Cooper and Chapleau: Monophyly and intrarelationships of the family Pleuronectidae 
71 I 
metry in the space between dentary and articular, 
as well as the dentary process, are reversals for 
Pleuronectinae. These reversals are also observed in 
some species of the Pleuronectini (Table 1). 
The fourth lineage in Microstomini represents the 
sister relationship between Microstomus and 
Glyptocephalus. Eight synapomorphies support this 
hypothesis (Fig. 15): intestine extending posteriorly 
into body cavity (87), unique for this lineage; more than 
20 caudal-fin rays, an increase from 18 or 19 (88); more 
than six branched caudal-fin rays (89); 36 to 41 caudal 
vertebrae, an increase from 25 to 35 (26); less than five 
infraorbital bones, a reduction from between five and 
seven (51); teeth incisorlike (70); single row of teeth on 
upper jaw (60); and hyomandibula without a broad 
anteroventral margin (18, Fig. 20. 
Exceptions to the distribution of these synapo- 
morphies do not indicate exclusion of any species 
defined in Glyptocephalus or Microstomus, nor does 
homoplasy suggest the inclusion of additional taxa. 
An increase in caudal-fin rays is only observed in 
one other pleuronectid, Pleuronectes platessus, which 
usually has 20 caudal-fin rays. An increase in the 
relative number of branched caudal-fin rays is also 
observed in Pleuronichthys decurrens , P. ritteri , and 
Pseudopleuronectes yokohamae . An increase in the 
number of caudal vertebrae is homoplastic in 
Reinhardtius (Hippoglossinae). A reduction in the 
number of infraorbital bones is not observed in 
Glyptocephalus kitaharai and Microstomus pacificus 
but is reduced in Pseudopleuronectes americanus. 
The incisorlike tooth structure is unique within 
Microstomini but is observed in Parophrys vetula, 
Pleuronectes, and Pseudopleuronectes . A single row 
of teeth on the upper jaw is also unique within 
Microstomini but is also observed in Psettichthys 
melanostictus (Psettichthyini) and Pleuronectini. The 
absence of a broadened hyomandibula is a reversal 
unique within this lineage of Glyptocephalus and 
Microstomus . All other taxa within the fourth lin- 
eage of Pleuronectidae have a hyomandibular with 
a broadened anterior margin (Fig. 2D). 
Genus Dexistes The monotypic genus contains 
D. rikuzenius (Fig. 15). The monotypic status of this 
species is based on the morphologlical characters 
examined for intrarelationships of Microstomini and 
the presence of an ocular-side postocular ridge (78). 
The latter character has an additional evolutionary 
step within the sister tribe Pleuronectini, uniting a 
clade comprising Limanda, Platichthys, Pleuronectes, 
and Pseudopleuronectes. 
Genus Pleuronichthys This genus contains seven 
species: Pleuronichthys coenosus (not examined), P. 
cornutus, P. decurrens, P. guttulatus, P. ritteri, P. 
ocellatus, and P. verticalis. This genus is identified 
by eight character transformations (Fig. 15): pres- 
ence of villiform teeth, autapomorphic for Pleuro- 
nichthys (79); large foramen in blind-side prefrontal 
(80); gill rakers on second hypobranchial reduced to 
one at proximal base (36); lateral process present on 
ocular-side frontal (81, Fig. 7B, IOC); 25 or less cau- 
dal vertebrae (82); ocular-side pterosphenoid reduced 
and not forming posterior margin of orbit (83, Fig. 
7B); blind-side pterosphenoid is similarily reduced 
(48, Fig. 7B); and ocular-side entopterygoid similar 
in size to that of blind side (69, Fig. 2, A and B). 
Pleuronichthys coenosus is assumed to be a member 
of this genus on the basis of presence of villiform 
teeth, reduced number of caudal vertebrae (24 to 25), 
and presence of a lateral process on ocular-side fron- 
tal (Sakamoto, 1984a). 
There are few exceptions to the distribution of char- 
acter states within Pleuronichthys, and instances of 
homoplasy do not indicate an alternative hypothesis. 
The large foramen in the blind-side prefrontal was 
observed in only one other species, Glyptocephalus 
stelleri. Reduction of gill rakers on the second hypo- 
branchial was not observed in Pleuronichthys 
ocellatus, which has at least two gill rakers on the 
second hypobranchial. The presence of a lateral pro- 
cess on the ocular-side frontal is also observed in 
Microstomus achne, M. kitt, and M. pacificus. How- 
ever, it is not nearly as distinct as that in Pleuro- 
nichthys. Only Platichthys flesus, P. stellatus, and 
Pleuronectes putnami (Pleuronectini) have also fewer 
than 25 caudal vertebrae. Reduction of the ocular- 
side pterosphenoid is not observed in Pleuronichthys 
ritteri, where the pterosphenoid separates frontal and 
parasphenoid to form the posterior margin of the 
orbit. Reduction of the blind-side pterosphenoid is 
also observed in Acanthopsetta and Hippoglossoides 
(Hippoglossoidinae). These two character states are 
reversals in the Pleuronectidae. The symmetry be- 
tween ocular-side and blind-side entopterygoids is a 
reversal of the asymmetrical structure observed prior 
to the Isopsettini. This reversal only occurs in 
Pleuronichthys and Glyptocephalus kitaharai . 
The intrarelationships of Pleuronichthys are not fully 
resolved. Pleuronichthys guttulatus is the sister spe- 
cies to all other species of Pleuronichthys (Fig. 15). Four 
synapomorphies unite P. cornutus, P. coenosus, P. 
decurrens, P. ocellatus, P. ritteri, and P. verticalis : dor- 
sal fin originates on blind side of head (84); reduced or 
absent cartilaginous interspace between blind-side pre- 
frontal and parasphenoid (85, Fig. 7B); mesethmoid 
forms only part of anterior margin of upper orbit (86); 
and ocular-side metapterygoid articulated with 
entopterygoid (54). This last feature is homoplastic 
because it is also observed in Reinhardtius hippo- 
glossoides and Limanda punctatissima. 
