutional acronyms are as listed by Sabaj (2019).
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RESULTS
3.1
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Topography of the lateral line canals of
the head in the pleuronectiformes
The general association of the lateral line canals with particu-
lar skull bones in all pleuronectiform species is the same as in
other groups of bony fishes. In the most fully developed LLS,
all main canals of both sides of the head are present and con-
nect with each other (Figure 3). Primary canaliculi branch off
the main canals and may be highly branched (Figure 1a,b).
Frequent modifications are the absence of canals or por-
tions of canals and the presence of unbranched, instead of
branched, canaliculi (Figure 1c,d).
The supraorbital canal (SOC) passes through nasal and
frontal bones (Figures 3, 4). The eyed side SOC is reduced
TABLE 1 Summary of flatfishes analysed in this study in
comparison to number of their known taxa
Family
Genera Species
Known Studied Known Studied
Psettodidae 1 1 3 3
Citharidae 4 4 6 5
Scophthalmidae 4 4 8 8
Paralichthyidae 14 14 112 46
Pleuronectidae
Atheresthinae 1 1 2 2
Pleuronichthyinae 1 1 8 4
Microstominae 2 2 9 8
Hippoglossinae 6 6 9 9
Pleuronectinae 14 14 31 31
Bothidae 20 20 162 68
Paralichthodidae 1 1 1 1
Poecilopsettidae 3 3 21 15
Rhombosoleidae 9 8 19 12
Achiropsettidae 4 4 4 4
Samaridae 4 4 27 12
Achiridae 9 7 35 19
Soleidae 32 24 174 50
Cynoglossidae
Symphurinae 1 1 75 1
Cynoglossinae 2 2 68 6
Total 132 121 774 304

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VORONINA et Al.
in 9 of 121 or 7% of the genera studied (Figure 5 and Table
2). The portion of the eyed side SOC is absent in the nasal
bone in nine genera, and the interorbital part of the SOC is
also absent in the frontal bone in eight genera. The blind side
SOC is reduced in 48 (or 40%) of the genera examined and
the interorbital portion of the canal is absent in 31 genera.
The different degree of the development of the interorbital
part of the frontal bone of the blind side has been described
earlier in flatfish taxa (Amaoka, 1969; Chabanaud, 1934;
Sakamoto, 1984). The interorbital portion of the blind side
SOC is predictably absent in genera when the interorbital part
of the frontal bone is absent. In the genera with developed
interorbital part of the bone, according to our data, a canal is
usually present, but it is absent in several genera.
The infraorbital canal (IOC) passes through the lacrimal
and infraorbital bones. The portion of the eyed side IOC in
the lacrimal is not usually connected with the other canals.
The number of infraorbital bones containing the IOC varies
from 1 to 31 on the eyed side, and from 6 to 10 on the blind
side among species. The eyed side IOC is reduced in 111 (or
92%) of the genera studied, and among them, this canal is
totally absent in 46 genera, the portion of the eyed side IOC
in the lacrimal is absent in 28 genera and the portion in the
infraorbitals is absent in 37 genera. On the blind side, the
IOC is absent in 52 (or 43%) of the genera.
The otic canal (OTC) passes through the pterotic bone.
The OTCs of the eyed and blind sides are symmetrical, and
their reduction is very rare among flatfishes.
The postotic canal (POC) passes through the supratempo-
ral and posttemporal bones, and in several genera, it passes
also through the supracleithrum. The POCs of the eyed and
blind sides are symmetrical, and their reduction is very rare.
The POC meets the trunk canal, which is present usually on
both sides of the body, or on the eyed side only or it may be
absent.
The mandibular canal (MDC) passes through the dentary
and the anguloarticular bones. This canal is partly or totally
absent on one or both sides of the head—on the eyed side it
FIGURE 1 Lateral line canals of the flatfish head. (a, b)
Complete pattern with highly branched canaliculi in Tephrinectes
sinensis. (c, d) Reduced pattern with unbranched canaliculi and
absence of infraorbital canal of the eyed side and interorbital portion of
the supraorbital canal of the blind side in Citharichthys dinoceros. (a,
c) Canals injected with methylene blue. (b, d) Diagrams drawn from
photographs. Arrow shows interruption between canals, dashed line—
coronal commissure. Scale bar 1cm
FIGURE 2 Reduced pattern of the lateral line canals of the
head in Cynoglossus quadrilineatus. (a) Dermal canals in the scales
cleared and alizarin stained. (b) Diagram drawn from photograph. f′
and f″, frontal of eyed and blind side, respectively; pop′ and pop″,
preoperculum of eyed and blind side, respectively, solid lines—dermal
canals. Scale bar 1cm

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VORONINA et Al.
is absent in 44 genera and on the blind side it is absent in 49
genera (36% and 41% of the genera, respectively).
The preopercular canal (PRC) passes through the pre-
operculum. This canal is partly or totally reduced on the eyed
side in four genera and on the blind side in five genera.
Three canals (SOC, IOC and OC) meet within the frontal
bones of the eyed and the blind side. The coronal commissure
(COC) passes through the frontals and connects the canals of
both sides of the head (Figure 6). A single canaliculus branches
off the COC usually between the two frontal bones (Figure 6a,b),
but less often on the frontal of the blind side (Figure 6d,f), or
the canaliculus is absent (Figure 6m). This canaliculus may be
unbranched (Figure 7a,b), highly branched (Figure 7d,e,f,h) or
may occur as a long branch along dorsal margin of the upper eye
(Figure 7c,g). In two genera, the COC is interrupted, and there
are two canaliculi in close proximity but they arenot connected
to each other (Figure 6i). The COC is absent in five genera.
The supratemporal canal (STC) passes through the supra-
temporal and extrascapular bones. We consider the STC as
reduced, if it is shorter and goes through a reduced number
of extrascapulars, compared to related taxa or to other side of
the head. A reduced STC on the eyed and blind sides occurs
in 19 and 27 genera, respectively.
The canaliculi are unbranched in 66 genera where each
canaliculus ends in a single primary pore. The canaliculi are
highly branched and end in numerous secondary pores in
65 other genera (Figure 1a,b). The number of pores in spe-
cies with highly branched canaliculi can be in the hundreds
(Figure 7h). The morphology of the canaliculi on the eyed
and blind sides is similar, although in some species with
branched canaliculi the degree of the branching is somewhat
less extensive on the blind side than the eyed side. The can-
aliculi can be absent, and in such cases, only primary pores
occur as perforations in the main canals. The number and lo-
cation of primary canaliculi corresponding to the number of
primary pores is of taxonomic importance.
Interruptions often occur in different canals, most com-
monly in the eyed side IOC such that the portion of the IOC
in the lacrimal is not connected to the other canals in the ma-
jority of species (Figure 4e,f). The interruption between the
MDC and the PRC on one or both sides of the head is found
in a number of species (Evseenko, 2000; Voronina, 2009).
The interruption in the COC and between the PRC and the
POC on the blind side is found in few genera. Widened canals
on the blind side, a dorsal branch of the STC, small solitary
canal segments with ossified walls, and a connection be-
tween the COC and STC are additional characteristics found
in some genera. A special feature of the canals is found in the
cynoglossids, some soleids and the achirids. In these taxa,
the canals or portions of canals are not associated with bones,
but with the skin or scales only, and so are designated here
as dermal canals or dermal portions of canals. In achirids and
soleids, the dermal canals are in the same location as the ca-
nals in other flatfishes (e.g. POC is in the skin over the pre-
operculum), but in the cynoglossids the course of the dermal
canals differs considerably from that of the canals typical for
other flatfishes (Figure 2a,b).
3.2
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Taxonomic distribution of
LL characters
The lateral line canals of the head were compared within
and among the 14 families of flatfishes. For this compara-
tive analysis of LLS diversity, two canal patterns are defined
based on the presence and number of reductions (i.e. the ab-
sence of the canals or portions of the canals, interruptions
between canals or portions of the canals and the presence of
unbranched canaliculi). In a complete pattern, all the main
canals are present and connected to each other and the cana-
liculi are usually highly branched. One or two canal reduc-
tions occur in some genera with a complete pattern as an
exception. A reduced pattern is defined by the presence of
more than two reductions. In the current paper, the terms
“complete” and “reduced” patterns are used to describe and
compare the complex of all the main canals and canaliculi on
the head. Each family is characterized by the occurrence of a
FIGURE 3 General scheme of the lateral line canals and
primary canaliculi of flatfishes. Bone abbreviations (red in figure):
aa, anguloarticular; de, dental; exs, extrascapular; f, frontal of ocular
and blind sides; inf, infraorbital; la, lacrimal; na, nasal of ocular
and blind sides; pop, preopercular; pt, pterotic; ptt, posttemporal;
st, supratemporal bone. Canal abbreviations (blue in figure): COC,
coronal commissure; IOC, infraorbital; MDC, mandibular; OTC,
otic; pc, primary canaliculi; POC, postotic; PRC, preopercular; SOC,
supraorbital; STC, supratemporal canal

