HENSLEY AND AHLSTROM: PLEURONECTIFORMES 



681 



asymmetrical placement) are not as great as formerly thought. 

 Loss of a truly dimorphic optic chiasma would appear to be the 

 only synapomorphy proposed to date uniting the pleuronec- 

 toids. However, as previously discussed, a basically dimorphic 

 or monomorphic optic chiasma has been demonstrated in very 

 few pleuronectoid species. 



One might expect that we are well informed about the inter- 

 relationships among pleuronectoids. Unfortunately, all of the 

 past work has used the eclectic approach. Thus, scophthalmids 

 and citharids have been related horizontally as primitive pleu- 

 ronectoids, and bothids, paralichthyids, and pleuronectids as 

 higher groups. Again, an important character here is the optic 

 chiasma. Two states were recognized in pleuronectoids: (1) the 

 primitive one (for pleuronectoids) where the nerve of the mi- 

 grating eye is always dorsal regardless of eye position (i.e.. the 

 basically dimorphic state); and (2) the monomorphic state char- 

 acteristic of "'higher" pleuronectoids where the chiasma is fixed 

 regardless of reversals. It has been assumed that all bothids, 

 pleuronectids. and paralichthyids show the monomorphic state. 

 Some evidence from other characters indicates this assumption 

 is not valid. 



Due mainly to the work of Amaoka (1969) and one of us 

 (Ahlstrom), we have a good survey of the caudal-fin complex 

 of pleuronectoids. Patterns of hypurals 1^ are fairly well known. 

 The distributions of these patterns call into question much of 

 the current evolutionary model and classification of the Pleu- 

 ronectoidei. There are five patterns of hypurals in this group as 

 defined in the Regan-Norman model: Pattern 1 (Fig. 363 up- 

 per)— This is plesiomorphic for the order. Pattern 5 (Fig. 364 

 upper)— This pattern is limited to the Samarinae. We interpret 

 this pattern as a synapomorphy uniting the samarines. Pattern 

 2 (Fig. 361)— Within pleuronectoids this pattern seems to be 

 limited to Citharoides. It is apparently derived from pattern 1. 

 Pattern 6 (Figs. 360, 364 middle and lower)— This is an apo- 

 morphic pattern which is very distinctive. We consider it ho- 

 mologous in pleuronectoids where it occurs and a synapomor- 

 phy uniting these groups. Again, we are calling this group the 

 bothoids and it includes the Pleuronectinae. Paralichthyidae 

 (except Tephrinectes and Thysanopsetta). Scophthalmidae, 

 Bothidae (except Mancopsetta), and Brachypleura. Pattern 4 

 (Fig. 363 lower)- Within the pleuronectoids this pattern is lim- 

 ited to certain genera of Rhombosoleinae and Eucitharus. Based 

 on other characters, the homology of pattern 4 between these 

 groups is probably not true. 



Citharidae. — Many character states used to define this family 

 (Hubbs, 1945. 1946) are plesiomorphic for the order: (1) reten- 

 tion of pelvic spines; (2) retention of supramaxillae (Eucitharus 

 and Citharoides): (3) urinary papilla close to anus; (4) no union 

 of branchiostegals; (5) retention of vomerine teeth {Eucitharus, 

 Brachypleura. Lepidoblepharon); and (6) retention of short-based 

 ventral fins. Some are plesiomorphic for the Pleuronectoidei: 



( 1 ) basically dimorphic optic chiasma (at least in Citharoides); 



(2) gill membranes showing some degree of union, but still fairly 

 widely separated; and (3) loss of dorsal and anal-fin spines. The 

 only possible character state proposed to date that could be 

 interpreted as a synapomorphy for this family is the position of 

 the anus on the ocular side. Although we have not examined 

 many specimens for this character, it appears that deflection of 

 the anus to the ocular side is probably slight. Amaoka (1972b) 

 examined Brachypleura and attempted to redefine the Cithar- 

 idae. However, he still showed no synapomorphies for the group. 



EP(HY5''l 



HY5(4''I 



THC * HY2 -4(2+371 



HY5 * EP 



THC*HY3 + 4 



HYl +2 



Fig. 364. Caudal skeleton of Samanscus iriocellatus. Hypural pat- 

 tern 5 (upper), caudal skeleton of Cilhanchthys macrops. Hypural pat- 

 tern 6 (middle), and caudal skeleton of Hippoglossina oblonga. Hypural 

 pattern 6 (lower). SR = splinter ray. other abbreviations as in Fig. 359. 

 "V on distal end of fin ray indicates dorsal- and ventralmost branched 

 ray. 



