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Fishery Bulletin 96(4), 1 998 
Genus Microstomas This genus contains five 
species: M. achne, M. bathybius, M kitt ., M . pad ficus , 
and M. shuntovi (not examined) and is defined by 
three synapomorphies (Fig. 15): posterior extension 
of supraoccipital absent (46, Fig. 10B); first anal 
pterygiophore thin ( 15); teeth in both upper and lower 
jaws uniform in length forming a continuous cutting 
edge (16, Fig. 9D). Descriptions of Microstomus 
shuntovi indicate that this species is very similar to 
M. kitt (Borets, 1983). The teeth are described as 
“chisel-like” (Borets, 1983), a term that similarly 
describes teeth in other species of Microstomus. An 
examination of the supraoccipital and the first anal 
pterygiophore would verify this classification. 
Absence of the posterior extension on the supraoc- 
cipital has evolved independently in the Hippo- 
glossoidinae. The thin structure of the first anal 
pterygiophore is a reversal of a thickened structure 
defining the third lineage. The continuous cutting 
edge of the teeth is an advanced state, also present 
in Glyptocephalus zachirus, Pleuronectes glacialis, 
P . pinnifasciatus , P . putnami , and Pseudopleuronectes 
schrenki. 
Microstomus bathybius is the sister species to M. 
achne, M. kitt , and M. pacificus (Fig. 15). This deep- 
sea species is unique in being the only pleuronectid 
with a series of infraorbital bones on the ocular side 
(8). It is the only species of Microstomus in which 
the blind-side nasal bone is absent (50) and is the 
only pleuronectid in which the anteroventral tip of 
the pelvis is anterior to the cleithrum (90). The other 
species of Microstom us share four character states 
(Fig. 15): ocular-side scales with radii completely 
surrounding the focus (91); margins of intero- 
perculum and suboperculum fimbriated (92, 93, Fig. 
2C); and haemapophysis present on most posterior 
abdominal vertebrae (6, Fig. 4D). This last feature 
is a reversal for Pleuronectidae, and only Glypto- 
cephalus zachirus has also a fimbriated subopercular 
margin. 
Genus Glyptocephalus This genus contains four 
species: G. cynoglossus, G. kitaharai, G. stelleri, and 
G. zachirus. Four synapomorphies are hypothesized 
at this node (Fig. 15): more than 21 caudal-fin rays 
(88); cleithra inserted by tip of urohyal (94); pres- 
ence of two to four pyloric appendages and two or 
three on upper intestine, an increase from two to 
three and one on upper intestine (95); sphenotic pro- 
cess positioned low on sphenotic and forming dorsal 
roof of hyomandibular socket (37, Fig. 7A). This last 
character is a reversal of that observed in all other 
Microstomini and Pleuronectini. 
Glyptocephalus kitaharai is the sister species to 
G. cynoglossus, G. stelleri, and G. zachirus. It is 
unique within this clade and with all other pleuro- 
nectids in having 23 caudal-fin rays, the highest 
number observed in the family (88). The other spe- 
cies are united by three character states (Fig. 15): 
blind-side nasal bones larger than those of ocular side 
(96); development of large mucous cavities on blind- 
side head (97), both characters unique for these three 
species; and presence of an interpterosphenoid bar 
(98, Fig. 16), not observed in any other species of 
Glyptocephalus or immediate lineages, but homoplas- 
tic in Hippoglossoides, Acanthopsetta, Psettichthys, 
Limanda aspera, L. ferruginea, L. proboscidea, L. 
punctatissima, Pseudopleuronectes americanus, P. 
yokohamae, and Pleuronectes. The monophyletic sta- 
tus of these three species is in agreement with rela- 
tionships inferred through an analysis of body shape 
(Chiu, 1990). 
Tribe Pleuronectini The tribe Pleuronectini con- 
tains 20 species (19 examined). Four synapomorphies 
define this tribe (Fig. 6): at least two regular rows of 
teeth on fifth ceratobranchial (49, Fig. 3, C and D); 
postocular ridge present on ocular side (78); upper 
jaw teeth in single row (60); and dorsal crest extend- 
ing anteriorly from supraoccipital to blind-side fron- 
tal reduced or absent (52, Fig. 10, D and E). 
Exceptions and homoplasy did not indicate an al- 
ternative hypothesis for Pleuronectini; all 19 species 
examined were grouped in all 128 of the equally par- 
fro i j 
{ \ , frt> 
i \ ^ iP ts b ar 
pts /t vffl 
Ip 
#<Qn 
pro MB 
so " 
Figure T 6 
Ventral aspect of cranium, Pleuronectes quadri- 
tuberculatus USNM 064042, with parasphenoid 
removed to reveal interpteroshenoid bar. frb= 
frontal (blind side); fro, frontal (ocular side); ipts 
bar = interpterosphenoid bar; pro = prootic; pts = 
pteroshenoid; so = supraoccipital; sp = sphenotic. 
Anterior region of orbit and occipital region have 
been removed. Scale bar is 10 mm. 