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VORONINA et Al.
complete and/or a reduced pattern. The combination of canal
reductions varies considerably and characterizes taxa at the
generic level. Finally, variations, if they take place among
species within one genus, are pointed out.
3.2.1
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Family Psettodidae
A complete LLS pattern is found in all three species of
the single genus Psettodes (Voronina, 2007; our data;
Figure 8). Characteristics of the genus: the blind side IOC
goes through the fused infraorbital and frontal bones; the
OTC goes through the sphenotic bone and the POC goes
through the supracleithrum (Figures 4a, 6a). The eyed side
IOC in the lacrimal connects with the portion of this canal
in the infraorbitals (from now on we mean the portion of
the canal in the relevant bone). Three primary canaliculi
branch off the MDC through the openings in the anguloar-
ticular bone on both sides of the head whereas only two
FIGURE 4 Association of the
eyed side lateral line canals with skull
bones of flatfishes. (a) Psettodes erumei.
(b) Lepidorhombus whiffiagonis. (c)
Atheresthes evermanni. (d) Pleuronectes
platessa. (e) Cleisthenes herzensteini. (f)
Oncopterus darwinii. aa, anguloarticular;
de, dental; exs, extrascapular; f, frontal;
inf, infraorbital; la, lacrimal; lls, lateral
line scale; na, nasal; pa, parietal; pop,
preopercular; pt, pterotic; ptt, posttemporal;
sph, sphenoticum; st, supratemporal; su,
supracleitrum. IOC, infraorbital; MDC,
mandibular; OTC, otic; POC, postotic;
PRC, preopercular; SOC, supraorbital; STC,
supratemporal canal. Drawings for right‐
eyed species (c–f) are reversed for better
comparison. Note highly branched canaliculi
(c) and unbranched canaliculi (d)

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VORONINA et Al.
primary canaliculi branch off the MDC between the angu-
loarticular and the neighbouring dentary and preoperculum
in all other species studied.
3.2.2
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Family Citharidae
Both complete and reduced patterns are found among spe-
cies in this family (Figure 9). A complete pattern is found in
Citharus and Citharoides (Figure 9a,b) and a reduced pattern
is found in Brachypleura and Lepidoblepharon (Figure 9c,d).
The canal reductions are shown in Table 3. Characteristics of
genera: in Citharus and Citharoides, the POC goes through
the supracleithrum; in Brachypleura, the SOC in the nasal and
IOC in the lacrimal and the infraorbitals are absent on both
the eyed and blind sides of the head; in Lepidoblepharon,
the interorbital portion of the SOC in the frontal bone on the
blind side and the IOC in the infraorbitals on the eyed side are
absent, the STC is reduced on both sides, the canaliculi are
unbranched and the POC goes through the supracleithrum.
3.2.3
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Tephrinectes
A complete LLS pattern is present in this monotypic genus which
is of unclear taxonomic position (Figure 1a,b). Characteristic
of genus: the POC passes through the supracleithrum.
3.2.4
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Family Scophthalmidae
Both complete and reduced patterns occur among species in
this family (Voronina, 2010; Figure 10). A complete pattern
is present in Scophthalmus, Lophopsetta and Lepidorhombus
and a reduced pattern is found in Zeugopterus and
Phrynorhombus. The reductions found among genera in this
family are shown in the Table 4. Characteristics of genera:
in Scophthalmus, the eyed side IOC in the lacrimal is con-
nected with other canals (Figure 10a); in Lophopsetta, the
eyed side IOC in the infraorbitals is absent (Figure 10b);
in Lepidorhombus, the eyed side IOC is absent in both the
infraorbitals and lacrimal (Figure 10c); in Zeugopterus, the
eyed side IOC is absent in the infraorbitals and lacrimal, the
STC is reduced so that only one to four pores are present,
canaliculi are unbranched (Figure 10d); in Phrynorhombus,
the eyed side IOC is absent in the infraorbitals and lacrimal,
the eyed side MDC is reduced so that only two pores are pre-
sent, the STC is reduced so that only one or two pores are pre-
sent, and unbranched canaliculi and an interruption between
the MDC and PRC are present (Figure 10e). Variation within
genus: an interruption between the MDC and PRC is present
on the eyed side of Zeugopterus regius and the interruption is
absent in Z.punctatus.
3.2.5
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Family Paralichthyidae
Both complete and reduced LLS patterns are found among
the species studied (Voronina & Diaz de Astarloa, 2012;
our data; Figure 11). A complete pattern is found in
13 genera (Ancylopsetta, Cephalopsetta, Gastropsetta,
Hippoglossina, Lioglossina, Paralichthys, Pseudorhombus,
Tarphops, Xystreurys, Cyclopsetta, Citharichthys, Etropus
and Syacium; Figure 11a–e), and a reduced pattern is only
found in one genus (Thysanopsetta) with total absence of
the eyed side IOC, a reduced STC, unbranched canaliculi,
an interruption between the PRC and the POC on blind
side, and an interruption between the MDC and the PRC
on both sides (Figure 11f). Characteristics of genera: in
Hippoglossina, the interorbital portion of the blind side
SOC is absent (Figure 11b); in Cyclopsetta, Citharichthys,
Etropus and Syacium, the eyed side IOC in the infraorbitals
FIGURE 5 Summarized frequency of the reductions in the
lateral line canals of the head in flatfishes. Reduction of canal is
found in 92% (black), 21%–43% (grey) and 3%–7% (white) of the
121 genera studied. Canal abbreviations: COC, coronal commissure;
IOC, infraorbital; MDC, mandibular; OTC, otic; POC, postotic; PRC,
preopercular; SOC, supraorbital; STC, supratemporal canal
TABLE 2 Occurrence of reductions of the lateral line system of
the head in 121 flatfish genera studied
Canal
Number of genera with reduction
(% of the total number of studied
genera)
Eyed side Blind side
Supraorbital 9 (7%) 48 (40%)
Infraorbital 111 (92%) 52 (43%)
Otic, postotic 7 (6%) 8 (7%)
Preopercular 4 (3%) 5 (4%)
Mandibular 44 (36%) 49 (41%)
Supratemporal 25 (21%) 27 (22%)

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VORONINA et Al.
and interorbital portion of the blind side SOC are absent
(Figure 11c–e). Variation within genus: in nine Paralichthys
species studied canaliculi branching varies, the eyed side
IOC in the lacrimal is absent in P.orbignyanus, P.oblon-
gus, P. isosceles, P. adspersus; in Citharichthys species,
the blind side STC is reduced so that only one to two pores
are present and canaliculi are unbranched in C.dinoceros
(Figures 1c,d, 11d,e); in Hippoglossina species, an inter-
ruption between the MDC and the PRC is present on the
eyed side of H. macrops, but there is no interruption in
H.bollmani.
3.2.6
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Family Bothidae
Only a reduced LLS pattern is found (Figure 12). The inter-
orbital part of the blind side SOC and the eyed side IOC in
the infraorbitals are absent, the STC is reduced on the blind
side or on both the eyed and blind sides and unbranched
canaliculi (except Bothus) are present. Characteristics of
genera: in Bothus, the canaliculi are branched (Figure 12a);
in four genera (Crossorhombus, Trichopsetta, Parabothus
and Grammatobothus), only the canaliculus of the COC
is branched (Figure 12b); in four genera (Taeniopsetta,
FIGURE 6 Dorsal view of frontal
bones of flatfishes. (a) Psettodes erumei. (b)
Scophthalmus maximus. (c) Paralichthys
olivaceus. (d) Hippoglossina macrops. (e)
Arnoglossus kessleri. (f) Bothus myriaster.
(g) Pleuronichthys cornutus. (h) Liopsetta
glacialis. (i) Pseudopleuronectes obscurus.
(j) Azigopus pinnifasciatus. (k) Mancopsetta
maculata. (l) Microchirus variegatus.
(m) Cynoglossus quadrilineatus. IOC,
infraorbital, SOC, supraorbital and OTC,
otic canals of eyed (o) and blind (b) side,
respectively; COC, coronal commissure;
f and f′, frontal bone of eyed and blind
side, respectively; f′+inf, fused frontal and
infraorbital bones; ip and ip′—interorbital
processus of frontal bone of eyed and blind
side, respectively. Arrow shows the origin
of canaliculus of coronal commissure.
Drawings for right‐eyed species (g, h, i, j, l)
are reversed for better comparison

