Cooper and Chapleau: Monophyly and intrarelationships of the family Pleuronectidae 
717 
whose jaws and dentition are nearly symmetrical, and 
species possessing more specialized dentition, jaw struc- 
ture, and diverse feeding habits at subsequent lineages. 
The monophyly and intrarelationships of basal lineages 
in the Pleuronectidae are not supported by a large num- 
ber of synapomorphies. This is inherent for taxa asso- 
ciated with basal lineages in which the majority of mor- 
phological features are plesiomorphic with respect to 
the ingroup under examination (Stiassny and de Pinna, 
1994). However, the position of these basal lineages is 
key in establishing the polarity of character states for 
the more advanced taxa in Pleuronectidae. 
Homoplasy observed in most of the 106 morpho- 
logical characters was expected in an analysis con- 
taining this many taxa. The alternative topologies 
within Pleuronectini (Fig. 18) were supported by 
homoplasy but do not have better character support 
than the intrarelationships determined through con- 
sensus. These alternative topologies are not any less 
parsimonious than the topologies summarized by the 
consensus tree. Instead, the limited occurrence of 
these alternatives indicates that these topologies are 
not as robust to homoplasy as those summarized in 
the consensus tree. The taxonomic nomenclature es- 
tablished by the consensus tree is not in contradiction 
with alternatives. Based on the cladogram, this classi- 
fication represents the most conservative nomenclature 
for such a diverse group of pleuronectids. 
The interrelationships within most genera cannot 
be confidently supported, either because of a lack of 
observed morphological variation (as in Glypto- 
cephalus, Hippoglossoides, and Pleuronichthys) or 
because of the large amount of homoplasy occurring 
at terminal nodes indicated by the low consistency 
index (ci=0.33) and a high retention index (ri=0.79), 
as in Limanda, Pleuronectes, Pseudopleuronectes , 
and Platichthys. In either instance, species interre- 
lationships for these taxa do not warrant a formal 
description based on synapomorphies from this study. 
Additional morphological characters, such as the 
number of dorsal- and anal-fin rays, homoplastic at 
higher levels of universality may prove informative 
for species-level relationships. The developmental 
information summarized in Ahlstrom et al. (1984) 
has been expanding owing to the commercial popu- 
larity of many pleuronectid species (for example 
Fukuhara, 1988; Markle et. al., 1992). Yet there are 
still many pleuronectid species for which informa- 
tion of this kind is not yet available. Despite this 
lack of information across the family, it is certain 
that these developmental data can also be used in 
the future to help resolve natural groups among well- 
documented pleuronectid species. 
The phylogenetic limitations of jaw and dental 
morphological characters is clearly illustrated in the 
convergent evolution of jaw structures observed be- 
tween the tribes Microstomini and Pleuronectini. 
This is most evident in the dentition of Glypto- 
cephalus, and Microstomus, compared with Plat- 
ichthys, Pleuronectes, and Pseudopleuronectes, both 
of which have single row of incisorlike teeth that 
sometimes form a continuous cutting edge. However, 
monophyly for these taxa, based on jaw morphology 
and dentition, is not supported by other character 
states observed in the cranial bones and branchial 
apparatus. These other characters clearly resolve the 
monophyletic status and intrarelationships of these 
two groups within each of the two tribes, Micro- 
stomini and Pleuronectini. The trend of character 
reversal, 19 in total (Figs. 6 and 15), observed in 
Microstomini suggests that some members of this taxon 
may be positioned at a more basal node in Pleuro- 
nectidae prior to the fourth lineage. However, this al- 
ternative is not supported in any of the 128 most parsi- 
monious trees. This analysis clearly places Micro- 
stomini as a lineage within the Pleuronectinae on the 
basis of 28 character states that were not reversals. 
Six pleuronectid species were not examined in this 
analysis. They are Clidoderma asperrimum , 
Hippoglossoides dubius, Microtomus shuntovi, 
Pseudopleuronectes obscurus , Pleuronichthys 
coenosus, and Reinhardtius evermanni. These spe- 
cies are classified as members of Pleuronectidae on 
the basis of morphological characters obtained from 
the literature. In addition, their phylogenetic posi- 
tion is based on examination of external characters, 
radiographs, and literature. The a posteriori classi- 
fication of these six species lends support for the func- 
tionality of this analysis, such that an individual 
species can be classified on the basis of uniquely de- 
rived features. 
Classification 
The objectives for a formal classification of the 
Pleuronectidae were to recognize large groups within 
the family and to ensure that only natural groups 
are represented in the classification. This implied a 
revision of the established nomenclature. However, 
changes were minimal and aimed mainly at simpli- 
fying the existing nomenclature with its many mo- 
notypic genera. 
Our results indicate that the Pleuronectidae is 
monophyletic and can be subdivided into 5 new sub- 
families: Hippoglossinae, Eopsettinae, Lyopsettinae, 
Hippoglossoidinae, and Pleuronectinae. This classi- 
fication is based on the 50% majority-rule consensus 
of 128 parsimony trees, obtained through heuristic 
search (Fig. 1). This is the first classification based 
on a complete phylogenetic analysis of the group. It 
