HENSLEY AND AHLSTROM: PLEURONECTIFORMES 



673 



merals, epicentrals, hypomerals) as homologous with those of 

 lower teleosts (see Phillips, 1942). The presence of these bones 

 was the main reason both Chabanaud (1949a) and Amaoka 

 (1969) hypothesized that pleuronectiforms were polyphyletic 

 and that at least the Bothidae, and in the case of Chabanaud 

 also the Samarinae, were derived from some lower teleostean 

 group. Hensley (1977) presented arguments for interpreting the 

 pleuronectiforms as monophyletic and the presence of inter- 

 muscular bones in at least the Bothidae as being apomorphic. 



Chabanaud (1969) described intermuscular bones in Samaris 

 as being in two series. However, we recently e.\amined a cleared- 

 and-stained specimen and found differences with Chabanaud's 

 description. In the abdominal region, rib-like or intermuscular 

 bones are in three series. Bones of the middle series are un- 

 branched and in the horizontal skeletogenous septum. Most 

 bones of the dorsal and ventral series are branched. In the region 

 of the caudal vertebrae, there are only the dorsal and ventral 

 series. There are none of the dorsal and ventral myorhabdoi as 

 found in the Bothidae. Although the three series of bones found 

 in Samaris resemble the epimerals, epicentrals, and hypomerals 

 of bothids, a more detailed comparison is required before a 

 statement about homologies can be made. 



Amaoka (1969) interpreted bothids as lacking pleural and 

 epipleural ribs, but possessing the five series of intermuscular 

 bones. However, there is another interpretation. It is possible 

 that Amaoka's epicentrals (limited to the horizontal skeletog- 

 enous septum of the abdominal region) and abdominal hypom- 

 erals are homologous to epipleural and pleural ribs, respectively, 

 of other pleuronectiforms, and that the presence of myorhabdoi, 

 epimerals, and caudal hypomerals are apomorphic states. 



Postcleithra. — The absence of postcleithra was a character state, 

 apparently apomorphic, used by Norman ( 1 934) and subsequent 

 authors to distinguish the Soleoidei from the Psettodoidei and 

 Pleuronectoidei. However, an adequate survey of this character 

 has never been made among the pleuronectoids. In a preliminary 

 survey, we found postcleithra absent in certain pleuronectoids, 

 i.e., the Samarinae and the bothid genera Mancopsetta and Pel- 

 ecantchthys. Postcleithra are definitely present in the rhombo- 

 soleines Oncopterus, Azygopus. Ammotretis. and Colistium. but 

 they may be absent in Pelotretis. Pellorhamphus. and Rhom- 

 bosolea (Norman, 1934: fig. 25c; Chabanaud, 1949). Although 

 lack of postcleithra in pleuronectiforms is reductive, their ab- 

 sence in certain pleuronectoids may indicate a closer relation- 

 ship between some of these groups and soleoids than hypoth- 

 esized in the Regan-Norman model. The occurrence of this 

 specialization in Pelecanichthys is almost certainly an indepen- 

 dent reduction, since this genus shows several synapomorphies 

 with other bothids. 



Vomerine teeth. — Huhhs (1945, 1946) interpreted the presence 

 of vomerine teeth as a primitive state for the order, and we 

 concur. However, Hubbs presented this interpretation as evi- 

 dence that citharids and scophthalmids were closely related and 

 represented an intermediate grade in pleuronectoid evolution. 

 The presence of vomerine teeth cannot be used to infer phy- 

 logenetic relationships among pleuronectiforms. 



Fin spmes— Huhhs ( 1 945, 1 946) presented the distributions for 

 dorsal, anal, and ventral-fin spines in pleuronectiforms. Psei- 

 todes is the only genus with dorsal and anal spines. This genus 

 and the Citharidae are the only flatfishes with ventral-fin spines. 



Hubbs properly interpreted their presence in these groups as 

 plesiomorphic for the order. However, again, he used a hori- 

 zontal or eclectic approach and inferred a close relationship 

 between the citharid genera and interpreted the group as an 

 intermediate grade in pleuronectoid evolution. The presence of 

 these spines does not indicate phylogenetic (vertical) relation- 

 ships. 



Supramaxillae. — SxxpvdiVmxiWac occur in Psettodes and the cith- 

 arids Eucitharus and Citharoides (Hubbs, 1945). In Psettodes, 

 the bones are well developed and apparently present on both 

 sides. The two citharid genera have them reduced in size, con- 

 fined to the blind side, or sometimes missing. The presence of 

 these bones is plesiomorphic for the order and should not be 

 used to infer phylogenetic relationships. 



Ventral-fin placements and base lengths. — Evolution of ventral- 

 fin asymmetry in pleuronectiforms is not well understood. Most 

 of our knowledge concerning the relationship between ocular 

 and ventral-fin asymmetry has come from some rare examples 

 of reversals in forms with asymmetrical ventral-fin morphology 

 (see Norman, 1 934). For comparative purposes, i.e., attempting 

 to determine homologous states, it would appear to be more 

 correct to compare ocular and blind-side ventral fins between 

 groups rather than those of the right and left sides (see Hubbs 

 and Hubbs, 1945). At present, there are several problems in 

 using ventral-fin morphology to elucidate phylogenetic rela- 

 tionships. Most work here has dealt only with external mor- 

 phology and much of this has not been sufficiently detailed or 

 accurate. What is needed are thorough comparisons of basip- 

 terygia as well as fins. Due to the paucity of accurate and detailed 

 studies of these structures in flatfishes, it is not possible to ad- 

 equately define character states for an in-depth comparison 

 throughout the order. Thus, ventral-fin characters were not in- 

 cluded in Table 1 79. What follows is a discussion of general 

 patterns of ventral-fin morphology. 



Ventral fins with short bases and symmetrical placements 

 have been correctly considered plesiomorphic states in pleu- 

 ronectiforms, and any type of asymmetry in placement, size, 

 shape, o;^ meristics as having been derived from symmetrical 

 states (e.gir Norman, 1934; Hubbs, 1945; Amaoka, 1969). Most 

 ventral-fin characters used have involved positions of the fins 

 relative to the midventral line and relative lengths of the fin 

 bases. Unfortunately, symmetry (plesiomorphic states) in both 

 of these characters has been used to define groups. Short-based 

 fins and symmetry or near symmetry in placement and base 

 lengths occur in Psettodes. the Paralichthyidae (except the Cy- 

 clopsetta group), the Citharidae, most soleines, most or all Pleu- 

 ronectinae, and the Poecilopsettinae. States where the ocular 

 ventral fin is on the midventral line and has a base extending 

 farther anteriorly than that of the blind side form a continuum. 

 Thus, groups with the base of the ocular ventral fin only slightly 

 extended anterior to that of the blind side (origin of blind fin 

 at transverse level of about the second or third ray of the ocular 

 fin) are the Samarinae, possibly some Soleinae, Paralichthodes, 

 the Taeniopsettinae, and Monolenc, groups where the origin of 

 the ocular fin is farther anterior relative to that of the blind fin 

 are the Rhombosoleinae, all Bothinae (except Monolene). and 

 possibly some Soleinae. Two groups, the Scophthalmidae and 

 Achirinae, have both ventral-fin bases close to or virtually on 

 the midventral line and the anterior basipterygial processes ex- 

 tended. The Cyciopsetta group has the ocular fin on the mid- 