8
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VORONINA et Al.
Monolene, Perissias and Chascanopsetta), an interruption
between the MDC and the PRC is present (Figure 12d).
Variation within genus: among Bothus species studied can-
aliculi are unbranched only in B. ocellatus; an interruption
between the MDC and the PRC is found on the eyed side
in three of eight Arnoglossus species (A. septemventralis,
A.macrolophus and A.aspilos) and on both sides in A.kes-
sleri; in Parabothus and Arnoglossus species, the number of
pores in the canaliculus of the COC varies from one to four
(Figure 7b,c).
3.2.7
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Family Pleuronectidae
Both complete and reduced patterns occur among species
studied (Voronina, 2002, 2003, 2005; Figures 13, 14). The
reductions are shown in the Table 5.
A complete pattern is found in eight genera.
Characteristics of these genera: in Atheresthes and Verasper,
the eyed side IOC in the lacrimal is absent (Figures 4c,
13a,c); in Pleuronichthys, the eyed side IOC in the lacrimal
is absent and additional branches of the STC and the PRC are
present (Figure 13b); in Hippoglossus, the eyed side IOC in
the lacrimal is absent and the anterior portion of the STC is
connected with the COC (Figure 13d); in Reinhardtius, the
canaliculi are unbranched and the anterior portion of the STC
is connected to the COC (Figure 13e); in Clidoderma, the
canaliculi are unbranched and an interruption between the
MDC and the PRC is present (Figure 13f); in Eopsetta, the
interorbital portion of the blind side SOC and the eyed side
IOC in the lacrimal is absent (Figure 13g); in Acanthopsetta,
the interorbital portion of the blind side SOC is absent, cana-
liculi are unbranched and three (vs. two typical for flatfishes)
primary pores are present in the eyed side SOC.
A reduced pattern defined by the absence of the eyed
side IOC in the lacrimal (except Cleisthenes) and the in-
terorbital portion of the blind side SOC, by the presence
of unbranched canaliculi, is found in 16 other pleuronec-
tid genera (Figure 14a). Characteristics of these genera: in
Cleisthenes, the blind side SOC in the nasal is absent, the
eyed side IOC in the lacrimal and three to four primary
pores in the eyed side SOC are present (Figure 14b); in
FIGURE 7 Canaliculus of the
coronal commissure in flatfishes. (a)
Pleuronectes quadrituberculatus. (b)
Arnoglossus imperialis. (c) Arnoglossus
sayaensis. (d) Glyptocephalus kitaharae. (e)
Hippoglossina macrops. (f) Pleuronichthys
cornutus. (g) Achirus achirus. (h)
Hippoglossus hippoglossus. (a) Total view
of the head with overlapping drawing of
the supraorbital (SOC), infrarbital (IOC)
and otic (OTC) canals of eyed side, coronal
commissure (COC) and canaliculus of the
coronal commissure (arrow). (b–h), only
canaliculus of the coronal commissure.
Rostral to the left, drawings for right‐eyed
species (a, d, f, g, h) are reversed for better
comparison
FIGURE 8 Psettodidae. Complete pattern of the lateral line
canals of the head in Psettodes erumei

|
9
VORONINA et Al.
Hippoglossoides, the blind side SOC in the nasal is absent
and an interruption in the COC is present (Figure 14c); in
Lyopsetta, an interruption between the MDC and the PRC
is present (Figure 14d); in Glyptocephalus, the canals of
the blind side are considerably widened (Figure 14e); in
Isopsetta, Lepidopsetta, Parophrys and Psettichthys, dor-
sal branches of the STC and a long‐branched canaliculus
of the COC are present (Figure 14g); in Liopsetta, the
eyed side IOC is reduced so that there are only one to
three pores present (Figure 14h); in Myzopsetta, the blind
side SOC in the nasal is absent and the STC is reduced; in
Pseudopleuronectes, the blind side SOC in the nasal is ab-
sent and there is interruption in the COC; in Microstomus,
the MDC is reduced so that there are only four primary
FIGURE 9 Citharidae. Complete
pattern of the lateral line canals of the
head in the left‐eyed species (a, b) and
reduced pattern in the right‐eyed species
(c, d). (a) Citharoides macrolepis (b)
Citharus linguatula. (c) Brachypleura
novaezeelandiae. (d) Lepidoblepharon
ophthalmolepis
FIGURE 10 Scophthalmidae.
Complete (a–c) and reduced (d, e) pattern
of the lateral line canals of the head. (a)
Scophthalmus rhombus. (b) Lophopsetta
aquosa. (c) Lepidorhombus whiffiagonis. (d)
Zeugopterus punctatus. (e) Phrynorhombus
norvegicus. Arrow shows interruption
between mandibular and preopercular canals

10
|
VORONINA et Al.
pores on both sides (Figure 14i); in Dexistes, the blind side
SOC in the nasal is absent. Variation within genus: num-
ber of primary pores in the MDC, PRC and COC varies
within Lepidopsetta species; the canals are not widened on
the blind side of G. kitaharae (Figure 14f), distinguishing
this species from other Glyptocephalus species; absence of
the blind side SOC in the nasal, reduced STC on both sides
of the head and eyed side IOC distinguish M. bathybius
(Figure 14j) from other Microstomus species.
3.2.8
|
Family Paralichthodidae
A complete LLS pattern is present in the single species of
Paralichthodes in this monotypic family (Figure 15).
FIGURE 11 Paralichthyidae.
Complete (a–e) and reduced (f) pattern
of the lateral line canals of the head. (a)
Pseudorhombus arsius. (b) Hippoglossina
macrops. (c) Syacium papillosum. (d)
Citharichthys arctifrons. (e) Citharichthys
dinoceros. (f) Thysanopsetta naresi
FIGURE 12 Bothidae. Reduced
pattern of the lateral line canals of the
head. (a) Bothus podas. (b) Crossorhombus
azureus. (c) Asterorhombus intermedius. (d)
Monolene helenensis

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11
VORONINA et Al.
3.2.9
|
Family Poecilopsettidae
A reduced LLS pattern is found in the species studied (Figure
16). It is defined by the absence of the IOC on both sides, the
reduction of the MDC so that there are only two pores and
the reduction of the STC so that there are only one to three
pores, an interruption between the MDC and the PRC, and
unbranched canaliculi (Voronina, 2009). Characteristics of
genera: in Marleyella and Poecilopsetta, the eyed side SOC
in the nasal is absent (Figure 16a); in Nematops, an interrup-
tion between the POC and PRC is present on the blind side
(Figure 16b).
3.2.10
|
Family Rhombosoleidae
Both complete and reduced LLS patterns are found in
species studied (Voronina, 2009; Voronina & Diaz de
Astarloa, 2007; our data; Figure 17). A complete pattern is
found in Oncopterus. A reduced pattern with unbranched
canaliculi (except Psammodiscus) and a different set of
canal reductions is found among the seven genera (Table
6). Characteristics of genera: in Oncopterus, the STC
goes through the parietal, a very long canaliculus of the
COC with an ossified wall, additional branches of the
STC and solitary canal segments are present (Figures 4f,
17a); Pelotretis lacks the eyed side IOC in the infraor-
bitals, an interruption between the MDC and the PRC is
present (Figure 17b); Psammodiscus lacks the blind side
SOC and the COC, its canaliculi are branched (Figure
17c); Colistium lacks the SOC in the nasals of both sides
and the interorbital portion of the blind side SOC, soli-
tary canal segments are present (Figure 17d); Ammotretis
lacks the interorbital portion of the blind side SOC, the
eyed side IOC in the infraorbitals and the COC (Figure
17e); Rhombosolea lacks the interorbital portion of the
blind side SOC, the eyed side IOC in the infraorbitals and
the COC, an interruption between the MDC and the PRC
is present (Figure 17f); Azygopus lacks the interorbital
portion of the blind side SOC, the eyed side IOC in the
infraorbitals, its MDC and STC are reduced so that there
are only two to four pores in these canals, an interruption
between the MDC and the PRC is present (Figure 17g);
FIGURE 13 Pleuronectidae.
Complete pattern of the lateral line canals
of the head. (a) Atheresthes evermanni.
(b) Pleuronichthys cornutus. (c) Verasper
variegatus. (d) Hippoglossus hippoglossus.
(e) Reinhardtius hippoglossoides. (f)
Clidoderma asperrimum. (g) Eopsetta
grigorjewi. Arrow shows connection of
anterior part of the supratemporal canal with
the coronal commissure; ab—additional
branch of the canal

12
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VORONINA et Al.
Peltorhamphus lacks the COC, the interorbital portion of
the blind side SOC and the eyed side IOC in the infraor-
bitals, the MDC and STC are reduced so that there are
only two to four pores in these canals, an interruption be-
tween the MDC and the PRC is present, canals are wider
and pores larger on the blind side than on the eyed side
(Figure 17h).
3.2.11
|
Family Achiropsettidae
A reduced LLS pattern is found in all species and is defined
by the absence of the portion of the eyed side IOC in the
infraorbitals and the entire blind side IOC, a reduced STC so
that there are only one to three pores, an interruption between
the MDC and the PRC, and by unbranched canaliculi (Figure
FIGURE 14 Pleuronectidae
(continued). Reduced pattern of the lateral
line canals of the head. (a) Platichthys
flesus. (b) Cleisthenes herzensteini. (c)
Hippoglossoides platessoides. (d) Lyopsetta
exilis. (e) Glyptocephalus zachirus. (f)
G. kitaharae,. (g) Parophrys vetulus. (h)
Liopsetta glacialis. (i) Microstomus kitt.
(j) Microstomus bathybius. Arrow shows
interruption in the coronal commissure;
ab—additional branch of the canal. Note
the widened canals of the blind side in G.
zachirus (e) and not widened in G. kitaharae
(f)

|
13
VORONINA et Al.
18a). Characteristics of genera: in Pseudomancopsetta, the
blind side OTC is absent (Figure 18b).
3.2.12
|
Family Samaridae
A reduced LLS pattern is found in all species studied and is de-
fined by the total absence of the IOC, the reduction of the MDC
with only two pores, and the reduction of the STC with only one
to three pores on both sides, and by unbranched canaliculi (Figure
19a; Voronina, 2009; Voronina & Suzumoto, 2017). An inter-
ruption between the MDC and the PRC is present on both sides.
Characteristics of genera: in Samaris and Plagiopsetta, the blind
side SOC is absent in the interorbital part of frontal and in the nasal
(Figure 19b); in Samaretta, the blind side SOC, the OTC and POC
FIGURE 15 Paralichthodidae. Complete pattern of the lateral
line canals of the head in Paralichthodes algoensis
FIGURE 16 Poecilopsettidae.
Reduced pattern of the lateral line canals
of the head. (a) Poecilopsetta normani.
(b) Nematops macrochirus. Arrows show
interruptions between the mandibular,
preopercular and the postotic canals
FIGURE 17 Rhombosoleidae.
Complete (a) and reduced (b, c, d, e, f, g)
pattern of the lateral line canals of the head.
(a) Oncopterus darwinii. (b) Pelotretis
flavilatus. (c) Psammodiscus ocellatus.
(d) Colistium nudipinnis. (e) Ammotretis
rostratus. (f) Rhombosolea tapirina. (g)
Azygopus pinnifasciatus. (h) Peltorhamphus
novaezeelandiae. Arrow shows solitary
canal segments; ab—additional branch of
the canal

14
|
VORONINA et Al.
are absent on both sides, and the PRC is reduced so that there are
only four or five primary pores (Figure 19c).
3.2.13
|
Family Achiridae
All species studied have a reduced pattern characterized by
the absence of the eyed side IOC in the lacrimal, absence
of the blind side IOC and the MDC and the presence of a
long ossified branch of the canaliculus of the COC (Figure
20a,b). Characteristics of genera: in Apionichthys, the eyed
side IOC in the infraorbitals and the blind side SOC are
absent (Figure 20c); in Gymnachirus, canaliculi are un-
branched, the interorbital portion of the SOC of both sides
and the blind side SOC in the nasal are absent, and the OTC
and PRC are dermal canals that are not associated with the
skull bones and pass through the skin over the pterotic and
preoperculum, respectively (Figure 20d). Variation within
genus: in Trinectes species, the blind side STC varies from
long to very short and the eyed side IOC is absent in three
species (T.fluviatilus, T.microphthalmus, T.xanthurus).
3.2.14
|
Family Soleidae
A reduced LLS pattern is found in all species studied
(Figure 21). It is defined by the absence of the IOC on both
sides, the reduction of the MDC so that only two primary
canaliculi are present on the eyed side, and the absence of
the MDC on the blind side (Figure 21a). Characteristics of
genera: in eight genera (Aesopia, Bathysolea, Brachirus,
Heteromycteris, Solea, Soleichthys, Typhlachirus and
Zebrias), the STC is reduced on the blind side (Figure 21b);
in Microchirus, the STC is reduced on the blind side and
canaliculi are unbranched; in Buglossidium, Monochirus
and Vanstraelenia, the STC is reduced on both sides (Figure
21c); in Aseraggodes, Leptachirus and Liachirus, the eyed
side SOC in the nasal and the STC on both sides are absent,
the OTC and the POC are absent on both sides or they occur
as dermal canals that are not associated with the skull bones
and pass over the pterotic and preoperculum, respectively
(Figure 21d,e).
3.2.15
|
Family Cynoglossidae
The most extreme reduction of the main lateral line canals
is found in this family. Symphurus species (in the mono-
typic subfamily Symphurinae) lack all canals of the head. In
both genera Cynoglossus and Paraplagusia of the subfam-
ily Cynoglossinae, only the short portions of the PRC in the
preoperculum on both sides and the COC in the frontal bones
are present (Figure 2a,b). The other main canals (SOC, IOC,
FIGURE 18 Achiropsettidae.
Reduced pattern of the lateral line canals of
the head of Achiropsetta tricholepis (a) and
Pseudomancopsetta andriashevi (b). Arrow
shows absence of otic canal
FIGURE 19 Samaridae. Reduced
pattern of the lateral line canals of the head
of Samariscus sunieri (a), Samaris costae
(b) and Samaretta perexilis (c)

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15
VORONINA et Al.
OTC, POC nd MDC) associated with the skull bones are
absent. Instead, dermal canals passing on both sides of the
head within the scales are present. Their course differs con-
siderably from that of the canals typical for other flatfishes.
Canaliculi are branched.
4
|
DISCUSSION
4.1
|
General description of LLS of
flatfishes
An analysis of original data collected in combination with
a literature survey from a total of 304 species in 121 genera
belonging to 14 families shows both a common plan and di-
versity in the morphology of the LLS in Pleuronectiformes.
The main feature of the LLS of flatfishes is bilateral
asymmetry, which appears not only in the asymmetrical
course of the canals, especially in the orbital region, but also
in different combinations of the reductions of the canals or
the portions of canals which occur independently on the eyed
and blind sides of the head. Canal reductions are found in
the majority of the 121 flatfish genera examined (Table 2).
The reduction in the eyed side IOC is most common being
found in 92% of genera studied. The portion of the IOC in
the infraorbitals and in the lacrimal is each absent in half of
the 92% of the genera. The IOC is totally absent in the other
half of the genera. The blind side SOC is reduced in 40% of
genera, the blind side IOC is reduced in 43%, the blind side
MDC in 41%, eyed side MDC in 36% and both sides STC in
about 20% of genera. Rare reductions of the eyed side SOC
and OTC, and the POC and PRC of both sides occur only in
3%–7% of genera studied. Branched canaliculi are found in
half of the genera studied, and they are unbranched in the
other half of genera.
The combination of canal reductions (i.e. the absence of
the canals or their portions and unbranched canaliculi) varies
considerably and characterize taxa at the generic and in some
cases of suprageneric level. The complete pattern of the LLS
in which all canals are present and interconnected and have
highly branched canaliculi is found in 30 genera, whereas the
other 91 genera have a reduced pattern with more than two
canal reductions.
4.2
|
Taxonomic distribution of the
LLS patterns
Nine of 14 flatfish families can be defined by characteristics
of the LLS. A complete pattern is found in the monotypic fam-
ilies Psettodidae and Paralichthodidae and in Tephrinectes
sinensis. Unique LLS characters, such as the passage of
the blind side IOC through the fused infraorbital and fron-
tal bones and the passage of the OTC through the sphenotic
bone, separate the Psettodidae from the rest of the pleuronec-
tiforms. This distinction agrees with other morphological
(Cooper & Chapleau, 1998; Hoshino, 2001, 2006) and mo-
lecular studies (Berendzen & Dimmick, 2002; Betancur‐R,
Li, Munroe, Ballesteros, & Ortí, 2013; Campbell, López,
Satoh, Chen, & Miya, 2014; Mirande, 2017; Shi et al., 2018).
A reduced pattern is the only pattern found in seven fami-
lies (Table 7). Each of these seven families can be character-
ized by different combination of reductions. Three reductions
are common for all achirids, and four other reductions are
usual for the bothids. Five reductions are typical for all sole-
ids, and another five are typical for all achiropsettids. Nine
reductions are common in both the samarids and poecilop-
settids. The maximum number of canal reductions is found in
the Cynoglossidae, where either all main canals are absent or
only COC and short portions of the PRC are present.
Both complete and reduced patterns are found among
genera within five other families. Within the Citharidae,
FIGURE 20 Achiridae. Reduced pattern of the lateral line.
Canals of the head of Achirus scutum (a), Achirus achirus (b),
Apionichthys dumerili (c) and Gymnachirus nudus (d). Arrow shows
long canaliculus of coronal commissure, solid lines—dermal portions
of the canals

16
|
VORONINA et Al.
a reduced pattern in Brachypleura and Lepidoblepharon
distinguishes them from the other two genera that have
a complete pattern. This is consistent with the separa-
tion of Lepidoblepharon from Citharus and Citharoides
as suggested in molecular data analyses (Betancur‐R &
Ortí, 2014; Campbell et al., 2014; Pardo et al., 2005)
and contrasts the close relationship among all citharids
based on osteological study (Hoshino, 2001). Among
scophthalmids, a reduced LLS pattern in Zeugopterus
and Phrynorhombus supports the separation of these
genera in a phylogenetic analysis that was based on
osteological data (Chanet, 2003) and might be evi-
dence for division of this family into two subfamilies.
In Paralichthyidae, a reduced LLS pattern distinguishes
the genus Thysanopsetta from the other genera in the
family. Two reductions in the LLS in Cyclospetta,
Citharichthys, Etropus and Syacium distinguish these
genera within the paralichthyids and warrant the split-
ting of the Paralichthyidae that has been repeatedly sug-
gested (Betancur‐R et al., 2013; Harrington et al., 2016;
Munroe, 2015). In the Pleuronectidae, only a complete
pattern is found in the subfamilies Atheresthinae and
Pleuronichthyinae which have a basal position on a re-
cent phylogenetic tree (Vinnikov et al., 2018). In the
pleuronectid subfamily Hippoglossinae, a complete pat-
tern is found in all genera except for Lyopsetta which has
a reduced pattern. A reduced pattern is found in pleu-
ronectid subfamilies Microstominae and Pleuronectinae
except in Acanthopsetta, which has a complete pattern.
In the Rhombosoleidae, a complete LLS pattern in
Oncopterus distinguishes it from all other genera in the
family, which have a reduced pattern.
TABLE 3 Presence of a reduction (+) in the infraorbital (IOC), supraorbital (SOC) and supratemporal (STC) canals of the ocular (o) and
blind (b) sides of the head and presence of unbranched canaliculi (+) in citharids
Genera
Canal and their portions
Unbranched
canaliculi
SOC (o) SOC (b) IOC (o)
IOC (b) STCNasal bone Nasal bone
Interorbital
part of frontal
bone
Lacrimal
bone
Infraorbital
bones
Lepidoblepharon   +  +  + +
Brachypleura + +  + + +  
FIGURE 21 Soleidae. Reduced
pattern of the lateral line canals of the
head of Austroglossus microlepis (a),
Solea elongata (b), Buglossidium luteum
(c), Aseraggodes dubius (d) and Liachirus
melanospilos (e). Solid lines show dermal
canals or their portions

|
17
VORONINA et Al.
4.3
|
Evolution of LLS patterns
When mapped onto the most recent flatfish phylogeny, the
distribution of complete and reduced LLS patterns high-
lights the dynamic and complex nature of LLS evolution in
this order (Figure 22). The evolutionary significance of the
transformations of the LLS remains poorly understood, espe-
cially in view of the still unknown LLS patterns in the sister
group of the Pleuronectiformes. The ancestral state char-
acter reconstruction shows that a reduced pattern evolved
independently several times. The last common ancestor of
clade 1 has a reduced pattern with reversal to a complete
pattern in Oncopterus. The last common ancestor of clade
2 has a complete pattern, but a reduced pattern evolved
in Zeugopterus and Phrynorhombus (Scophthalmidae),
Thysanopsetta (Paralichthyidae) and in the Bothidae. The
ancestral character state for clade 3 is equivocal with differ-
ent patterns found in the subfamilies of this clade—complete
pattern in Hippoglossinae (except in Lyopsetta) and a re-
duced pattern in Microstominae and Pleuronectinae (except
in Acanthopsetta).
Both complete and reduced LLS patterns are found in flat-
fishes with the same feeding habits but, on the other hand, one
pattern is found among taxa with different feeding strategies
TABLE 4 Presence of a reduction (+) in the infraorbital (IOC), mandibular (MDC), preopercular (PRC) and supratemporal (STC) canals of
ocular side (o) of the head, presence of unbranched canaliculi (+) and interruption between canals (+)in scophthalmids
Genera
Canal and their portions
Unbranched canaliculi MDC‐PRC interruption
IOC (o)
MDC (o) STCLacrimal bone Infraorbital bones
Lophopsetta  +    
Lepidorhombus + +    
Zeugopterus + +  + + +
Phrynorhombus + + + + + +
TABLE 5 Presence of a reduction (+) in coronal commissure (COC), infraorbital (IOC), mandibular (MDC), preopercular (PRC) and
supraorbital (SOC) canals of the ocular (o) and blind (b) sides of the head, presence of unbranched canaliculi (+) and interruption between canals
(+)in pleuronectids
Genera
Canal and their portions
Unbranched
canaliculi
MDC‐PRC
interruption
COC
interruption
SOC (b) IOC (o)
MDC
Nasal
bone
Interorbital
part of fron-
tal bone
Lacrimal
bone
Infraorbital
bones
Atheresthes, Hippoglossus,
Pleuronichthys, Verasper
  +     
Reinhardtius      +  
Acanthopsetta  +    +  
Clidoderma      + + 
Eopsetta  + +     
Cleisthenes + +    +  
Glyptocephalus, Isopsetta,
Lepidopsetta, Limanda,
Parophrys, Platichthys,
Pleuronectes, Psettichthys,
Tanakius
 + +   +  
Dexistes, Myzopsetta + + +   +  
Liopsetta  + + +  +  
Pseudopleuronectes + + +   +  +
Hippoglossoides + + + +  +  +
Microstomus + + + + + +  

18
|
VORONINA et Al.
TABLE 6 Presence of a reduction (+) in coronal commissure (COC), infraorbital (IOC), mandibular (MDC), preopercular (PRC), supraorbital (SOC) and supratemporal (STC) canals of the
ocular (o) and blind (b) sides of the head of the head, presence of unbranched canaliculi (+) and interruption between canals (+) in rhombosoleids
Genera
Canal and their portions
Unbranched canaliculi MDC‐PRC interruption
SOC (b)
IOC (o) infraorbital
bones MDC STC COCNasal bone
Interorbital part of
frontal bone
Pelotretis   +    + +
Psammodiscus + +    +  
Colistium + +     + 
Ammotretis  + +   + + 
Rhombosolea  + +   + + +
Azygopus  + + + +  + +
Peltorhamphus  + + + + + + +
TABLE 7 Presence of a reduction (+) in the infraorbital (IOC), mandibular (MDC), preopercular (PRC), supraorbital (SOC) and supratemporal (STC) canals of the ocular (o) and blind (b) sides
of the head, presence of unbranched canaliculi (+) and interruption between canals (+) in six families of pleuronectiforms. Only reductions common for all genera of the family are presented
Family
Canal and their portions
Unbranched canaliculi MDC‐PRC interruption
SOC (b) interorbital
part of frontal bone
IOC (o)
IOC (b) MDC (o) MDC (b) STCLacrimal bone Infraorbital bones
Achiridae  +  +  +   
Bothidae +  +    + + 
Achiropsettidae   + +   + + +
Soleidae  + + + + +   
Samaridae  + + + + + + + +
Poecilopsettidae  + + + + + + + +

|
19
VORONINA et Al.
(Figure 22). The majority of flatfishes have eurybathic ver-
tical distribution inhabiting a very wide range from 50 to
2,000 m, and they have the same or different LLS pattern,
which is independent of depth (Figure 22). This preliminary
analysis does not directly reveal any obvious relationship of
LLS patterns with either of these aspects of flatfish biology.
Future comparative analyses of the morphological changes
in the particular canals in relation to fish size, depth range
and feeding habit will help to reveal how LLS evolution has
occurred within and between particular taxa of flatfishes.
4.4
|
Taxonomic use of LLS characters
Diversity of the LLS is most informative for taxonomy
at the generic level given the uniformity of LLS charac-
ters among all species within a genus. Substantial dif-
ferences in the LLS have been demonstrated between
the scophthalmid genera Scophthalmus and Lophopsetta
(Voronina, 2009), among the paralichthyid genera
Hippoglossina, Paralichthys and Lioglossina (Voronina
& Diaz de Astarloa, 2012) and among the pleuronectid
genera Liopsetta, Pleuronectes and Pseudopleuronectes
(Voronina & Chanet, 2014). These differences have been
used as part of the morphological evidence to define the
samarid genus Samaretta (Voronina & Suzumoto, 2017)
and for dividing the pleuronectid genera Limanda and
Myzopsetta (Vinnikov et al., 2018). The differences in LLS
among species reveal heterogeneity within other genera.
For example, the presence of normal (narrow) canals on the
blind side in G. kitaharae distinguishes this species from
all other Glyptocephalus species that have widened canals
on the blind side, a character that is not found in other flat-
fishes, and is evidence against putting these species into
one genus. Reduced canals in M. bathybius distinguish this
species from other Microstomus species, and a reduced IOC
occurs only in some Trinectes species. The taxonomic value
of LLS characters at the suprageneric level is not so obvi-
ous and definitive. However, differences in LLS morphol-
ogy can be used to define taxonomic distinctions within the
Scophthalmidae and the Citharidae and for a reconsidera-
tion of the position of Oncopterus within Rhombosoleidae
or Thysanopsetta within the Paralichthyidae.
The current study has drawn our attention to two LLS
patterns that can be discerned among Pleuronectiformes
and shows the importance of the LLS as a source of taxo-
nomic characters. These findings should allow researchers
to test additional hypotheses concerning the evolution of the
Pleuronectiformes.
ACKNOWLEDGEMENTS
We thank A. Balushkin and O. Voskoboinikova (ZIN, St.
Petersburg) for discussions on lateral line canal morphol-
ogy and helpful comments on the manuscript; G. Volkova,
E. Pavlova (ZIN, St. Petersburg), P. Pruvost, R. Causse, Z.
Gabsi (MNHN, Paris), J. Williams, S. Raredon (USNM,
FIGURE 22 Ancestral state
reconstruction of complete (black) and
reduced (white) patterns of the lateral line
canals. Phylogeny of order simplified from
Betancur‐R and Ortí (2014), Pleuronectidae
phylogeny simplified from Vinnikov et
al. (2018). Categories of feeding strategy
and data on their taxonomic distribution
summarized from De Groot (1971). Data
on habitation depth summarized from
Evseenko (2000) and from Voronina and
Volkova (2003). Three genera with lateral
line canal pattern different from their close
relatives are shown with the dashed line
either because of the absence at phylogeny
tree (Thysanopsetta) or their position within
clade (Acanthopsetta, Lyopsetta). D, day‐
feeders using visual or visual and chemical
means; N, non‐visual night‐feeders

20
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VORONINA et Al.
Washington), M. McGrouther, A. Hay, S. Reader (AMS,
Sydney), A. Suzumoto (BPBM, Honolulu), J. Maclaine
(BMNH, London), E. Vasil'eva (ZMMU, Moscow) and B.
Sidlauskas (OS, Corvallis) for providing kind assistance
and access to the specimens examined, and these Institutions
for their continued curation of valuable research mate-
rial and for help with Institutional loan of specimens. The
study was partly supported by a State Assignment AAAA‐
A17‐117030310197‐7. We also thank anonymous reviewers
for thorough, constructive and helpful suggestions that con-
siderably improved the manuscript.
ORCID
Elena P. Voronina https://orcid.
org/0000-0001-6602-3932
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How to cite this article: Voronina EP, Sideleva VG,
Hughes DR. Lateral line system of flatfishes
(Pleuronectiformes): Diversity and taxonomic
distribution of its characters. Acta Zool. 2019;00:1–25.
https ://doi.org/10.1111/azo.12311
APPENDIX 1
SPECIMENS EXAMINED FOR LATERAL
LINE SYSTEM COMPARISON
Tephrinectes sinensis 2 specimens (specs) 120 and 178
mm standard length (for all specimens) MNHN 1959‐0577
25°0'N, 125°0'E, ZIN 55719 Vietnam, Nha Trang.
Psettodidae: Psettodes belcheri 2 specs 181 and 225 mm
MNHN 1967‐0922 Benin; P. bennettii 6 specs 310–395 mm
MNHN 1941‐0066 Mauritanie, MNHN 1965‐0541 Senegal.
Citharidae: Brachypleura novaezeelandiae 6 specs 50–90
mm ZIN 21740 Myanmar, Tanintharyi coast; ZIN 46713
20°55′N, 88°01′E, ZIN 55106 and 55290 Gulf of Tonkin,
MNHN 1890‐354, 1890‐0355, 1890‐0336 India, Ganjam;
Citharoides macrolepidotus 1 spec 125 mm ZIN 45093
Japan, Obama; C. macrolepis 4 specs 170–225 mm ZIN
49720 22°19′S, 43°06′E; Citharus linguatula 2 specs 113
and 163 mm ZIN 4605 Mediterranean Sea, Palermo, ZIN
41004 Western Africa, Cap Blanc; Lepidoblepharon oph-
thalmolepis 2 specs 130 and 236 mm ZIN 55086 8°36'S,
157°28'E, MNHN 2014‐1066 New Caledonia.
Paralichthyidae: Ancylopsetta dilecta 1 spec 150 mm
MNHN 1896‐0152 northern part of Atlantic Ocean; A.
quadrocellata 1 spec 163 mm OS 2741 Florida, near Gulf
Breeze; Cephalopsetta ventrocellatus 4 specs 120–165
mm ZIN 48915 9°05′N, 75°59′E; Citharichthys arctifrons
2 specs 120 and 190 mm ZIN 23827 Atlantic Ocean; C.
dinoceros 2 specs 100 and 105 mm ZIK 4657, Atlantic
Ocean, Old Bahama Bay; C. gilberti 1 spec 86 and 108
mm ZMMU 13583 Pacific Ocean, Peru, OS 1587 Mouth of
Anton River, Gulf of Panama; C. macrops 2 specs 170 and
155 mm ZMMU 14824, 22°23′N, 88°10′E, ZMMU 12741,
28°10′N, 90°83′E; C. sordidus 1 spec 194 mm ZIN 23817
Pacific Ocean, Puget Sound; C. spilopterus 3 specs 110–155
mm MNHN 0000‐2945 French Guiana, Cayenne, MNHN
1876‐0739 Brazil, Rio de Janeiro B569; C. stampfi 2 specs
120 and 122 mm MNHN 1967‐0927 Congo Pointe‐Noire;
C. stigmaeus 3 specs 61–85 mm ZIN 23811 Pacific Ocean,
Puget Sound, ZIN 3984 San Francisco; C. xanthostigma 1
spec 130 mm ZIN 38516 29°10′N, 115°14′E; Cyclopsetta
fimbriata 1 spec 235 mm ZIN 54268, North West Atlantic
Ocean; Etropus crossotus 5 specs 75–117 mm ZIN 21733
Mexico, Mazatlán, MNHN 1942‐1A13, OS 1988 Gulf of
Panama off Rio Anton; E. longimanus 2 specs 105 and 124
mm ZIN 54426 Argentina, Mar del Plata; Gastropsetta
frontalis 3 specs 90–185 mm MNHN 1937‐0290 24°37'N,
82°58'W, ZMMU 14825 22°23′N, 88°107′W; Paralichthys
adspersus 6 specs 225–315 mm ZIN 55143 41°19′S,
73°58′W, ZIN 55146 42°19′S, 74°20′W; P. microps 2
specs 87 and 102 mm BMNH 1880.7.28.6 (holotype) West
Coast of Patagonia, Chile, ZIN 8733 Chincha Islands; P.
lethostigma 1 spec 96 mm MNHN 1999‐0458 New York;
P. triocellatus 3 specs 145–194 mm ZIN 52204 37°49′S,
56°35′W; Pseudorhombus arsius 1 spec 145 mm ZIN
36010 South China Sea, Hainan; P. cinnamoneus 3 specs
215–247 mm ZIN 51737 29°00′N, 124°30′E, ZIN 55322
western part of Yellow Sea; P. diplospilos 1 spec 185 mm
MNHN 1987‐0110 Vietnam, 8°12' N; 107°46' E; P. du-
pliocellatus 2 specs 150 and 185 mm ZIN 48910 7°36′N,
77°49′E; P. elevatus 1 spec 54 and 66 mm ZIN 55530 and
55531 Vietnam, Nha Trang; P. javanicus 2 specs 112 and
141 mm ZIN 55528 and 55529 Vietnam, Nha Trang; P.
oculocirris 2 specs 134 and 142 mm ZIN 55532 and 55533
Vietnam, Nha Trang; P. oligodon 4 specs 71–86 mm ZIN
55523‐55526 Vietnam, Nha Trang; Syacium guineen-
sis 2 specs 185 and 225 mm ZIN 49499 Western Africa,
Conakry; S. micrurum 2 specs 110–157 mm ZIN 3275
Brazil, Bahia; S. ovale 2 specs 106 and 108 mm OS 1584
Pelado Island, Gulf of Panama, OS 1585 Mouth of Anton
River, Gulf of Panama; S. papillosum 1 spec 180 mm ZIN
3276 Brazil, Bahia; Tarphops oligolepis 5 specs 51–62
mm ZIN 23102 Nagasaki, ZIN 22769 and 36459 South
China Sea, Hainan; Thysanopsetta naresi 1 spec 115 mm
ZIN 52182 off Chile; Xystreurys rasile 3 specs 115–310
mm ZIN 51743 37°49′S, 56°35′W, ZIN 54427 Northern
Patagonia.
Bothidae: Arnoglossus aspilos 10 specs 50–80 mm
BMNH 1978.4.4.1 (syntype) East Indies, ZIN 55307 55058,
Vietnam, Nha Trang; A. dalgleishi 2 specs 125 and 127 mm
ZIN 48956 11°42′S, 62°01′E; A. debilis 3 spec 137‐151
BPBM 23666 Hawaiian Islands, Pailolo Channel; A. impe-
rialis 1 spec 85 mm ZIN 41005 Western Africa, Conakry;
A. kessleri 4 specs 45–60 mm ZIN 29615 and 55056, 55057,
Black Sea; A. macrolophus 4 specs 67–80 mm MNHN
2014‐2149 Madagascar, ZIN 56001 Vietnam, Nha Trang;
A. nigrifrons 1 spec 119 mm MNHN 1995‐1168 (holotype)
Chesterfield Island; A. sayaensis 7 specs 96–122 mm ZIN
49505 and 49746 Saya de Malha Bank; A. scapha 1 spec 265
mm ZIN 23743 New Zealand, Lyttelton; A. septemventralis
1 spec 85 mm MNHN 1995‐1170 (paratype) New Caledonia;
A. thori 4 specs 77–113 mm ZIN 21732 Plymouth, MNHN
1961‐0875 43°34'N, 7°25'E; Asterorhombus filifer 1 spec
98 mm BPBM 34871 (holotype) Northwestern Hawaiian
Islands, Midway Atoll; A. intermedius 3 specs 87–124 mm

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VORONINA et Al.
ZIN 49504 Gulf of Aden, ZIN 55643 Vietnam, Nha Trang;
Bothus guibei 4 specs 170–215 mm MNHN 1964‐0438 (hol-
otype), 1964‐0439 (paratypes) Annobón Island; B. myrias-
ter 4 specs 124–153 mm ZIN 48266 14°01′N, 73°50′E, ZIN
55710 Vietnam, Nha Trang; B. ocellatus 2 specs 87–96 mm
ZIN 55540 Caribbean Sea, Margarita Island; B. pantheri-
nus 2 specs 88 and 210 mm MNHN 0000‐8094 Hawaiian
Islands, ZIN 55718 Vietnam, Nha Trang; B. podas 4 specs
73–161 mm ZIN 4603, 55696, Mediterranean Sea; B. thomp-
soni 6 specs 65–104 mm BPBM 3398 (holotype), 23938,
Hawaiian Islands; Chascanopsetta howensis 1 spec 98 mm
BPBM 14892 (holotype) Lord Howe Island; C. lugubris 4
specs 275–235 mm ZIN 49747 12°14′N, 53°06′E; C. megag-
natha 5 specs 122–157 mm ZIN 48686 (holotype) 24°56′S,
88°32′W, ZIN 48687 (paratypes) 25°33′S, 89°11′W; C.
prognathus 2 specs 165 and 207 mm MNHN 2014‐0857,
2014‐0940 French Polynesia; C. prorigera 4 specs 200–315
mm ZIN 45356 Pacific Ocean, southern part of the Emperor
Seamounts, BPBM 24958 Northwestern Hawaiian Islands,
Hancock Seamount, MNHN 2014‐0874 French Polynesia,
Raiatea, 16°46'S, 151°22'W; Crossorhombus azureus 4 specs
49–106 mm ZIN 55663 Vietnam, Nha Trang; C. kobensis 1
spec 102 mm ZIN 22765 Misaki; C. valderostratus 3 specs
56‐69 mm ZIN 51736 11°42′N, 51°23′E; Engyprosopon
arenicola 4 specs 32‐56 mm BPBM 37239, 32754 Hawaiian
Islands Oahu; E. bellonaensis 1 spec 54 mm MNHN
1993‐0143 (paratype) Сhesterfield Island; E. grandisquama
3 specs 63‐95 mm ZIN 55897 Gulf of Tonkin; E. hawaiiensis
5 specs 29‐56 mm BPBM 25464, 31979, 34902, 37240 and
37863 Hawaiian Islands; E. hensleyi 7 specs 99‐125 mm ZIN
49126, 491230 and 49131 Saya de Malha Bank; E. hureaui 1
spec 36 mm BPBM 37783 Gulf of Aqaba, Eilat; E. latifrons 8
specs 74‐92 mm ZIN 49715 10°30′S, 61°10′E, BPBM 35476
Seychelles, ZIN 55539 Saya de Malha Bank; E. marquisensis
6 specs 27‐45 mm BPBM 37167 Marquesas Islands, Fatuhiva;
E. mogkii 5 specs 53‐75 mm ZIN 7522 Indonesia, Ambon,
BPBM 32305 Indonesia, Ambon, BPBM 22201 Philippines,
BPBM 29808 Indonesia, Lombok; E. raoulensis 3 specs
68‐78 mm ZIN 54008 25°14′S, 158°38′E; E. regani 2 specs
19 and 30 mm BPBM 32760 (holotype) and 32761 (paratype)
Easter Island; E. xenandrus 5 specs 58‐55 mm BPBM 23897
Hawaiian Islands, Oahu; Engyophrys sanctilaurentii 1 spec
115 mm ZIN 45022 25°06′N, 108°57′W; Grammatobothus
polyophthalmus 3 specs 50‐59 mm ZIN 55707 Vietnam, Nha
Trang; Japonolaeops dentatus 3 specs 140‐160 mm ZIN
48929 and 48931 Saya de Malha Bank, MNHN 1984‐0608
Philippines; Kamoharaia megastoma 2 specs 165 and 200
mm ZIN 55084 Philippines 14°0'N 120°10'E, ZIN 55720
Vietnam, Nha Trang; L. guentheri 5 specs 70‐108 mm
ZIN 48934 Western Hindustan, 21°59′N, 68°19′E, BPBM
20496 India, Madras; L. lanceolata 1 spec 73 mm BMNH
1931.11.16.2 (holotype) Dzushi, Japan; L. natalensis 1 spec
113 mm BMNH 1922.3.27.19 (holotype) South Africa, Natal;
L. nigrescens 5 specs 115‐158 mm BMNH 1927.1.6.56‐57
(syntypes) Western Indian Ocean; Gulf of Aden, ZIN 49490
16°01′N, 52°21′E; L. nigromaculatus 6 specs 70‐170 mm
BMNH 1922.3.27.14 (syntypes), BMNH 1922.3.27.13,
MNHN 2014‐2547, 2014‐1660, Western Indian Ocean,
Natal, ZIN 49717 25°05′S, 35°15′E; L. parviceps 1 spec
120 mm BMNH 1879.5.14.98 Arafura Sea; L. pectoralis 1
spec 159 mm BMNH 1922.3.27.20 (holotype) South Africa,
Natal; Lophonectes gallus 1 spec 124 mm ZIN 21718 New
South Wales, Port Jackson; Monolene antillarum 3 specs
99‐103 mm ZIN 55116 35°17′S, 52°29′W; M. helenensis 1
spec 160 mm ZIN 54230 Gulf of Guinea; M. microstoma 3
specs 113‐160 mm MNHN 1938‐0111 (syntype) Mauritania,
ZIN 41006 Western Africa, Cap Blanc, ZIN 54060 Atlantic
Ocean, Saint Helena and Ascension Islands; Neolaeops mi-
crophthalmus 4 specs 112‐138 mm BMNH 1922.3.27.12
(syntype) Western Indian Ocean, Natal, MNHN 2008‐1286
Vanuatu, MNHN 2014‐1832 Madagascar; Parabothus ama-
okai 1 spec 110 mm ZIN 46157 (holotype) 25°38′S, 85°26′W;
P. chlorospilus 5 specs 143‐164 mm BPBM 25039 Hawaiian
Islands, Pailolo Channel; P. coarctatus 8 specs 85‐200 mm
BPBM 24367 Hawaiian Islands, Pailolo Channel, MNHN
2015‐0191 New Caledonia; P. filipes 4 specs 61‐79 mm
MNHN 1994‐0361 and 1994‐0358 (paratypes) Chesterfield
Island; Perissias taeniopterus 2 specs 74 and 83 mm USNM
362514 Ecuador, Gulf of Guayaquil; Psettina iijimae 4 specs
47‐82 mm ZIN 48959 11°57′N, 74°50′E, ZIN 55697 Gulf
of Tonkin, 20°00′N, 108°31′E; P. multisquamea 1 spec 95
mm ZIN 45661 (holotype) 11°27′S, 61°35′E; Tosarhombus
longimanus 5 specs 69‐139 mm MNHN 1994‐0330–0333
and 1994‐0335–0342 (paratypes); T. smithi 1 spec 170 mm
ZIN 48971 11°48′S, 61°55′E; Taeniopsetta ocellata 6 specs
105‐136 mm ZIN 48946 and 55543 Saya de Malha Bank; T.
radula 9 specs 91‐111 mm BPBM 9850 Hawaiian Islands,
Pailolo Channel; Trichopsetta carribaea 1 spec 80 mm
MNHN 1966‐0737 (paratype) 11°6'N, 74°30'W; T. ventralis
1 spec 125 mm MNHN 1996‐0149 38°4'S 77°51'E.
Paralichthodidae Paralichthodes algoensis 3 specs
125‐213 mm USNM 261357, BMNH 1906.11.19.113,
1919.9.12.48 South Africa, Durban.
Rhombosoleidae Ammotretis elongatus 1 spec 185 mm
AMS I.42644‐00 Australia, Western Australia, Perth area,
32°S, 115°E; Colistium guentheri 1 spec 197 mm OS 1319
near Cape Saunders, New Zealand; Psammodiscus ocellatus
4 specs 54‐70 mm BMNH 2013.2.11.1‐4 (syntypes).
Achiropsettidae Achiropsetta tricholepis 8 specs 142‐350
mm ZIN 48193 52°45′S, 57°25′W, ZIN 48195 52°49′S,
57°21′W, ZIN 48664 46°05′S, 50°36′E, ZIN 48665 Campbell
Plateau, ZIN 48196 Indian Ocean, Ob’ Seamount, ZIN
55094 47°17′S, 59°54′W, ZIN 55095 46°39′S, 59°52′W;
Mancopsetta maculata 4 specs 52‐142 mm ZIN 54587
Patagonian shelf 47°17′S, 59°54′W; M. maculata antarctica
1 spec 207 mm ZMMU (holotype) 14183 53°38′S, 40°56′W;

24
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VORONINA et Al.
Neoachiropsetta milfordi 5 specs 320‐405 mm ZIN 54307
46°00′S, 49°20′E; ZIN 55108 47°17′S, 59°54′W, ZIN 55320
71°51′S, 173°57′E; Pseudomancopsetta andriashevi 85‐122
mm ZMMU 16262 (holotype) 45°49′S, 84°18′W, ZIN
48668 45°16′S, 157°29′W, ZIN 48669 South‐East Atlantic,
Discovery Seamounts.
Achiridae Achirus achirus 2 specs 95 and 135 mm ZIN
53430 Cuba, ZMMU 21115; A. mazatlanus 2 specs 47 and
87 mm USNM 397251 Off Golfo de Fonseca, El Salvador; A.
scutum 1 spec 103 mm ZIN 21721 Panama; Apionichthys de-
clivis 1 spec 75 mm ZIN 4397 Brazil; A. dumerili 2 specs 85
and 95 mm ZIN 4921 Suriname, ZIN 55119 French Guiana,
Kourou; A. natterei 2 specs 58 and 73 mm USNM 190294
Colombia, Leticia; Baiostoma brachialis 2 specs 27 and 37
mm USNM 26605 (syntype) Apalachicola Bay, Florida;
USNM 30463 (syntype) South Florida; Catathyridium
grandirivi 2 specs 116 and 130 mm MNHN 0000‐3318 (hol-
otype) 30°S, 30°W, ZIN 7061 Brazil, Rio Grande do Sul; C.
jeninsii 3 specs 77‐86 mm USNM 77397 Argentina, Buenos
Ayres; Gymnachirus melas 2 specs 116 and 122 mm USNM
291088 Florida; G. nudus 3 specs 100‐118 mm ZIN 54069
off Southern Brazil, MNHN 1975‐0305 23°25'S, 44°36'W;
Hypoclinemus mentalis 2 specs 95‐122 mm ZIN 55118
Brazil, mouth of Amazon River; Trinectes fimbriatus 2 specs
69 and 72 mm USNM 291011 Gulf of Panama; T. fluviatilus
10 specs 25‐40 mm USNM 81668 (syntypes) Rio Mamoni, El
Capitan, Panama, MNHN 1976‐0405 (paratype) Panama; T.
inscriptus 1 spec 75 mm ZIK 4651 Old Bahama Bay; T. mac-
ulatus 5 specs 80‐120 mm ZIN 23694 and 23697 Lynnhaven
Roads, New York, Boston; T. microphthalmus 1 spec 168
mm MNHN 0000‐3314 Brazil, Bahia; T. paulistanus 2 specs
59 and 84 mm MNHN 0000‐3317 Brazil, Rio de Janeiro,
MNHN 0000‐3099 Brazil; T. xanthurus 5 specs 50‐80 mm
USNM 397242 Off Golfo de Fonseca, El Salvador.
Soleidae Achiroides melanorhynchus 3 specs 50‐55 mm
ZIN 49127 Taiwan; Aezopia cornuta 3 specs 155‐181 mm
ZIN 55765 Vietnam, Phan Thiet, Mui Ne; Aseraggodes al-
bidus 1 spec 30 mm BPBM 38802 (holotype) Indonesia,
Sulawesi; A. borehami 2 specs 94 and 102 mm BPBM 33478
and 36867 (paratypes) Hawaiian Islands; A. chapleaui 1
spec 35 mm BPBM 15863 (holotype) Papua New Guinea,
Madang Province; A. corymbus 1 spec 63 mm BPBM 40512
(paratype) Northeastern Australia, Queensland; A. dubius 5
specs 60‐92 mm ZIN 55698 and 55699 Gulf of Tonkin; A.
firmisquamis 1 spec 31 mm BPBM 30652 (holotype) Palau
Islands, Oreor Island; A. heemstrai 1 spec 68 mm BPBM
40151 (paratype) South Africa, KwaZulu‐Natal; A. heraldi
1 spec 47 mm BPBM 18445 (holotype) Marshall Islands,
Kwajalein Atoll; A. holcomi 1 spec 58 mm BPBM 38448
(holotype) Hawaiian Islands, Oahu; A. kimurai 1 spec 52 mm
BPBM 22165 (holotype) Philippines; A. lateralis 1 spec 64
mm BPBM 10992 (holotype) Marquesas Islands, Uahuka;
A. lenisquamis 1 spec 82 mm BPBM 39610 (paratype) New
South Wales; A. longipinnis 1 spec 54 mm BPBM 36647
(holotype) Indonesia, Nil Desperandum; A. winterbot-
tomi 1 spec 46 mm BPBM 40444 (paratype) Philippines,
Siquijor Island; Austroglssus microlepis 2 specs 275 and
290 mm ZIN 42890 South‐Western Africa, Walvis Bay;
Bathysolea profundicola 1 spec 145 mm ZIN 41045 Western
Africa, Saint‐Louis; Brachirus orientalis 5 specs 68‐126
mm ZIN 55780 Vietnam, Nha Trang; Buglossidium luteum
5 specs 85‐110 ZIN 50349 North Sea, 54°13′N, 6°58′E;
Dagetichthys commersonnii 2 specs 99 and 102 mm ZIN
55043 Vietnam, 10°29′N 107°28′E; Dicologlossa hexoph-
thalma 2 specs 111 and 120 mm ZIN 41036 Western Africa,
Dakar; Heteromycteris hartzfeldii 1 spec 90 mm BPBM
37024 Papua New Guinea, Waga Waga; H. japonicus 3 specs
90‐120 mm ZIN 22908 Japan Sea, Tsuruga; Leptachirus al-
leni 2 specs 57 and 76 mm BPBM 40459 (paratypes) Irian
Jaya; L. kikori 3 specs 26 and 57 mm BPBM 40466 (para-
types) Papua New Guinea; L. robertsi 1 spec 52 mm BPBM
40506 (paratype) Papua New Guinea; Liachirus melanospi-
los 6 specs 79‐106 mm ZIN 55790 Vietnam, Nha Trang;
Microchirus variegatus 1 spec 115 mm ZIN 26389 Plymouth;
Monohirus hispidus 1 spec 110 mm ZIN 4256 Mediterranean
Sea; Parachirus diringeri 1 spec 102 mm MNHN 1996‐0118
(holotype) Réunion Island; Pardachirus marmoratus 1 spec
107 mm ZIN 10965 Madagascar, Loucoube; P. pavoninus
2 specs 143‐106 mm ZIN 55781 and 55783 Vietnam, Nha
Trang; Pegusa cadenati 2 specs 142 and 157 mm MNHN
1952‐0276 (paratype); P. lascaris 1 spec 95 mm ZIN 29630
Black Sea, Feodosia Gulf; P. nasuta 5 specs 99‐195 mm ZIN
20649, 21065, 32341 and 37378 Black Sea; Phyllichthys
sclerolepis 1 spec 137 mm USNM 174031 Australia, Gulf
of Carpentaria; Solea elongata 2 specs 93 and 98 mm ZIN
49117 Indian Ocean, 20°37′N, 70°17′E; Solea ovata 1 spec 5
mm ZIN 55910 Gulf of Tonkin, beach Bàng La; S. stanalandi
1 spec 104 mm BPBM 32806 (holotype) Saudi Arabia, Half
Moon Bay; Soleichthys dori 1 spec 95 mm BPBM 20784
(holotype) Gulf of Aqaba, Nuweiba; S. tubiferus 1 spec 139
mm ZIN 55773 Vietnam, Nha Trang; Synapturichthys kleinii
1 specs 165 mm ZIN 6832 Ligurian Sea, Nice; Typhlachirus
caecus 2 specs 77 and 80 mm MNHN 1942‐0080 Indonesia,
Bagan; Vanstraelenia chirophthalma 3 specs 135‐167 mm
ZIN 41034 Western Africa, Gambia, ZIN 55114 07°23′N,
12°47′W; Zebrias fasciatus 4 specs 178‐210 mm ZIN 31372
and 35591 Yellow Sea; Z. lucapensis 5 specs 94‐115 mm
ZIN 55774 Vietnam, Phan Thiet, Mui Ne; Z. quagga 2 specs
52 and 117 mm unregistered, Vietnam, Nha Trang; Z. synap-
turoides 2 specs 94 and 97 ZIN 46700 Western Hindustan,
20°52′N, 69°41′E.
Cynoglossidae Cynoglossus arel 3 specs 185‐233 mm
ZIN 55605 Vietnam; C. itinus 3 specs 90‐128 mm ZIN 55824
Vietnam, Nha Trang; C. kopsii 2 specs 58‐65 mm ZIN 55825
Vietnam, Nha Trang; C. puncticeps 3 specs 107‐115 mm ZIN
55847 Vietnam, Nha Trang; C. quadrilineatus 3 specs 13‐30

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VORONINA et Al.
mm unregistered Hainan Island, ZIN 55041 Vietnam, Hồ
Cốc; Paraplagusia bilineata 2 specs 115 and 198 mm ZIN
55850 and 55851 Vietnam; P. japonica 2 specs 197 and 216
mm ZIN 55601 Vietnam, 12°05´N, 109°12´E; Symphurus
microrhynchus 3 specs 48‐59 mm ZIN 55724 Vietnam,
12°18´N, 109°15´E.